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Testing Electronic Components

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1. 146 Sk Tesino arce 150 S2 Tesino E a a EDDIE 152 35 Testine Rela E TERNES 159 34 Technical Books for 166 SAM GI m 167 safety First Whenever you re working on any electronic equipment your own safety has to come first Every electronic technician must always take safety precautions before he or she starts work Electricity must be handled properly or else it can injure or cause fatalities Here are some basic steps that show you how to avoid accidents from occurring 1 Electrical Shock Once you open up a set cover you re actually exposing yourself to the threat of electric shock Always keep in mind that safety has to come first A serious shock may stop your heart and if large electric current flows through your body you will receive serious burns Here are some rules which should help you to avoid electricity hazards a Always turn off the equipment and unplug it before you begin to work b Ifyou have to run tests while the equipment is operating turn the equipment on make your test carefully and then turn the equipment off again C Wear rubber bottom shoes or sneakers d Try to do the work with one hand while keeping the other in your pocket That keeps the possible current paths away from the heart e Don t attempt repair work when you are tired or rushed f Always assume that all the parts 1n the power supp
2. eios etia DU Li Pests Colb DHOUCtoE oi ied ooo b e aseo Sa Tro SE eob inve 55 I2 Testing SWwItc D6S S sess VE PR 60 T3 DIOGG cio eei t Eoo Eo PR M NEU 63 14 Testing Bridge Rectifier eeee ee eese 67 15 Testing Light Emitting Diode LED 71 16 Testing Zener Di de o ooece eese saa ee ran rae o 73 17 Testing Linear Transformer eere eene 76 18 Testing Switch Mode Power Transformer 83 19 Understanding Capacitors eee esee 89 20 How to Discharge Capacitor eee eene Content 21 Tesina Capacitor secsec 98 22 Testing Capacitors That Breakdown When Under Full Operating Volf A96 Rui PEU VON 103 23 Testing Ceramic Capacitor ecce eee enn 106 24 Testing Voltage Regulator IC eese 109 25 Testing Optoisolator 21 5 isse 113 26 Testine Transistor S PRO RR Pads 117 27 Testing Field Effect Transistor Mosfet 130 28 Testing Darlington Transistor e eee eee ee ene 134 29 Testing Horizontal Output Transistor 142 30 Testing Silicon Controlled Rectifier SCR
3. am Set your meter to X1 Ohm and e the black probe to center pin make sure you already off the Monitor and the red probe to Base and Emitter It should not have any reading If you get a reading it could be the HOT or the surrounding components Shave problems It is very easy to check on board if the HOT 15 shorted or not Using your analogue meter set to X 1 Ohm and place the back probe to centre 143 collector pin and the red probe to both side of the HOT one at a time the pointer should not kick means no reading If you get a reading when the read probe touches on either one of the pins at the right base or left emitter chances are high the HOT had shorted You need to remove the HOT from the board and retest again The above method only applies when checking HOT on board Checking HOT off board is completely different from the above Testing HOT off board DU ZJUO VA aerem ne ZDU JUOLJ ISU ZI BU 2515 AF Si N PC Monitor HA 1500 800V 9A 45W BU 2515 AX Si N BU 2515AF BU 2515 DF Si N Di oi E1C integr Damper Diode BU2515DX Si N Di p mam Damper Diode BU 2520 A SiN CTV HA hi res 1500 800V 10 125W BU 2520 AF BU 2520 150 45W BU 2520 AW BU 25204 BU 2520 AX BU 25204 Iso 45W BU 2520 D BU 2520 integr Damper Diode BU 2520 DF BU 2520D Iso 45W BU 2520 DW BU 2520D BU 2520 DX Si N Di BU 2520D Iso 45W s BU 2522 A SN t With damp
4. AC DC current range Black test lead plugs into meter terminal marked Common Com or 2 Red test lead plugs into meter terminal marked Or V Q mA Now that you know the very basic of a multimeter describe how you can use the meters analogue and digital to take voltage resistance and current readings in the next few chapters Precaution While Using Multimeter Don t give shock or vibration to the multimeter especially analogue meters which have a delicate meter movement Sometimes even a slight fall from the repair bench to the floor could cause the digital meter LCD panel to cracked Even if after the zero ohm adjuster turned to maximum the pointer still does not reach zero replace the batteries Batteries out of life must be immediately removed from the meter otherwise components inside will get corroded by leakage of the battery electrolyte When you are not certain of the voltage or current value measurement 1s always started on the highest range to know its approximate value Lower range may be selected accordingly Read and understand the manual book that comes with your multimeter Don t replace any meter fuse with one having a higher current rating or slower response time In other word do not replace the fast blow fuse with a slow blow fuse Go to fuse chapter to know more fuses Don t take any resistance Ohm measurement in a circuit that has any power applied otherwise it may cause the components insid
5. Setting buzzer range to test a fuse with digital meter 53 Testing fuse using the buzzer function The red and black test probes can be either way when test on fuses Testing fuse is one of the simplest tasks in electronic troubleshooting it is easy and fast For fuse replacement use only the same current and voltage ratings as the original one 54 Testing Coil Inductor Typical examples of cous or inductors Testing coil 15 very easy compares to checking three leads components such as SCR FET and etc In general a coil consists of many turns or wire wrapped around a common core The core could be made of iron or even air It is label as L on circuit board When an electric current passes through the coil a magnetic field is produced A coil in some respects acts just opposite a capacitor A capacitor blocks DC while allowing AC to flow through it a coil allows DC to flow through it while restricting AC current flow Another name for a coil is an inductor FT ri 52 n a 1 ps any 55 vinding at these pins 2 pu s p T This is a Monitor B coil and don t mistaken it to be a n E transformer Observe there s only ome point in and one rene Coil or inductor can be test using an analogue inductance or a coil meter such as the dick smith flyback tester A coil that 1s small in size I would usually just test it with analogue meter and you could check it o
6. 32 Colors Numbers NEM Black 0 Brown ENNN gt BEEN Orange 3 Yellow 4 P Green 5 sos Violet 7 Ges White 9 Gold 5 Silver 10 Resistor Colour Code Typical Example on How to Calculate The Resistor Color Codes Reading from left to right the first band close to the edge gives the first digit in the numerical value of R The next band marks the second digit The third band is the decimal multiplier which gives the number of zeros after the two digits Example 1 red violet gold The first band 15 red for 2 and the next band is violet for 7 The red multiplier in the third band means add two zeroes to 27 The result can be illustrated as follows red violet red 2 7 x 100 2700 Therefore this R value is 2700Q with tolerance 5 The resistor tolerance means the amount by which the actual R can be different from the colour coded value For instance the alone resistor value 2700Q resistor with 5 percent tolerance can have resistance 5 percent above or below the coded value 33 This therefore is between 25650 and 28350 The calculations are as follows 5 percent of 2700 1s 0 05 x 2700 135 For 5 percent the value 1s 2700 135 2 2835 For 5 percent the value 1s 2700 135 2565 Q Example 2 green blue orange silver green blue orange 5 6 x 1000 560000 Therefore the R value is 560000 or 56kQ with tolerance
7. 10 Silver is 10 please refer back to table 1 Example 3 orange 4i black The example 3 illustrates that black for the third band just means do not add zeroes to the first two digits Since this resistor has orange orange and black band the R value is 330 with tolerance 4 595 Example 4 brown grey black silver 18 x 17180 Therefore the R value is 18Q with tolerance 10 34 Example 5 brown green gold gold For these values the third band 1s gold indicating a fractional decimal multiplier When the third band is gold multiply the first two digits by 0 1 Refer back to table 1 The R value is brown green al gold 1 5 x 0 1 1 50 5 Example 6 yellow violet gold silver 47 x 0 1 4 7Q 10 Example 7 Ted red silver gold For these values the third band is silver When the third band 1s silver multiply the first two digits by 0 01 refer back to table 1 The R value is red silver gold 2 2 x 0 001 2 0 220 5 Example 8 blue grey silver silver 1 68 x 0 01 0 680 10 35 Example 9 Green brown black red brown The first band is green for 5 the next band 15 brown for 1 and the black for 0 The red multiplier in the fourth band means add two zeroes to 510 The result can be illustrated as follows 510 x 100 51000 Therefore this R value is 51000Q or 51kQ with tolerance 1 brown Example 10 yellow orange blue orange Is
8. At this time the meter doesn t show any reading Now gently move the black probe and touch the Gate pin the black probe still 148 touching the Anode pin and you will notice the meter s pointer will kick as shown at the picture low resistance TT pm _ m rs i I PY mh c 7 r i eo IL or Ps i x i Oe AU bo Move black probe to tmxh gate pin MT MN YR E T 7 3r Removing the black probe from he GATE pin the black probe still touching the Anode pin ou would noticed that the resistance continues to be there low resistance This 1s due to he conduction of SCR as the eter battery 1s usually able to supply current more than the holding current If at this stage you removed the black probe from the Anode a pin and connect it back the Em pointer will dropped back to STNG P infinity high resistance If the t SCR could hold the resistance hen the SCR is considered good If it can t hold then the SCR is faulty Conclusion Practice testing SCR more often to see how s the result like Try some different part numbers and power SCR and if the resistance don t hold using X1 ohm you may try X10 ohm and etc 149 Testing Triac Typical example of Triac Main Terminal 2 MTZ Main Termianl 1 MT1 The TRIAC symbol The triac is an electronic switch or relay with three terminals It comes in many shapes sizes and
9. B Collector C and Emitter E There are two configurations for a common transistor NPN and PNP as shown in Figure 1 Notice the difference symbols for NPN and PNP transistor The emitter arrow points away from the transistor body for an NPN and toward the transistor body for PNP C C E NPN PNP Fig 1 The circuit symbols for the two transistor types a NPN b PNP 117 EIEE LII L T4 ESTEE ar N 2 v 62 Tai Boa rt t 6969 a WE LSZE maze Ua FIZE PODA 1 soze Transistors in Computer Monitor board Transistor s Function The main operational characteristic of a transistor 1s that a small voltage placed on one of the three leads can control a large amount of current flow through the other two leads This enables a transistor to perform two basic functions 1 A transistor can act as an electronic switch turning current flow ON and OFF transistor amplify a signal making it larger in amplitude Since the transistor is capable of amplifying a signal it is said to be an active components Devices such as resistors capacitors inductors and diodes are not able to amplify and are therefore known as passive components Either type transistor NPN or PNP can perform essentially the same function in an electronic circuit The main difference between an NPN and a PNP transistor in a circuit is the direction in which electrons
10. flyback transformer B coil and horizontal deflection coil before using my digital or analogue meter to do testing PUWER hen measuring the B coil the Led lights went off and it suppose o show at least 5 LED bars and ester above Upon soldering out the coil I did not see any burn mark at the winding or loop and in fact it looks shiny Because I trust the meter I opened up the winding and to my surprised the internal winding had burnt into crisp but the outer winding looks good indeed A new B coil restored the monitor to life By using a flyback tester or coil tester for testing coil it has helped me to locate many shorted coils in switch mode power transformer primary winding B coil flyback transformer primary winding and horizontal deflection coil The flyback meter can even be used to check the condition of ballast in fluorescent lamp too 58 Even if there is short m the winding inductance meter could not test it Only by using coil meter such as the dick mith flyback meter the short circuit can be detected wy Using Flyback Tester To Test Flyback Transformer As for the flyback tester you can either buy or make one yourself Recently I found that the main supplier temporarily stopped production on this dick smith flyback tester However you can make one yourself by visiting this website http www flippers com pdfs k7205 pdf 59 Testing Switches o A com
11. no power erratic power and even power shut down once switch on the equipment Many technicians and engineers do not know that they can actually test the optocoupler with their analogue multimeter Most of them thought that there 1s no way of testing an IC with an analogue meter Since we already knew the optocoupler pin out from the schematic diagram testing this IC 1s just the same as measuring a normal bipolar transistor and LED In order to accurately check optoisolator ic you need to use an analogue multimeter Test the LED using the times 10k ohms range It should have one reading when checking both ways If you 114 have 2 readings then the LED have become shorted The testing method is exactly the same when you are checking a normal diode The LED mainly connected internally to pin 1 and 2 of the optocoupler IC To check the phototransistor set your meter to times 1 ohm range and place your black probe to the base of the transistor and the red probe to collector and emitter It should show 2 similar readings Then move your black probe to collector and red probe to base and emitter of the transistor It should not register any reading The last step 1s to place your black probe to emitter and the red probe to base and collector of the transistor Again it should not register any reading in the multimeter An Optoisolator in Electronic Board Now turn your meter selector to times 10k ohm range to measure the collector an
12. pointer moved then pin 1 is the 123 uming there is no reading when black probe placed in pin 1 and red probe to pin 2 and 3 now you move he black probe to pin 2 and red probe pin 3 and 1 If there is reading the centre pin would be Base The diagram in Figure 2 assumes you are testing an unknown type of transistor Set your meter to the lowest ohm s range 1 e Rx1Q From the six combination of test result you will know the transistor 1s belonging to which type Black probe Red probe Reading is connected 15 in ohms to pin no connected to pin no Low Low High High High High Figure 2 Identifying transistor type and pin leads 1 Connect the black probe of the multimeter to one of the transistor leads and connect the red probe to any of the other leads 124 2 If two low readings are found for one connection of the black probe test no 1 amp 2 while each of the other two position gives two high readings test no 3 4 5 amp 6 then the transistor is NPN type 3 The pin where the black probe is connected to showed two low reading when the red probes connected to the other two leads shows high reading is the Base In the above case pin 1 is the base Checking PNP transistor you have to start with the red probe Place the red probe to pin 1 and then black probe to pin 2 and 3 If the pointer moved then pin 1 is the BASE Your test probe plac
13. resistor The pointer points to about 15 ohm Use 15 ohm multiply by 1 K and you will get 15 K Ohm Check the result to see if the pointer point to near or exact 15 K Ohm If the resistor has 5 tolerance the pointer should point between the values of 14 25K to 15 75K Ohm Any value you get that 1s not between the tolerance ranges you should replace the resistor 41 Please make sure before measuring it you Measuring a 100 K Ohms resistor Pointer points ultiply by 10 K you will get SUE Ohms In order to check a 100 K ohm resistor you have to select the X 10 K Ohm range Follow the procedure explained above and you should be able to get the measurement Using Digital Meter to Test Resistor Select this Ohms range when est resistor with digital meter 42 Personally I do not use analogue meter to test resistor as the result shown on the meter panel only makes you have to guess what the resistor value is You may ask yourself 1s it 47 ohm or 47 5 ohm or even 47 7 ohm By using digital meter the LCD display in your meter will show you the exact value of the resistance under test It is more accurate than using analogue meter 5 50 easy to test resistor with digital meter You don t need to do calibration or every test and the readout is direct First select the Ohm range and place your test probes across the two points of the resistor as shown in the photo Digital meter does not need any calibration compare to
14. this electronic component regulates an output voltage Pin 1 is the input dc voltage pin 2 is the ground and pin 3 is the output As the circuitry adds more load to a power supply the output voltage tends to drop A regulator circuit voltage regulator keeps the output voltage steady in spite of changes in the load Put it simple any dc voltage from 7V to about 38 V enters the pin 1 of 7805 voltage regulator then expect a 5 V output at pin 3 Any voltage in 109 between 7V to 38V will cause the voltage regulator to produce a steady 5 V output Do not exceed the 38 V rating otherwise the voltage regulator may burn You may check from the internet or any semiconductor data book preferably ECG master replacement guide about the specification of any voltage regulator Some famous part number uses in electronic circuits are 7805 7812 7905 and 7912 Part numbers that start with 78XX have positive output while the 79 XX series have negative output 7805 output 5 Volts voltage regulator found in r3electronic circuit board For your information the input voltage must have at least two volts higher than the input voltage That s mean if you want to get a 12 V output from a 7812 voltage regulator the input voltage have to be at least 14 V and above Don t expect to use a 5 V dc input to produce 12 V output this way won t work 110 Take a look at the diagram below Diode to convert AC Input Filter capacitors to remov
15. 3 of the voltage regulator IC Power the equipment and see the result If you get 8 Volts then the IC is working fine If you get 0 volts or 3 to 5 Volts then you have to measure the input voltage Make sure it has more than 10 Volts input voltage If the input voltage 1s lesser than 10 Volts say 6 Volts then suspect a fault in the power supply line or a leaky voltage regulator A leaky voltage regulator can pull down the input voltage Sometimes bad components in the output line can also pull down the output voltage of regulator The best is to direct replace with a new voltage regulator and retest it A new voltage regulator IC 1s very cheap and I encourage you to keep some spare for yourself for future use in electronic troubleshooting You may also desolder remove the output pin pin 3 so that it will not touch the line but pin 1 and 2 is still connected Power ON the equipment and check the pin 3 voltage If there is a good input but the pin 3 output still low say 3 Volts most probably the voltage regulator has turned bad and need to be replaced Testing voltage regulator 15 not difficult and if you have no confident in testing the IC with power ON I suggest you get someone who have experienced in the voltage testing to help you out You may even e mail me for the support 112 Testing Opto Isolator A Motorola 4N35 Optocoupler A lot of electronic equipment nowadays is using optocoupler in the circuit
16. 5 E 3 e pmi XT ja SMD type Resistor ay type uu une cn __ A Wire Wound Resistor 3l Resistor Colour Code Calculation Fixed resistors are marked in several ways These are 1 Color coding Straight numerical value iii Certain numerical codes that can be easily translated Because carbon resistors are small physically they are color coded to mark their R value in ohms In memorizing the colors note that the darkest colors black and brown are for the lowest numbers zero and one through lighter colors to white for nine Technicians must know this code Table 1 and 2 shows the colour code and their meanings Colour Digit Multiplier Tolerance First Band First Digit Second Band Second digit Third Band Multiplier Fourth Band Tolerance T First Band First Digit Second Band Second digit Third Band Third digit Fourth Band Multiplier Fifth Band Tolerance Black Brown Red Orange Yellow Green Blue Violet Grey White Gold Silver No colour 1 10 100 1000 10000 100000 1000000 10000000 0 1 0 01 ABLE 1 Showing four colours band of resistor and their meanings Tolerance Code Black Brown Red Orange Yellow Green Blue Violet Grey White Gold Silver 1 2 0 5 0 25 0 1 0 05 5 10 TABLE 2 Showing five colours band of resistor and their meanings
17. B 1000 TIP 130 80V TIP 130 100V E S L 60V 70W B gt 1000 P 135 80V TIP4 is a HPH type darlington a diode transistor Same to TIP 127 it i is a PHP type darlington a diode transistor Because of the built in diode the result that you get 1s completely different from testing the Darlington transistor that have no diode built into it It is difficult to find the Base Collector and the Emitter pins due to the built in diode I guess you have to refer to semiconductor data books or even the internet to look for its pin outs Testing this type of transistor 1s easy please refers to the photos below 138 WE Set to X 10 K Ohm and place the red probe to pin 1 and black probe to pin 2 and it should have a low reading Low Ohm reading ma Hitler L IUe Now move the black probe to pin 3 while the red probe still on pin 1 You should get a low reading TN a a probe to pin 2 and the black s Next move the re probe at pin 3 You should not get any reading M 139 to pin 1 and he red probe still at pin 2 You should not qet any reading If you et reading mean the transistor is 49 100 QU eee a OO Mak Mais c r tpe tre 1 ANI ro FN af e How move the r black probe to pin 2 You should get a low reading 140 Last place the black probe to pin 1 and the red probe still in pin 3 You should get a low reading I
18. To test the small blue resin coated ceramic disc capacitor that have the capacitor marking of 104 50v besides using digital capacitance tester to check for the capacitance value I also use an analogue meter Set to times 10Kohm range that has 12 volt output from the probes to check this type of ceramic capacitor failure Many times it will reveal the bad intermittent capacitors You will be shocked to see the digital capacitance meter tested ok when checking the capacitor but show a shorted reading when check with an analogue meter In the market there is certain brand of analogue meter that have the range of 100kohm If you remove the cover you can t see the 9 volt battery in it what you see is only the 2 pieces of 1 5 volt batteries This type of meter can t accurately detect the ceramic capacitor leakage because the output voltage from the probes was only 3 volt Ceramic capacitor manufacturer produced many construction and types of capacitors and if the ceramic disc capacitor always failed even though you had replaced a new one then try another type which 1s the resin coated ceramic disk capacitor Replacing a higher voltage rating than the original one may also help to prolong the life of the ceramic capacitor 108 Testing Voltage Regulator IC 7812 Voltage Regulator 7905 Voltage 7808 Voltage regulator Regulator Typical part numbers of Voltage Regulator a e 1 A voltage regulator IC As the name suggest
19. a full scale reading red probe to cathode and black probe to anode which mean the pointer will point towards the 0 ohms scale if you now connect the probe the other way black probe to cathode and red probe to anode the pointer will point to around 2 4 ohms If both ways of testing caused the pointer to point to zero ohms then the zener diode is considered shorted When you measure a 5 1 volt zener diode as usual one way will point to zero ohms while the other way will show a higher resistance which is in the 20 to 60 ohms These are the 74 characteristic of a good working zener diode and don t think that the meter shows two reading means the zener diode 15 faulty If you get two reading when you measure a normal diode then the diode is shorted As I mentioned above testing zener diode is totally different from checking a normal diode When you connect your probe and measure a 13 volt zener diode and above voltage it should show only one reading using the times 10 K ohms range That s mean when you are touching the red probe to the cathode and black probe to the anode Reversing the probe should not show any reading If the result shows two readings then the zener diode is confirmed to be shorted or have developed a leakage Start measuring zener diode taken out from your component s rack or from scraped electronic board compare a good zener diode and a shorted one and see for yourself Write it down in your book what are the r
20. about 0 Ohm Set your meter to buzzer sound to perform continuity test This is the right way to perform ntinuity test with digital meter set to buzzer range You can also use a digital meter that have the buzzer sound to test the connection If you heard the buzzer sound while measuring the wire or connection this means that the connection or internal wire 1s good 29 Resistance and Resistors The word resistance means opposition to some action In electricity resistance means the opposition to the flow of current The resistance 1s measured in ohm Q Resistance 1s also expressed in kilo ohms milli ohms etc With 10000 1 kilo ohms 10000000 1 mega ohms The symbol of resistance 1s show as AWA Symbol of a resistor It is noted by a letter R The main two characteristic of resistor are its resistance R in ohms and its power rating in watts W Resistors are available in a very wide range of R values from a fraction of an ohm to many mega ohms The power rating may be as high as several hundred watts or as low as 1 8 watt Always use a replacement resistor with a power rating that is equal to or greater than the original The value of the resistance can be measure by a multimeter 30 Types of Resistor 1 il 111 1V V Vl Carbon Composition Resistors Carbon Film Resistors Metal Film Resistors Wire Wounds Fusible Resistor Variable Resistor J pir d
21. black probe to 3 Now place your finger _ touch on pin 1 and 2 and you should see some low resistance reading Remember to set your 3nalogue meter to X 10 K Ohms 132 If you notice that all the result that you measured kicked towards zero ohms and will not discharge then the FET 1s considered shorted and need replacement Testing the P channel FET field effect transistor 1s just the same way as when you check N channel FET What you do is to switch the probe polarity when checking the P channel Some analogue multimeter have the times 100k Ohm range this type of meter can t really test FET due to the absent of 9 Volt battery inside the multimeter This type of meter will not have enough power to trigger the mosfet Make sure you use a meter that have the times 10k ohm range selector Typical N channel mosfet part numbers are 2SK791 K1118 IRF634 IRF 740 and P channel FET transistor part number are J307 J516 IRF 9620 and etc You can also get a mosfet tester from the market and one of the famous brands 15 the SENCORE tf46 portable super cricket transistor and FET tester You can bid one from EBay Sencore T F46 FET Tester 133 Testing Darlington Transistor C516 or BC516 TIP427 TIP422 Typical part numbers of darlington transistors 4 darlington pair transistor schematic This is two transistors connected together of two emitter followers in cascade so that the amplified current from the first is ampli
22. colors It 1s an open circuit with no gate signal present but conduct in both directions when gate voltage 1s applied Triac are used extensively in power control circuits They are particularly suite for AC power control applications such as motor speed control light dimmers temperature control and inverters They are also employed for over voltage protection in DC power supplies 150 Testing Triac Main Terminal 2 MTZ Main Terrnianl 4 MT1 Set to X1 Ohm 1 First make sure you know the terminals of the triac If you do not know you can always refer to a semiconductor data book or browse through the internet Once you have located the terminals it is the time to use your analogue meter set to X 1 Ohm or X10 Ohm 2 Place the red probe to terminal 2 and the black probe to terminal 1 You should get a high resistance reading 3 Now use a screw driver tip to create a momentarily short between the gate and terminal 2 or you can just move the red probe touching the gate while the red probe is still on the terminal 2 This short will cause the triac to turn ON and you will see a low resistance reading at the meter panel and remain low even the gate connection is broken 4 Reverse the probes and retest again and you should expect the same result These reading are approximate and may vary with manufacturer or different specification from the triac from experienced any result that is significantly different would
23. enough to burn your hand fingers and your skin when you accidentally touch it and the worst case is while you re carrying the Monitor or TV you might just throw off the equipment when you got a shocked from the filter capacitor and the cathode ray tube monitor may break and cause the flying glasses to hit your body or eyes Just be cautious when handling the power supply area You can always use a meter to confirm whether there is still charge in the capacitor Place your meter s black probe to the capacitor negative pin you can see the negative marking at the sleeve of the capacitor and the red probe to other pin If there is high voltage registered in your meter then you have to discharge the capacitor otherwise you may proceed to repair the equipment Typical value for this type of filter capacitor 1s 220 to 330 microfarad with a 400 to 450 voltage rating The large filter capacitor in power supply section 94 There are three ways to discharge the large filter capacitor in a switch mode power supplies 1000V220Uf E iltare capacitor Y Tlooking from behind the P j PIN rr j p 1 a r 1 F Al t 1 r 3 e 6 j v Do not use a screw driver to discharge the filter capacitor ko E Z2 Please don t use this method to discharge filter capacitor Discharging the capacitor with a screw driver not recommended The reason for not
24. exceeded the fuse rating The thin wire of fuse may be made of aluminium tin coated copper or nickel The resulting open in the circuit stops current to flow In electronic equipment most fuses are cylindrical glass or ceramic type with a metal cap at each end The current rating and voltage also can be seen in one of the two metal end caps N 9 Fuse symbol There are two popular physical sizes 1 4 X 1 4 inch and 5X20mm The 1 4 X 74 inch size is used in many automobiles You ll find both sizes in many electronic equipment but the smaller 5 X 20mm has become more common Fuses are available with current ratings from 1 500 Ampere to hundreds of amperes Fuse is label as F in circuit board Before showing you on how to test or check a fuse first you need to understand the purpose of a fuse The function of fuses is to stop higher than normal current to flow to an electronic circuit it is designed to protect equipment and save electronic components from being damaged 50 and also stop overheating which could cause a fire Sometimes though there were lightning strike on an equipment you will be surprised that only fuse were damaged and not the power supply section or components Op ad There are two basic types of fuses which 15 the E Y fast acting and slow blow type The fast acting E A Slow Blow Fuse fuse will open very quickly when their particular current rating is exceeded This is very i importan
25. is ar type darlington transistor RS R D GEM 2340088 EL Since you already know that it was a PNP type Darlington transistor then you have to start testing it by using the red probe The procedure of finding the Base Collector and Emitter 1s exactly the same as when you test on the normal transistor Set your analogue multimeter to X1 Ohm and place the red probe to pin 1 of BC516 and the black probe to pin 2 and 3 If the pointer shows no movement shift the red probe to pin 2 middle pin and the black probe to pin and 3 If there is movement in 135 the meter s pointer when the black probe touches on pin 1 and 3 then pin 2 1s the Base If you move the red probe to pin 3 and the black probe to pin 1 and 2 a good Darlington transistor should not have any reading setto X 1 Ohm red probe to pin 2 saand black probe to pin 3 and there This shows that the B on irm first that the black probe on pin 1 the pointer also must have T ay reading See the next photo below 53 Pointer shows a a 5 Tm _ some Jini ad X 3850TR TES asm nau E 0 it is confirmed that the pin 2 is the Base because there was a reading when the black probe was on pin 1 of the transistor 136 Since you have confirmed that pin 2 1s the Base we now move to the other steps to find the Collector and the Emitter Set to X 10 K Ohms and place any of
26. number and get the SCR specification Usually the SCR manufacturers will provide the full datasheet for those who want it Once you know the pin outs of the G A and C legs you can begin to test the SCR If you have the Peak electronic atlas component analyzer tester what you need to do is to connect the three small clips to each pin of the esting SCRE with Peak Atlas SCR any part bh Analyser number will do The tester will begin to analyze the SCR and prompt you with the display such as Sensitive or low power thyristor before it tells you the exact pin outs of G A and C After the first test the tester will eventually show you 147 the answer at the LCD display Red 1s Gate Green is Cathode and Blue 1s Anode It is a simple process and you will know the answer in less than 10 seconds If there is a problem in the SCR the tester would not be able to show the results instead it shows a shorted reading iL abe li L Let a P m RT By WM ny Make sure set to X1 ohms to test SCR eh F Fg ru 2 First mm need to put red probe ta C B and black probe to Showing the right way to check SCR If you don t have this tester for checking SCR I m going to show you another easy way on how to test SCR fast You need an analogue meter set to X1 ohm Place the red probe to the Cathode and black probe to the Anode pin
27. point to a faulty triac If possible get some triac with different specification and measure it to take down their measurement for future comparison 151 Testing Crystal Oscillator E EI a EI LJ E Eig LER A Crystal and location marking It s simple on how to test a crystal with a tester or checker Crystal oscillators are used to generate precise stable radio frequencies and are found in a wide variety of electronic equipment such as Computers motherboard and monitor Television Telecommunications systems mobile phone and etc The function 1s to keep the frequency of the clock from drifting If the signal from this clock stops producing frequency or is weak or the pulses begin to vary or change the electronic equipments might show intermittent problems or might stop altogether ght 199 Acer nc ics gt a gua Li E P 4545 Crystals in Computer Motherboard 152 The microprocessor pins that hold the crystal oscillator are usually called OSC IN and OSC OUT and the frequency is marked on the crystal The location of the crystals was labelled as XTAL or X Some examples of crystal oscillator frequency are 4 mega hertz 8 MHz 16 MHz and so on Crystal Symbol l T experienced quite a number of Computer Monitor crystal breakdowns causing the On Screen Display OSD to disappear from the screen Some On Screen Display even m
28. pointer should move a little bit up No movement indicates an open coil You may set the Using an external power supply to test relay The next step is to connect a power supply across the relay Use a variable regulated power supply to adjust to the same voltage as what the relay can handle That s mean if the relay specification is 5V then you 162 adjust the power supply to 5 V Any voltage higher than 5 V will burn the relay coil Now connect either the positive and negative alligator clip to the relay coil When the relay coil have the 5 V run through it the coil will begin to energize and start pulling the internal armature You actually could hear a tic sound from the relay when it is energized n hecking a normally close NC pins It should show low reading set to X 1 Ohm 163 voltage regulated power supply apply nto relay the coil energized and cause the Normally close NC internal contact li to become open circuit thus no reading was obtained z gNo reading from the Ssameter ee Bos pe it hecking the normally open Rare NO pin and the common pin here should be no reading because the internal contacts yas opened 164 External power supply Low Ohms reading o the coil the coil energized and Scause the normally open NO and the common pins to have contact thus the meter show a low reading If you place your analogue meter probes s
29. sign of the big filter capacitor Note make sure you discharge it first by referring to the capacitor topic Trace from the positive pin and eventually you will reach one of the SMPT pin Now trace from the centre pin of the power FET Again this FET pin will lead you to one of the pin of SMPT as shown from the photo Remove the SMPT and test the two pins with the coil flyback tester 86 ulii Pam E peis S n Wr Eik Seri E bnina LOPT FBT Once you fou nd the primary inding you can test it on or off board Or you can solder it put to test it off board Placing the flyback tester probes to the primary winding of the switch mode power transformers a good measurement will usually between of 87 4 8 bars LED lights up If it indicates only one or two LED bars or the flyback tester LED goes off no light this proof that the primary winding have problem If the primary winding shorted you can send the SMPT to a rewinding shop for repair 88 Understanding Capacitors Capacitor also known as condenser 15 one of the most essential components in designing an electronic circuit Radio television and monitor circuits use a number of capacitors Capacitor has a tendency to store electrical charge and then release it as current in the circuit where it is connected So the use of capacitor is to store and then release electrical charge This concept may sound simple enough but it has important applications when th
30. some field effect transistors are examples of ESD devices These components can be easily damaged by static electricity There are several techniques which can reduce the incidence of component damage caused by static electricity a Immediately before handling any ESD devices drain the electrostatic charge from your body by touching a known earth ground b Store ESD devices in conductive foam pad until installation in circuit c Wear a grounding strap attached to your wrist d Use only a grounded tip soldering iron to solder or desolder ESD devices Some suggest using a battery powered soldering iron when working on ESD circuits 10 Fire Before returning the equipment to the user every reasonable precaution 15 taken to avoid fire hazards Be sure to use only direct replacements and not one that defeats some safety measure For example the fuses in your equipment are carefully designed Fuses must be replaced only with the same size type and ratings Should you install a fuse that 1s too large than the original rating chances are that the equipment will be flammable ll Lifting Some equipment like TV Hi fi or Monitor can easily weight around 15 to 30 kilogram Many problems arise when lifting this equipment from the floor Wrong posture when lifting equipment may cause acute back pain The right way to lift is keep your back straight and upright and use your legs to supply the lifting power 12 Ventilation Be sure th
31. suggest that you get few of the Darlington transistor from electronic suppliers with and without built in diode to play around with it Record down all the steps you have taken to successfully test this type of transistors before you test on the bad or faulty Darlington transistor If you have the budget you can always get a transistor tester that can automatically test all kind of transistors but I can t guarantee whether it will give an accurate reading especially checking the Darlington transistor that have the built in diode More practice only makes you perfect in testing electronic components 141 Testing Horizontal Output Transistor nfl Hornzontaloutput i ransistor LT D j E T a f a 1 a 1 z E i 4 i a X WAAT d E amm ih Ls il M 4 ls nn LAE C mi E Horizontal Output Transistor HOT If you are repairing Television and Computer Monitor I m sure you had seen a horizontal output transistor HOT before This transistor is use to switch the flyback transformer and prone to become defective due to the stress of dealing with high voltage A shorted HOT will usually caused no power low power power cycling and power to shutdown The HOT 15 mainly a NPN transistor 142 Horizontal output transistor HOT in Monitor Testing HOT on board
32. supply while the cold ground is the equipment ground Be careful when taking voltage measurements around these grounds For example if you want to check the primary circuit of a power supply with power on always ground your meter or scope to the hot ground while check the secondary side using the cold ground If the Hot ground is not used and you use only the cold ground the voltage measurement might not be correct and it may destroy your meter One way to prevent this 1s to use an isolation transformer 4 Isolation Transformer his is a customized isolation ransformer that i use for repairing electronic equipment When servicing any electronic equipment always use an isolation transformer to protect yourself from an electrical shock During servicing the isolation transformer is connected between the equipment and ac power line An isolation transformer is a transformer that has a 1 1 turn ratio to provide the standard line voltage at the secondary outlet This means that it does not change the voltage The transformer still produces 240V AC at its outputs but both sides of this AC lines are independent of ground If you were to accidentally touch one of these outputs you would be protected The isolation transformer must be rated to handle the power of any equipment connected to it Typical ratings are 250 to 500W Note A variable transformer or variacs is not an isolation transformer 5 Discharging the Cathode Ray
33. using the screw driver to discharge a capacitor is because the printed circuit board or circuitry can be damaged due to the spark generated while discharging the high voltage in the capacitor I once have blown the power area using this method However if you knew that the capacitor stored voltage is not too large after confirmed it with a meter you can easily discharge it with a small screw driver Just place the screw driver tip to touch the two pin of the capacitor within seconds the charge will be gone If the capacitor holds a heavier charge of electricity then discharging the capacitor with a screw driver may melt the tip of the screw driver and the copper on the printed circuit board Sometimes a big spark may cause small disintegrated solder lead or copper to fly out from the circuit board and might injured your eyes or body 95 hese two wires connects 100 Watt light bulb A 100 watt bulb use to discharge filter capacitor Another method is that you can use a 100 watt electric light bulb and touch the two wires coming out from the light bulb on the leads of the capacitor This method had been used by many electronic repairers around the world for the light bulb will act as an indicator to see if the capacitor still holds the charge If there 1s a charge the light bulb will light and after discharged the light bulb will goes off I still preferred the third method because you have to use both hands to touch on the capacitor le
34. which 1s the capacitor dielectric or leakage test Use this test only when you want to check capacitors that have working voltage exceeding 250 volt By using an analogue insulation meter you will be able to test the capacitor leakage 104 ELLE n a s INBUEATION TESTER An Insulation Tester When I connect the filter capacitor to the meter and press the ready button it showed a very low resistance and this proved that a short circuit occurred between the plates when high voltage applied A good filter capacitor will just showed a charge and discharge in the insulation tester just like when you are testing a capacitor using analogue meter This proved that the bad capacitor breakdown when under full operating voltage You can get an insulation tester from any electronic suppliers It comes in few ranges of 100v 250v 500v 1000v and even 5000 volt If you want testing capacitor of 220 microfarad 400 volt then you have to select 250 volt If you select 500 volt it will blow your capacitor that is under test because the voltage you have selected 1s higher than 400 volt If possible you should get exact value and voltage for capacitor replacement Capacitor breakdown when under full voltage is quite rare and only happen to those capacitor that have 250 volts and above If you come across some tough dog repair and could not locate the fault in the electronic board I m sure you will know what meter to use now Go find the culpr
35. 33x10 3300000 picofarad or 3300 nanofarad 3 3 microfarad Electrolytic capacitors have their capacitance voltage rating and polarity printed on the case as shown in Figure below gt NOTE Arrow Points to Negative gt en m 22UF 16v 92 k N A 100 microfarad 16 volt electrolytic capacitor Capacitance Tolerance Ceramic disk capacitors for general applications usually have a tolerance of 20 percent Paper capacitors usually have a tolerance of 10 percent For closer tolerances mica capacitors are used It has tolerance value of 2 to 20 percent The letter after the capacitance numerical code indicates the tolerance 1 e M 20 K 10 J 5 So a 103K capacitor is a 10 000pF or 10nF or 0 010uF 10 capacitor with 10 tolerance Electrolytic capacitors have wide tolerance For instant a 100uF electrolytic with tolerance of 10 percent 20 percent may have a capacitance of 90 to 120uF 93 How To Discharge Capacitor Capacitor discharge is the first thing you should do as an electronic repairer before touching the power supply section The large filter capacitor in the power supply section can hold dangerous high voltage even if the unit has been off for few days It 15 advisable to discharge the filter capacitor first before you start to troubleshoot in order protect yourself from electrocuted Though the capacitor current stored in the capacitor can t kill you but it 1s
36. An optocoupler or sometimes refer to as optoisolator allows two circuits to exchange signals yet remain electrically isolated This is usually accomplished by using light to relay the signal The standard optocoupler circuits design uses a LED shining on a phototransistor usually it 15 a NPN transistor and not PNP The signal 1s applied to the LED which then shines on the transistor in the IC The light 15 proportional to the signal so the signal is thus transferred to the phototransistor Optocouplers may also comes in few module such as the SCR photodiodes TRIAC of other semiconductor switch as an output and incandescent lamps neon bulbs or other light source I also came across two led and two phototransistors in a package in the power supply of a NEC printer In this book I will explain only the most commonly used optocoupler which is the combination of LED and phototransistor See the optocoupler IC schematic diagram below 113 Anode Cathode Base An Optocoupler Symbol or Schematic The optocoupler usually found in switch mode power supply circuit in many electronic equipment It is connected in between the primary and secondary section of power supplies The optocoupler application or function in the circuit 1s to Monitor high voltage Output voltage sampling for regulation System control micro for power on off Ground isolation If the optocoupler IC breakdown it will cause the equipment to have low power blink
37. Rating of Capacitors Capacitors also have a voltage rating usually stated as WV for working voltage or WVDC This rating specifies the maximum voltage that can be applied across the capacitors without puncturing the dielectric Voltage ratings for general purpose paper mica and ceramic capacitors are typically 200 to 500 VDC Ceramic capacitors with ratings of 1 to 5kv are also available Electrolytic capacitors are commonly used 1 25 50 100 150 and 450v ratings In addition 6 and 10V electrolytic capacitors are often used in transistor circuits 90 CAUTIONS Never use a capacitor into circuit with higher voltages than the capacitor is rated for otherwise it becomes hot and may explode It s all right to replace a 0 22uF of 200WV capacitor with one rated 0 22uF 250WVDC Capacitor Safety A capacitor can store a charge for some time after equipment is power off High voltage electrolytic caps and even large value low voltage electrolytic can pose a safety hazard Usually these caps are in power supplies and almost have a resistor in parallel with the cap s called a bleeder resistor to discharge the cap after power is switched off If a bleeder resistor 1s open or there is none then the cap can retain a voltage charge after the unit 1s unplugged A large 75V capacitor in a high power audio amplifier can easily melt the tip of a screwdriver accompanied by flying metal sparks 1f the tool shorts across the capacit
38. Tube CRT Anode The CRT of a Monitor and TV can hold a dangerous charge even if the Monitor and TV have not been used several days All CRT have graphite coating on the internal and external surfaces of the glass bell This conductive graphite coating are commonly known as aquadag coating and it forms the two plates of a high voltage filter capacitor using the glass 1n between as dielectric The external coating is always connected to the Monitor and TV chassis ground by a spring arrangement around the CRT This high voltage filter capacitor has very low leakage Before removing a CRT ensure that you discharge this capacitor in order to prevent shocks Or serious injuries High Voltage Monitors and TV have sections that use very high DC voltages The high voltage 1s needed to be applied to the CRT to attract the electron beam to the phosphor This high voltage could be as low as 12 000 volt in a monochrome Monitor or as high as 30 000 volt in large colour monitor Flyback Transformer 15 the part that is used to generate the high voltage The high voltage circuit inside a Monitor or TV can give you a dangerous electric shock and causes you to jerk violently You could cut yourself by accidentally knocking on sharp chassis edges Be familiar with the high voltage circuits before you work on any high voltage equipment T X Radiation An X ray 1s a form of radiation produced when a beam of electrons strikes some material at a relativel
39. ad ou can use a 100 watt light bulb to discharge the filter capacitor The right way to discharge capacitor with light bulb 96 Use a resistor to discharge the capacitor leads Third method and also my favourite method are to place the leads of a high wattage resistor on the leads of the capacitors you want to discharge You can use either a 1 8 k or a 2 2 kilo ohm 5 to 10 watt resistor to discharge the high voltage capacitor in a switch mode power supplies It is very simple to use and very effective It takes only a couple of seconds to fully discharge the capacitor Please do not hold the two ends of the resistor with your finger only hold the body of the resistor Otherwise your fingers may get discharge from the capacitor Using only one hand you can do the job while the other hand you still can hold a solder gun or secure the equipment casing I strongly recommend to those who are using the screw driver to discharge a capacitor in power supply to consider the second and third method as these is the safest methods It not only protects the circuit it also protects you If you had discharge the capacitor and you are still not sure or no confidence whether the charge already gone you can always use a meter to confirm it 97 Testing Capacitor An Analog Multimeter First method before you test capacitor make sure you use an analogue multimeter set to time 1 ohm range and connect a capacitor to the test probe See
40. ample is 240v ac input with a 12 volt ac output low voltage 3 Isolation transformer produce the same amount of voltage as the input voltage Typical example 15 240 v ac input with a 240 volt ac output 77 a sure set to Check for any short circuit betaeen the primary and secondary winding It should not show any reading under x10 E ohm A single transformer can have different independent outputs to serve as a step up transformers as well as step down transformer The output voltages are then converted into DC voltages with the help of diodes I would not go too details into transformer theory as this page touch on the topic of how to test a linear transformer There are three ways or techniques on how to test a transformer p d 4 fa 2 set to range ki FI z 1 gt a ts zi XT ww a Ti x d E B p Transformer just like other component where it have tolerances T lus 9v ac output transformer produced 9 55 vac Please do not expect it to output 1 2 volt vac 78 Switch ON the equipment and measure the input and output voltage of the transformer with either an analogue or digital meter If there are no voltage or lower voltage then it suppose to be the transformer need replacement I personally liked this method because you are testing the transformer under full operating voltage which is very accurate The di
41. analogue meter where you have to adjust the adjuster to make it zero Ohm before you begin to do measurement The result shown at the LCD display of the digital meter is the exact resistance value of the resistor Digital meter really removed all the guess work Not only that many digital meter 1s auto range that s mean what ever value of resistor you want to check it will automatically prompt you the result without having you to adjust to a suitable range in order to test the resistor This saves time and accurate too 43 one num of resistor rom the circi board in order to do an accurate test If you are a beginner I strongly recommend that you remove all the resistors leg I mean only one leg and test it with your digital meter Hope with this secrets checking resistor should not be a problem to you anymore 44 Testing Variable Resistor Variable resistors also called potentiometers or rheostats employ a movable metal blade resting along a ring of resistive film You can change the resistance by turning the knob terminals Internal view of Variable resistor 45 The internal view of a Variable go Resistor Failure among variable resistors usually takes form of intermittent connections between the wiper blade and resistive film Sometimes it also can be burnt due to overload of currents and develop an open circuit Remember that film slowly wears away as the wiper moves back and forth across it Af
42. at your work place has good ventilation Prolong exposure or excessive inhalation of vapours from chemical spray and fumes from lead may cause damage to your nervous system or body 13 Laser Warning Labels If you are troubleshooting DVD VCD laser printer and other laser related products you will notice a laser warning label on or near the laser head assembly Do not stare at the laser beam at any time Always avoid directly exposing your eyes to the beam Prolong exposure of laser beam to the eyes may cause eye injury or loss of sight Do not attempt to adjust the laser gain controls by any methods other than those described in the service manual Incorrect adjustment can increase the laser radiation beyond acceptable limits You have to use a laser power meter to confirm the existence of a laser beam 12 Understanding Analogue and Digital Multimeter A Digital Multimeter Multimeters analogue and digital are one way in which you can see what s going on in an electrical circuit Voltmeters ohmmeters and ammeter are essential in all electric work Multimeters can go by many 13 names Some people call them as multimeter or just meter while others refer them as VOMs or multitesters or even tester They among the simplest and least expensive pieces of test equipment available that every electronic enthusiast should have A multimeter 15 as basic to an electronic technician as a brush 15
43. ay when you switch on the equipment To save the fuse you can use the series light bulb trick which I m going to share to you in other article Some fuses even die of old age because fuses have lifespan too But if the inside of the glass fuse is black colour or darkened and there is no trace of the fuse element the centre connector you know that there was a major short circuit somewhere in the circuit and most probably 1s the power supply unit Continuity test Measuring a fuse on board with an analogue multimeter The common type and current rating of a fuse in a Monitor and Power Supply is slow blow 3 15 to 5 Ampere 250 Volts Here is the part on how to test a fuse Switch off the power of the equipment remove the casing and you will see a fuse usually located in the Ac input area or power supply section Measure the fuse with a either an analogue or a digital multimeter If you use an analogue meter then select the lowest ohms range which is the x1 ohms 52 Touch the probes to both end of the fuse You can check the fuse while it still in circuit A good fuse reading should showed continuity or read ZERO ohms A blown fuse is open which will not show any reading on your meter You may also set to the buzzer range to test a fuse with digital meter If the fuse is ok the buzzer will sound and if the fuse 1s broken internally there will be no sound Set to buzzer to test fuse If the fuse is good you will hear a sound
44. d emitter of the transistor It should have no reading on one way and the other way should have a slight reading Which mean the meter s pointer will moved a little bit up from the infinity scale of the analogue meter If you get two readings then the optocoupler is faulty One of the most famous part numbers of optoisolator is the 4N35 If you want to know more about the internal diagram of any optocoupler IC I recommend that you check from the Philip ECG semiconductor master replacement guide book for the correct datasheet From the schematic it 1s easier to describe whether it 1s a phototransistor photodiode SCR or Triac type at the output of the optocoupler IC Once 115 you know which type of components inside the IC then you can use the necessary testing method to apply to the IC MASTER RETI G I DOG i HOPI regonaredd in optocoupler used m zr computer power supply crout a Optoisolator in Power Supply 116 Testing Transistor Typical transistors found in electronic circuits Transistors are solid state devices similar in some way to the diodes you have studied Transistors are more complex and can be used in many more ways They are very important and can be found in almost all modern electronic equipment The name transistor is derived from trans resistor meaning that it changes resistance Unlike a diode a transistor has three leads The three transistor leads are designated as Base
45. de is either shorted or leaky The digital meter can t test 1 because the output from the meter is only about 500mv to 2 volt If a diode breakdown when under full load there is no way to test the diode unless you have a very expensive diode checker or tester which 1s specially designed to track this type of fault Substituting with a known good diode is often the only way to prove that an intermittent diode 1s causing a particular problem Sometimes an intermittent diode could be located using a coolant spray and hair blower Diodes are rated in Voltage and Ampere Refer to semiconductor data book for the exact specification Always replace a diode with the same or higher rating than the original specification Caution Be certain that power is removed from any circuit before performing any of the following diode checks otherwise meter or circuit damage could result Conclusion In order to correctly testing diode you need to use analogue multimeter and set the range to x1 ohm and x10 kilo ohms range With this tips I m sure you will have the confident to check any diodes that comes on your way 66 Testing Bridge Rectifier Using an arrangement of four diodes called a full wave bridge rectifier in a power supply is very common The function of the bridge rectifier in the power supply is to convert the AC supply voltage into DC voltage For full wave rectification it is not necessary to use four individual diodes since all four diodes ca
46. derstand what I meant Dual on off switch Symbol 62 Testing Diode Anode Diode symbol Cathode When comes to testing diode you need a special method to test it If you do not know how to accurately check a diode you will not be able to repair or troubleshoot electronic equipment because a spoilt diode you may think that it is good and you will definitely waste your precious time Diode is label as D in circuit board Usually a rectifier diode can fail in one of the four ways It can become open circuit short circuit leaky and breakdown when under full load An analogue multimeter or digital multimeter can be used to test or check for all the first three conditions except the last one which is the diode breakdown in full operating voltage Diode breakdown when under full load means the diode test okay with your meters but failed when a high voltage flows through it From my experienced in the electronic troubleshooting field I discovered that testing diode using an analogue multimeter is more accurate or precise than using a digital multimeter I could explain to you in details why I preferred analogue meter I do not know about you because I really came across quite a number of diodes where it tested ok with digital multimeter but failed when check with analogue multimeter The first step on how to test a diode accurately is to remove one of the diode lead You can t always be certain if a diode 1s good or bad if you perfo
47. e capacitor is combined with other components in filter or timing circuits Capacitor is symbolized as shown in below and it is denoted by a letter C 41 Symbol of a capacitor Electrolytic Capacitor Unit of capacitance Capacitance is measure in farads F Practically farad 1s a large unit The smaller units are microfarads nanofarads and picofarads microfarad 1 1 000 000 farad nanofarad 1 1 000 000 000 farad 1 picofarad 1 1 000 000 000 000 farad 89 So 0 01uF IOnF 10 000pF Microfarad can be written as MFD MF or uF or simply M Nanofarad is written as NF Picofarad is written as Capacitors rated in picofarads are found in RF and high frequency circuits Capacitors rated in microfarads are incorporated in low frequency and DC circuits like power supplies audio amplifiers and digital and timer circuits Types of capacitors There are basically two types of capacitors 1 e Non Polarized Capacitor Polarized Capacitor a MICA a Electrolytic capacitor b Paper b Tantalum capacitor c Ceramic d Polyester e Polystyrene Non polarized capacitors mean that they can be inserted into a circuit in any orientation While polarized capacitors must be inserted in the proper orientation with respect to applied voltage If the polarizes capacitors 1s connected in opposite polarity it may explode aL High voltage ceramic capacitor Polyester film capacitor Tantalum capacitor Voltage
48. e questions about testing electronic components or even in electronic repair please do not hesitate to email me at jestineyong electronicrepairguide com I wish you all the best and look forward to hearing your success story To your success Jestine Yong Bsc Eng UK Author of Testing Electronic Components http www testingelectroniccomponents com http www electronicrepairguide com http www findburntresistorvalue com http www jestineyong com http www noahtec com 167
49. e ripple The ac transformer linear transformer converts the main line ac voltage to another lower ac voltage and the lower ac voltage will flow to both the diodes The function of the diodes is to convert the ac voltage to DC voltage and the 1000uf capacitor is use to filter off the ripple in the line The clean DC voltage assuming 7 Volts 1s now entering pin 1 of 7805 voltage regulator IC as input voltage Pin 2 1s connected to ground and pin 3 will be the output which is 5 Volts The 0 luf capacitor at the output line again acts as filter to remove high frequency interference Testing Voltage Regulator d EL Li Pa aJ ANE Me lace black probe to ground and _ red probe to input to check the input voltage of voltage regulator SUP aA 1 Place the red probe to out and you can test the output voltage 111 You can t test a voltage regulator IC the same way you test on other components You have to test the voltage regulator with power ON That s right you have to switch ON the equipment in order to accurately test voltage regulator Identify the voltage regulator IC in circuit board first and normally it is label as IC Look at the part number and if it 15 7808 then you automatic know that the input must more than 8 Volts and the output should be 8 Volts Place your digital meter black probe to the equipment ground and the red probe to pin
50. e same or higher voltage and ampere rating d Set to A 10 K Ohms red probe to and black probe to one of the ac pin It should have a reading 68 3 Reverse the probes and it should not show any reading reverse bias your probes to both the AC pins of bridge rectifier It should not have any Again reverse the probes and it should not show any reading 69 e red probe to the other ac pin It should show a reading Reve E us rse the probes and it should not have reading All these are the right procedures to test any bridge rectifiers 70 Testing Light Emitting Diode LED Pp Typical LED Light emitting diode LED is a diode that produces light when current flows through it when it 1s forward bias The LED does not emit light when it is revered biased The LED 15 used as a low current indicator lamp in many types of consumer and industrial equipments such as monitors TV printers hi fi systems and machinery control panels The plastic lens 1s very important in directing and modifying the small amount of light emitted by the LED chip Light can be visible such as red green yellow and white It 1s label as LED in circuit board An LED only needs about 2v across its anode and cathode terminals to make it emit light If a higher voltage 1s used the current which flows through it may be high enough to damage it In order to limit current when an LED is used at higher volta
51. e the meter to blow Don t connect your ammeter meter set to current range directly across a power source such as a battery or power supply output An ammeter must always be connected in series with the load Always treat all electrical circuits with respect Knowing what you re doing is important If you don t know what you re doing in areas that could prove dangerous such as in 240 volt household circuits then don t do it Get more information or just ask a repair friend to show or guide you the right way to test electrical circuits Lastly there are many differences among various makes of digital and analogue multimeters Always study the instruction booklet that comes with a particular meter to ensure you are using it properly and safely 16 How To Test AC DC Voltage AU Ta A AC Voltage test range ic Lo A 50 5 eL FAs 00 DGmA AC DC Voltage ranges in analogue multimeter yer l di M 4 r P d LS F ms A ess button the meter will change o AC Voltage test 17 Analogue multimeters can measure both DC voltages marked DCV or Vdc and AC voltages marked ACV or Vac It is important to remember that all voltage either AC or DC must be measured in parallel with the desired circuit or component Never interrupt a circuit and attempt to measure voltage 1 series with other components Any such reading would be meaningless and your ci
52. ement must be reversed in order to check for PNP type of transistor as shown in Figure 3 Red probeis Black probe Reading in connected is connected ohms to pin no to pin no 1 Low 1 Low 2 High 2 High 3 High 3 High 1 2 3 Figure 3 Identifying a PNP Type of Transistor and pin leads 125 1 Connect the red probe of the multimeter to one of the transistor leads and connect the black probe to any of the other leads 2 If two low readings are found for one connection of the red probe Test no 1 amp 2 while each of the other two position gives two high readings Test no 3 4 5 amp 6 then the transistor 1s PNP type 3 The pin where the red probe 1s connected to showed two low reading when the black probes connected to other two leads shows high reading is the Base In the above case pin 1 is the Base If at X 10 K Ohms still don t show any reading when testing the collector and the emitter pins you have to use your finger to ouch on the base and the centre pin If the pointer moved look at he black probe to see which pin it is pointing to In the above case the black probe is pointing to middle pin then middle pin is he Collector E am If you want to test a PNP transistor then you look for the red probe If possible get some NPN and PNP transistor to test it out irst before checking on the bad transistors 126 Now you must determine which lead is the e
53. en or shorted Zener diode Anode Cathode A wrong part number installed may cause your equipment to malfunction and behave strangely Precious time and money were loss due to that we lack of knowledge in zener diode spec identification If you can t find out what is the code or part number mean then it 1s very difficult to repair the equipment Do not worry as this book here is to guide you to successfully on how to read the zener diode marking 2 4 2 4 Volt zener diode 2V4 2 4 Volt 73 10 10 Volt 10V 10 Volt BZX85C18 18 Volt 1 watt zener diode you have to refer to Philips ECG Semiconductors Transistor Cross Reference Guide BZY85C18 18 Volt 1 2 watt zener diode Note There is also part number such as BZVXX XXX where you have to find it from Philips ECG SEMICONDUCTOR BOOK 1N4746 18 Volt 1 watt zener diode Sometimes a normal signal glass type diode you may think is a zener diode thus you will not get the exact measurement If you have confirmed that the diode you want to measure is zener diode then you can proceed to use my method to accurately test it For your knowledge a zener diode with 2 4 volt to 12 volt should have two readings when test with an analogue meter set to times 10K ohm range But these readings are not shorted reading Cathode Anae A 1N4733A zener diode Let me guide you when you put your meter probes across the zener diode of 2 4 volt using the times 10 k ohm range one way will show
54. er diode 1500 800V 10A 125W BU 2SChecking the SCAN of HOT with the ehelp of Iso 49W BU 25semiconductor data book T BU 25zz m 150 MON LE Euri nii orcoo NE Ci Na D RBU 2522 Iso 45W int Damper Dio There are two types of HOT 1 is without damper diode while the other one is with damper diode How do we know if a particular HOT comes with damper diode or not It s easy check from the semiconductor data book or searches the internet Checking a HOT that does not have the built in damper diode is exactly the same when you are testing a NPN bipolar transistor please refer to the testing NPN bipolar transistor If the HOT have a built in damper diode then you have to follow this way to test it Set your analogue meter to X10 K Ohm and place the black probe to centre collector pin Now moving the red probe touching the first base and the third emitter pin and it should not show any readings If you get even a single reading the HOT 1s considered shorted 144 Dr you can remove the HOT to test it off LPL ard Conclusion If you measure base black probe and collector red probe it should have reading If you measure base black probe and emitter red probe it should have reading you measure collector black probe and base red probe it should have no reading If you measure collector black probe and emitter red probe it should have no reading f you measure emit
55. esults that you get when comparing and checking a good and a bad zener diode It would not take you a long time to become familiar in testing a zener diode accurately One more tip replace only a zener diode with the same or higher wattage If possible use the exact voltage and watt 1f you want the equipment that you repair to last longer Use analogue multimeter to test zener diode 75 Testing Linear Transformer Secondary winding 12 olt ac outomat Transformer symbol Testing transformer is very easy if you follow the procedure explained in this book Generally there are two types of transformer in the market 1 the linear type and the switch mode power transformer In this page I m only explain on how to test the linear transformer I will explain about the switch mode transformer in next chapter Before that I would like you to know what the function of a transformer is The function of a transformer is to change AC voltage A transformer cannot change direct current DC voltage Transformer is label as T in circuit board 76 input mto 9 volt output F 7905 voltaze regulator 1c output 5 volt to the mainboard The power supply section of a VCD player 5 Q3 There are three types of linear transformer 1 Step up transformer to increase the output voltage Typical example 1s 240v ac input with a 480 volt ac output high voltage 2 Step down transformer to decrease the output voltage Typical ex
56. et to X 1 Ohm across the common Com and the normally close NC pin and when you hear the tic sound you will see that the meter pointer will drop from the zero Ohm to infinity 1ndicating open circuit Similarly when you place the probes across the common and the normally open NC pin and when you hear the tic sound you will see that the meter pointer will move up from the infinity to zero Ohms indicating close circuit If you get such reading that s mean the relay 1s working fine If there is no response from the meter pointer won t move even though the relay coil already been connected with the power supply the relay need replacement 165 Technical Books For Reference Bibliography Basic Electronics By Bernard Grob McGrawhill Publication Electronics Principles and Applications By Schuler McGrawhill Publication The Illustrated Dictionary of Electronics By Stan Gibilisco McGrawhill Publication ECG Semiconductor and Master Replacement By ECG Philips Guide Up to Date World s Transistor Diodes By Tech Publication Thyristors amp IC s Comparison Tables Volume I amp II 166 Conclusion With the information you have acquired you should have a basic understanding of how to test almost all of the electronic components found in electronic circuits I strongly suggest you started right away all of the tips and tricks you have learned from this E book If you hav
57. fied further by the second transistor This package provides higher input resistance and a very high current gain such as 10000 Darlington pairs are sold as complete packages containing the two transistors They have three leads Base Collector and Emitter PNP and NPN which are equivalent to the leads of a standard individual transistor There are two types of Darlington transistors one that without a built in diode whiles the other type has a diode in it You have to refer to semiconductor data book to check if the Darlington transistors have a built in diode or not 134 Testing Darlington transistor without built in diode One example part number of a Darlington transistor that do not have a build in diode is the C516 or BC516 If you refer to semiconductor data book it is stated as PNP Darlington transistor BC 509 Si N BC 510 yer g Si N SP s16 P Si P Darl BC517P Si N Darl JL SUI Uni 0 2A 0 36W 200MHz BC 208 fa 508 40V BC 513 50V Uni 30V 2 0 3W 3200MH7Z 513 ra Uni 40V 0 4 0 625W 250MHz B 30k Uni 40V 0 4A 0 625W 220MHz gt 30 Uni 0V 0 054 0 625W gt 100MHz adem SEN pee ve Si N BC 520 45V BC 522 Si N BC 520 Be 523 CAI zu oer ey Checking the transistor data with the help BC 524 of semiconductor book 0 825W BC 5258 From the data book we know thatthe 0 625 BC 526 5161
58. flow between emitter and collector 118 Transistor Heat sink Jm i Te ae 4 mE IE __ j E ea L i m m E The heat generated by current flowing between the collector and emitter junctions of a transistor causes its temperature to rise This heat must be conducted away from the transistor otherwise the temperature rise may be high enough to irreparably damage the P N junctions inside the transistor Power transistors produce a lot of heat and are therefore usually mounted to a piece of aluminium with fins called a heat sink The heat sink draws heat away from the transistor allowing the transistor to handle more power than if there were no heat sink Low power signal transistor do not normally require heat sinking Some transistors have a metal body thus a mica sheet has to be used to prevent the body from touching the heat sink 119 Transistor Failure Transistor can fail in a number of different ways Transistors have forward and reverse current and voltage ratings like diodes do Exceeding either rating can destroy a transistor A bad transistor may short circuit from the base to the collector or from the base to the emitter Sometimes a transistor is damaged so badly that short circuits develop between all three of the leads A short circuit often allows a large current to flow and causes the faulty transistor to heat up The transi
59. ges a resistor must be connected in series with it The cathode of the LED is identified on the package by the flat side on the plastic The life expectancy of LED 1s about 100 000 hours WW flat anode A cathode anode cathode General appearance and Symbol for a light emitting diode 71 Testing LED Remember that the LED only emits light when it 1s forward bias and the LED does not emit light when it 1s revered biased If LED does not emit light when it is forward bias then it has developed an open circuit and should be replaced Power must be off when check the LED Set analogue meter to X1 Ohm and place the red probe to cathode shorter leg and the black probe to anode longer leg The LED Should lit xlohms xlohms LED emits light when it is forward bias b LED does not emit light when it is reversed bias Testing LED with analogue meter 72 Testing Zener Diode REPLACEMENT 2 brg wwe i j ECG Semiconductor Data Book PHILIPS Method of testing zener diode is totally different from testing diode You need an analogue meter to do the job Before you start to test any zener diode you must first understand the marking or part number and then look for the voltage ratings Once you know the zener diode voltage from your favourite data book such as the Philip ECG semiconductor master replacement guide then it is easy to check with your meter to see 1f it leak op
60. h a ringer tester like using the dick smith coil tester Checking the ohms resistance or continuity on a linear transformer is not accurate as compared when using a ringer tester However there 1s still one disadvantage which 1s the winding can go shorted when under 81 full operating voltage even though both windings checks okay with ringer test Conclusion The first method voltage testing is the best choice to test linear transformer accurately but first you must know how transformer work and get an experienced technician s friend to help you out before performing the test on your own For some transformers like the UPS uninterruptible power supply you need wiring diagrams to assist you because there are so many secondary windings and you may get confused Lastly checking switch mode power transformer is different from testing linear transformer I will cover on how to test a switch mode transformer in next chapter Fi A Switch Mode Power Transformer 82 Testing Switch Mode Power Transformer A switch mode power ransformer in power supply section in Computer Monitor Switch Mode Power Transformer SMPT are used in switch mode power supplies in electronic equipment such as Computer Monitor TV DVD and etc The function of SMPT 15 to convert the AC wave to some other value lower or higher The input 1s called primary winding while the outputs are secondary windings 83 Switch mode power transformer rarely b
61. he photo below 159 he specification of Relays 12 Volts LJ 7 T The pin outs of a typical relay cu t 3 Au 160 Normally Open NO ormally close NC Common Coil pnt ems INT EE d The 5 pin outs of a Relay Protection Diode Relay Contacts Switched Collector Circuit Base Emitter Fig 1 basic Relay circuit Battery Load Figure 1 show a basic relay circuit If there 1s an input signal going to the base of transistor the transistor will conduct and the 12V will flow through the relay coil the collector out from emitter and to ground OV This will energize the relay coil and cause the armature to switch from the normally close NC to normally open NO When the armature in the normally open state no current will flow to the lamp load and the lamp will go off There are two steps to test relay first use your analogue meter set to X 1 Ohm and place across the relay coil as shown from the photo in next page This is to make sure that the relay coil 1s not open circuit If it opens 161 circuit there will be no reading registered at your analogue meter A good coil should show resistance 4 sing analogue meter to check the coil of a Relay ERE ES You can test it either way with the probes lliSet analogue meter to X1 Ohm and measure the relay coil The
62. hort with body and it will go off immediately or the supply voltage will drop 122 e Whenever replacing output transistor nut bolt should not be too tight or too loose e Horizontal output transistor with integrated diode should be replaced with the same type of transistor Transistor Testing and Identifying the Leads A transistor can be checked out of circuit with any of the many different transistor testers on the market The suspected transistor can be check out of the circuit with resistance measurement Ohms range from the analogue multimeter Use ohmmeter scale to detect a leaky open or shorted transistor I do not encourage testing transistor with digital meter as l ve encountered many times that a transistor test good with digital meter but failed using the analogue meter Checking transistor with an analogue multimeter An analogue multimeter can be use to perform a basic test on a transistor the diagram in Figure below will help you to identify the base collector and emitter leads for commonly used transistor You should refer to the transistor data guidebook if you are in doubt about the connections of a transistor But if you are about to use a transistor of an unknown type 1 e NPN or PNP the following simple test will give the answer It will also allow you to check a transistor 1f it 15 leaky opens or shorted Set to X 1 Ohm and place the black probe to pin 1 and then place the red probe to 7 and 3 If the
63. in the pointer will not move at all In other words if you test a NPN transistor look for the black probe and if you test PNP transistor look for the red probe If there is no response from the meter pointer won t move even after you have use your finger to touch on the pins then the transistor has developed an open circuit Note For checking PNP transistor perform the same test by reversing the test probe These tests also give some indication of a transistor s condition If the transistor does not check out as describe above there may be something has gone wrong with the part For example if the emitter collector Junction shows a low resistance in both directions at x 10 K Ohms the transistor is shorted The right way to hold a transistor and test it with analogue multimeter For many of you this probably seems like a lot of transistor information to absorb Checking transistor is not as easy as checking the two leads devices like the resistor capacitors diodes and etc In reality this 1s only the surface of a fairly deep subject Experimenting with a few transistors and a multimeter as you go back through the material is 128 an excellent way to gain greater understanding of how to accurately check transistors You can purchase several types of general purpose replacement transistors for less than RM 1 00 each from many electronics suppliers Get a few NPNs and a couple of PNPs grab your multimeter and see for you
64. is breaking down when under load and it can t check capacitors in circuit It s still worth to invest in this meter because it can check almost 80 90 of capacitors failure 100 ELECTROSM DESK S SPECIALS Te ror PAN E opnan i LISCHARGING CHEC KING DCR OCR NORMAL e DER LOW a LC BATTERY Eds Capanalyser 88A Esr Meter The third and most accurate method is to use an ESR meter which stand for equivalent series resistance This is the latest technology in testing capacitors It can only check electrolytic capacitors and the advantage 1s that you can perform capacitor testing while the capacitor 1s still in circuit and have the accuracy of 99 compare to other meters It is fast and can discharge a capacitor before it begin to test the capacitor and save you a lot of time ESR meter is the most reliable and accurate meter that I ve ever invested A Sencore LC103 Capacitor amp Inductor Analyzer 101 If you have the budget you may consider to invest in the high end capacitor tester such as the SENCORE meter LC102 OR LC103 these meters have the capabilities of measuring any type of capacitors with four tests measure capacitor values checking for leakage equivalent series resistance ESR and Dielectric absorption It can test aluminum electrolytic capacitor film capacitor ceramic high voltage capacitor and etc It also has the function to check inductors or coils too A capacitor failu
65. issing half of the display and also erratic Replacing only the crystal solve the OSD problem in Monitor A loosen crystal connection in Computer Motherboard could cause the system to hang after running for sometime On Screen Display Crystals are quite fragile components because of their construction and designed Unlike a resistor or a capacitor if you drop one on the ground from a decent height it s a 50 50 chances whether it will function again 153 Though crystal don t become faulty easily like a resistor or capacitor it 1s important for an electronic repairer to know how to test a crystal CUT mcm EMG 3000A 322 MN __ i i 3 58 crystal in 1 monitor malin SE 1 hoard Lan A Crystal and its location marking in a Computer Monitor Testing the crystal 1s not a breeze either You cannot just take out your trusty meter and test the crystal in it In fact there are three methods to test a crystal Using an Oscilloscope A crystal oscillator produces a sine wave when excited It is appropriate then to see a waveform representative of a sine wave on the clock pins If the clock is not working properly replace the crystal Test the crystal with power on Place the scope black probe to cold ground and the main probe pin to the crystal pins Normally microprocessors are usually very reliable but not in this case of a Compaq MV720 Monitor Monitor came in with
66. it 105 Testing Ceramic Capacitor The ceramic capacitor leakage quite often happened when there 1s a high voltage applied into it Under normal testing with a digital capacitance meter or an analogue meter will not revealed any symptoms and you may think that the ceramic capacitor that you checked 15 ok If you skip that capacitor the chances for you to repair the equipment are very slim In computer monitor the ceramic disc capacitor and high voltage resin coated type 1s frequently found in the power supply high voltage and cathode ray tube monitor area When it fails it can cause erratic or intermittent problem to the monitor such as blinking display no display missing one of the colour bar and etc Resin coated ceramic disc capacitors Using analogue and digital capacitance meter won t accurately test the ceramic capacitor failure even out of circuit A ceramic capacitor leakage in electronic board can pull down the voltage and cause a lot of intermittent problem to the equipment I will explain to you my true life experienced about this type of capacitor In computer monitor Cathode ray tube CRT board the screen line G2 has about 200 to 600 volt The ceramic capacitor in the screen voltage line is usually rated at 102 103 and 472 and voltage rating of Ikilovolt to 2 kilovolt If this ceramic capacitor dielectric breakdown it can pull down the screen voltage to a very low level and causing no display or picture There 1s n
67. lesting Electronic Components aap lull Brought to you by Jestine Yong http www ElectronicRepairGuide com http www TestingElectronicComponents com http www FindBurntResistorValue com http www JestineYong com You cannot give this E book away for free You do not have the rights to redistribute this E book Copyright All Rights Reserved Warning This 1s a copyrighted material no part of this guide may be reproduced or transmitted in any form whatsoever electronic or mechanical including photocopying recording or transmitting by any informational storage or retrieval system without expressed written dated and signed permission from the author You cannot alter change or repackage this document in any manner Jestine Yong reserves the right to use the full force of the law 1 the protection of his intellectual property including the contents ideas and expressions contained herein Be aware that eBay actively cooperates in closing the account of copyright violators and assisting in the legal pursuit of violations DISCLAIMER AND OR LEGAL NOTICES The reader is expressly warned to consider and adopt all safety precaution that might be indicated by the activities herein and to avoid all potential hazards This E book is for informational purposes only and the author does not accept any responsibilities or liabilities resulting from the use of this information While every attempt has been made to verify the i
68. ly are HOT g Use only plastic screwdriver for shock protection during service operation 2 Discharging Switch Mode Power Supply SMPS Capacitors Most SMPS have a resistor to drain the charge in the main filter capacitor But some resistors may fail and the capacitor can hold this charge even after you have turned off the equipment This capacitor has a range of about 150uf to 330uf at 400 working voltage Before you start to work on a power supply always turn off the power and discharge the capacitor You can do this by placing a resistor across the two legs of the capacitor The resistor value can be around 2 2 to 4 7 kilo ohms 10watt It takes only a few seconds to fully discharge a capacitor Double check the capacitor with a voltmeter after every discharge I will cover more details in the capacitor topic on how to discharge capacitors NOTE WARNING Do not discharge capacitor with screwdriver because i It may melt the tip of the screwdriver It will damage the capacitor and its terminal ii If we are too near to the point of discharge the heavy spark generated may cause injury to our eyes eA Hot Ground Problem Hot ground is the switch mode power BB 2 supply ground negative 4 it ie cx m Me Supply Area Modern equipment consists of two grounds one of which is a hot ground while the other is a cold ground Hot ground is in the primary side of a switch mode power
69. me except that the ohms range instead of starting at 00 should now start at 10 Here is some of the simple calculation to determine the meaning of the code printed on the variable resistor 12 100 100 ohm 13 1000 1000 ohm Kilo Ohm 54 50000 50000 ohm 50 Kilo Ohm 102 10 00 1000 ohm 1 Kilo Ohm 203 20 000 20000 ohm 20 Kilo Ohm 523 52 000 52000 ohm 52 Kilo Ohm Testing Preset 20 Kilo Ohms 203 Preset These are miniature versions of the standard variable resistor They are designed to be mounted directly onto the circuit board and tuned only when the circuit 1s built For example to set the colours of Computer Monitor by turning the preset in the Cathode Ray Tube CRT board A small plastic screwdriver or similar tool 1s required to adjust presets 48 Presets are much cheaper than standard variable resistors so they are sometimes used in electronic projects where a standard variable resistor would normally be used Testing preset is exactly the same procedure as when you are testing the variable resistor Preset symbol Plastic screw driver p 3 al 2 ii v A Colour preset in Computer Monitor T Smeg s 1 Using plastic screw driver to adjust the preset 49 Testing Fuse Typical example of fuses It s very easy on how to test a fuse Fuse 15 a very thin wire which either melts or vaporizes when current flow through it
70. ment your meter black probe must connect to the chassis as shown in the photo below The red probe then can be use to touch on the DC voltage points Note you must have a good understanding about electronic circuit and safety before you do any voltage testing on electronic equipment In order to perform voltage testing set you digital neter to dc range and place the black probe to 21 itage by connecting the black probe o HOT ground You should connect it supply the black probe have to connect to HOT ground onnecting the black probe to cold ground may blow ur meter or you may not get an accurate result 22 LIMEN j i HOT ground gt m I the right way to test voltage at primary side Connect the black probe to HOT ground Warning A switch mode power supply has primary and secondary section In order to check secondary voltage the meter s black probe have to connect to cold ground chassis ground and if you want to test on the primary voltage the black probe have to connect to primary ground If you are not familiar of what I am saying please ignore this test or get a repair friend to assist you 23 How To Perform Current Testing E Analogue meter do not have the AC current Test Only DC D B au BW ji current p A 1 ES _ In most electronic troubleshooting and repair you will rarely take current measurements Most general purpose digi
71. mitter and which is the collector Assuming you are checking an NPN type of transistor and you already know that lead number 1 is the base and now you must determine which lead lead 2 or 3 is the collector First set your multimeter ohm s range to x10kQ Connect the test probe according to the diagram shown in Figure 4 Test Black probe Redprobeis Reading in No isconnected connected to ohms to pin no pin no 1 2 3 High 2 3 2 NOTE Certain Transistor might showed high reading on both test either way Figure 4 Identifying the collector lead of an NPN transistor 1 Look for the high ohm reading Test no 1 and see which lead the black probe 1s connected to 2 From Figure 4 the black probe is connected to lead 2 and this lead is the Collector and lead 3 15 the Emitter 3 Some transistor will show two high ohms readings and if it is the case you should use your finger to touch on the base first pin and the middle pin while you are still holding the probes on the transistor middle and the third pin Assuming while your finger touching the base and the middle pin the pointer show some resistance then looks at the probe If it 1s the black probe on the 127 middle pin then the middle pin is the Collector If middle pin is the collector the third pin must be the Emitter If the red probe is on the middle pin touching your finger between the base and the middle p
72. mon Switch symbol button de i he 4 This is how you test ON OFF switch Place Ph switch Set to X 1 Ohm and if you press the switch button the pointer will move up If no There are many type of switches in the market some are on off mechanical switch while some are micro switch The function of the switch 1s to act as a contact between two points either to let current flow or to stop it It is very easy to test switches just set your meter to X 1 ohm and place your meter test probes to either leg pin Now press the switch and you should see the meter s pointer shows zero ohm 60 switch button was pressed for a good switch you will hear a sound from the meter j i If after pressing the switch and nothing happen suspect a bad switch similarly you can use a digital meter set to buzzer sound to test a switch A good switch with a good contact should make the digital meter to produce the buzzer sound No sound means the switch 1s defective 61 Some switches have dual on off contact and is called double pole single throw switch DPST A DPST switch is often used to switch mains electricity because it can 1solate both the live and neutral connections Testing the DPST switch 1s relatively simple test the contact at one time before you test on the other contact Testing method 1s the same just as when you are testing the single on off switch above Look at the photos and should un
73. multimeter set to times 10K ohm range to check it Assuming you are testing the n channel mosfet then put the black probe to the drain pin Touch the gate pin with the red probe to discharge any internal capacitance in the mosfet Now move the red probe to source pin while the black probe still touching the drain pin Use your right finger and touch the gate and drain pin together and you will notice the analogue multimeter pointer will move forward to centre range of the meter s scale Use your finger to touch on the gate and drain pin Lifting the red probe from the source pin and putting it back again to the source pin the pointer will still remain at the middle of the meter s scale To discharge it you have to lift the red probe and touch just one time on the gate pin This will eventually discharge the internal capacitance again 131 At this time use the red probe to touch on the source pin again the pointer would not kick at all because you have already discharge it by touching the gate pin These are the good mosfet characteristic You need to practice more by taking some FET from your bench or from your component s compartment Once you know the secrets testing other mosfet is as simple as testing diode Testing N cannel fet place black probe to center pin 2 and red probe to pin 3 Now use your finger to touch on pin 1 and 2 the meter pointer should show some esting P channel fet place red probe to center pin 2 and
74. n be obtained in one package as shown in Fig 1 Each package has two AC input terminals and two Dc output terminal marked and Typical Bridge Rectifier Observe the marking and AC A schematic for the full wave bridge rectifier 1s drawn in Fig 2 Bridge rectifiers are classified in the same way as single diodes 1 by their maximum reverse voltage or Peak Inverse Voltage PIV and Forward Current IF It is label as BR in electronic circuit Ja l 2 m a b c Fig 1 Some examples of bridge rectifier Fig 2 Schematic for diodes wired as a a marked b in line c dual in line DIL full wave bridge rectifier 67 Testing Bridge Rectifier Set your analogue meter to X 10 K Ohms and place your meter probes to and ac pin It doesn t matter which probes to which pin but as long as it won t show two similar low resistance reading registered by your meter when you reverse the probes it is okay It should have only one reading Next again place your probes to the and to another AC pin there are two AC symbol in bridge rectifier and should have only one reading even though you had reversed the probes Similarly when you want to test the negative with the first AC and then negative with the other AC Look at the photos and you should understand it Assuming when you found one of the diode shorted in the bridge rectifier you have to replace the whole package Replace it with th
75. n board too Set your analogue meter to X1 ohm and place the probes across the small coil The meter should show some reading or continuity and this proved that the coil winding is okay Small coils seldom spoilt because it have less winding compares to big coils where it could have many turns of winding and chances for it to go shorted between windings is very high small coil can be test with an analog rmiltimeter 56 Testing bigger coil or inductor such as the computer monitor B coil you need an inductance meter to find out the exact inductance value which is in the unit of Henry h From experienced using an inductance meter to check coils to see if it good or bad is not recommended because a shorted coil shorted between winding could have a good inductance value and you would miss out checking a bad coil Unless you want to use the inductance meter to calculate the reading and do rewinding looping and etc on that coil I would only test a big coil with dick smith flyback meter Any shorted winding in it could be easily detected by this meter A bigger coil canbe check with an inductance meter Above reading shows 105 3 nucrohenry 57 ow is the time to share my true case example a computer dealer send me a monitor for repair with power blink symptom Usually I do not straight away repair the onitor but I would first use the flyback tester to scan all the ajor coils switch mode ransformer
76. ne and replaced with a good working component I eventually found the caused of the power supply problem Guess what It was the main power filter capacitor problems 220 microfarad 400 working voltage After replacing the filter capacitor the fuse would not blow when switch on and the power supply worked perfectly fine I begin my detective work to explore why this particular capacitor can caused the fuse to blow even though the filter capacitor already confirmed working with all my faithful meters The meters that I used to test the filter capacitor were analogue multimeter digital capacitance meter and the famous ESR meter I assumed that many of you who read this book already know how to perform capacitor measurement with all the meters I ve just explained in previous section Using an analogue meter to measure this filter capacitor showed capacitor is charging and discharging meaning the pointer will flick up and then gradually goes down test with a digital capacitance meter showed around 220 microfarad still within the capacitor tolerance range and with the most powerful electrolytic capacitor tester which 1s the ESR meter it showed a low ESR reading which 1s also a good reading Then how do I know if the filter capacitor is faulty since all the meters tested ok on the filter capacitor What I ve checked on the filter capacitor is just the value ESR and the charging and discharging test but another test you should not miss out
77. nformation provided here the author cannot assume any responsibility for any loss injury errors inaccuracies omissions or inconvenience sustained by anyone resulting from this information Most of the tips and secrets given should only be carried out by suitably qualified electronics engineers technicians Please be careful as all electrical equipment is potentially dangerous when dismantled Any perceived slights of policy specific people or organizations are unintentional If you have any information regarding the illegal reselling or duplication of this E book please report it to jestineyong electronicrepairguide com for your reward This book 1s dedicated to my wonderful wife Michelle Without her loving encouragement and support this book would still have been possible but not nearly worth the trouble Iz AICLY VISE oree x e OueR e POI Ee EPI eU DU DE 6 2 Understanding Analogue and Digital Multimeter 13 3 How To Test AC DC Voltage ee eee 17 4 How To Perform Current Test eee 24 5 Continuity cos see EUER EEEO 28 6 Resistance and Resistors eee eee eee een 30 7 Resistor Colour Code Calculation 32 So T s ng R SISLOE ooo vest Por UNES Cures 37 9 Testing Variable Resistor ecce eee eene e enn 45 TU Tesne ooi erre oaa Uv eiua
78. no high voltage symptom Using the scope to check on the crystal revealed very unstable waveform and replacing the microprocessor solved the no high voltage problem and the crystal waveform shown a perfect sine wave 154 black 48 probe to ground T3 T EI Li _ Using oscilloscope measuring Computer Monitor Crystal How to measure crystal frequency with oscilloscope Second method is to use frequency counter to check the frequency of the crystal oscillator The measurement must be taken when the equipment power 15 On Put the probe of the meter or frequency counter to the crystal pin and read the measurement That s mean place the black probe 155 to cold ground and the red probe to the crystal pins Make sure your frequency counter meter has the range that 1s higher than the crystal frequency you are checking If the crystal is 8 MHz then your meter should have the range to be able to check that frequency Assuming the readout of the crystal is 2 5 MHz then you know that the crystal 1s not functioning well and need to be replaced Normal digital multimeter usually has a small range for checking frequency However the digital meter Greenlee brand that I m using is able to measure up to 24 MHz You can read the specification of your meter manual and see how high 15 the range 1s Frequency counter in a digital multimeter 156 PEN ciem Jin ee M a6 ore A 1 17 a w Me
79. o way for an ohmmeter with 12v output and a digital capacitance with 3v output to accurately check the ceramic disk capacitor that have the voltage rating of 1 2 kilovolt or even 3 kilo volt in certain types of circuit 106 such as the inverter circuit in LCD monitor So the right way to check the ceramic capacitor leakage 1s to use an insulation tester If you have the analogue insulation tester or meter the meter panel will show a short circuit when certain voltage are applied to check the ceramic capacitor dielectrics or materials The voltages that you can select 15 depends on the brand or model you had Some have the range of 50v to 1000v and some have the range from 100v to 5000v It is optional whether you should have one If you have one then it would be an added advantage to you The other option that you have is to direct replace the suspected failure ceramic capacitor In my country you can get a new one in less than US150 or you may bid a used unit from eBay Sometimes you don t need any meter to test the ceramic disc capacitor because the burnt marked in its coating already proven it has gone through some serious heat or high temperature and need to be change A IN SUERTION TESTER A Kyoritsu Insulation Tester You may also sometimes see cracking in its body Ceramic capacitor does not have polarity and when you need a replacement get the exact or higher voltage rating with the same capacitance value 107
80. or terminals This could cause eye injury burns or secondary injury When in doubt take time to discharge power supply capacitors before working on a piece of equipment Be sure to connect electrolytic capacitors in the right polarity 1 e negative to negative and positive to positive If the electrolytic 1s connected in opposite polarity the reversed electrolysis forms gas in the capacitor It becomes hot and may explode This 15 a possibility only with electrolytic capacitors How to read capacitor numeric code The non polarized capacitor of nominal value of less than 1000pF 15 usually plain marked For instant for a 220pF capacitor it will be marked 220 only For capacitance values of 1000pF or more a three digit code is used The first two digits represent the two significant digits and the third digit represents the decimal multiplier For instance 102 represents a capacitance of 10x10 1000pF and 104 represents a capacitance of 10x10 100000pF 0 1 uF Basically it has the same calculation method as resistor 91 224 47uF Ceramic disc capacitor Example 1 What is the capacitance value of these capacitors that marked 22 gt 330 gt 471 gt 562 gt 103 gt 224 gt microfarad g 335 gt 22 picofarad 330 picofarad 47x10 470 picofarad 56x10 5600 picofarad or 5 6 nanofarad 10 10 10000 picofarad 10 nanofarad 22x10 220000 picofarad or 220 nanofarad or 22
81. r reverse bias the diode is considered open circuit The real problem when testing a diode using the diode test function of a digital meter is that an open or leaky diode the meter sometimes reads okay This 1s due to the digital meter diode test output voltage which you can measure the output test probe using another meter is around 500mv to 2v An analogue meter set to x1 ohms range have output about 3V remember the two 1 5V batteries you installed 1 the analogue meter The voltage 1s adequate to show you the accurate reading of a diode when under test Even if you have a good reading at x1 ohms range checking a diode this doesn t mean that the diode is good 65 P m Cm Tg j Now set your meter to X 10 K Ohms range and place the black probe to cathode and red probe to anode good working diode should not show 3 any reading sir You now have to select your meter to x10Kohm range to test the diode again The output voltage of x10k ohms is about 12 Volt remember the 9 volt battery in your meter 1 5 volt 1 5 volt 9 volt 12 volt Again the diode under test should show only one reading This is exception to Schottky diode where it has two readings but not shorted reading I will explain how to test Schottky diode in the next section If the meter showed one reading then the diode under test is good If it has two readings then most probably the dio
82. rcuit may not even function If you are unsure of what range to use start with the largest range to prevent possible damage to the meter To check the 9 Volt batteries I ve selected the 10 DCV range as shown below i d n 1 y Ta 2 DRY BATTERY 59V GF22 al 1 4 Lu cun ELECTRK APPLIANCE i WADE P CHINA E Look at this range malf you select the 10 DCV esting a 9 Volts dry cell battery Red probe to positive and Black probe to negative There s no need for calibration in voltage testing 18 Set to 250 V ac to test i230 V ac the main outlet voltage 230 V AC Either way you connect the test probes the result was still the same bserve the test probes The result s still the same 230 Volts even 19 In order to accurately test AC and DC voltage I only use the digital meter as it shows more precise reading than the analogue meter Set your multimeter to its appropriate function DCV or ACV then select the proper range Note an auto ranging digital meter will select its own range Place your test leads across in parallel with the part under test as shown in all the photos below and read voltage directly from the panel meter It is very accurate to use digital meter to test voltage 20 Digital meter is accurate too to test on AC Voltage How to take voltage measurement in electronic equipment If you want to test voltage in electronic equip
83. re numbered 2N for example 2N3904 2N3906 and etc The 120 first digit is the number of junctions However Japanese transistors have different type numbers The following designations are generally used number Type frequency frequency frequency O S deme oe frequency P Channel FET 2SJ306 J306 N Channel FET 2SK792 K792 Note that S is used to indicate a semiconductor If you found a transistor with the part number of C945 you will immediately know that it is a NPN transistor A NPN Transistor 121 A PNP transistor Points to remember when replacing transistor with substitutes Polarity of the transistor 1 e whether it is PNP or NPN Substitute transistor should have almost same voltage current and wattage rating Whether transistor which is being replaced is of low frequency or high frequency type Whenever replacing transistor see that base collector and emitter are soldered in their proper position While replacing transistor desoldering pump must be used and soldering iron should not be kept for longer time it may damage the transistor as well as printed circuit board Transistor used for output circuit must have proper heat sink If supply is given without heat sink the transistor may get damaged Whenever replacing horizontal output switching output or power output transistor it should be kept in mind that mica sheet being used should not be broken otherwise output transistor collector will s
84. re when under load 1 very rare Using ESR capacitor meter alone can solve most of the electrolytic capacitor problem 102 Testing Capacitors That Breakdown When Under Full Operating Voltage Testing capacitor breakdown when under full load or voltage only can be done by using special meter Normal digital capacitance meter and analogue meter can t test this type of failure Have you encountered power problem where when you switch on the power supply the fuse blow immediately You have measured all the components in the power primary and secondary area and all the components seem to be working Where 1s the culprit A fuse blown into dark colour were usually caused by lightning strike a shorted bridge rectifier defective Posistor 1n computer monitor and TV circuit a shorted power transistor or FET field effect transistor shorted primary winding in switch mode power transformer shorted secondary output diode and etc A Filter Capacitor in Switch Mode Power Supply I m frustrated as to where be the cause of the power problem Every time when I switch on the monitor the fuse will blow immediately the fuse became dark colour and this indicates that there is a major short circuit in the power supply section or surrounding area which I ve already mentioned above I have tested all the components in the power supply section and can t find the cause of the problem Then I began to 103 substitute all the suspected parts one by o
85. reakdown and if it breakdown it will usually cause power section components to blow or totally blow up the main fuse and trip the ELCB Earth Leakage Circuit Breaker If a SMPT failed normally it was the primary winding shorted The secondary windings are very robust and seldom have problem In order to accurately test the primary winding one cannot use the multimeter resistance Ohm test as it was not accurate and will give a false reading In other words a shorted primary winding will test good with ohmmeter but failed when test with coil tester The famous coil tester 1s the Dick smith flyback tester You can build the flyback tester by visiting this website http www flippers com pdfs k7205 pdf Study the manual and you will definitely know more about coil measurement and other useful information 84 Testing SMPT in Power FET If this pin is negative 39 the other pin must be positive mode Mi power transformer a a No 85 winding of switch mode Wer transformer 18 E Follow the filter positive pin and you will reach one of the point of transformer Now trace rom the center pin of power fet to transformer pin Once you got these two pins location these two pins 4 actually is the primary winding of switch mode power transformer First you must find the primary winding of the SMPT It is very easy by simply referring to the photo given Look at the positive
86. rm in circuit test because of back circuits parallel connection through other components 63 To be absolutely sure you will need to lift or disconnect one diode lead from the circuit to avoid back circuits Unless you are very sure about the board you are checking Sometimes I do found bad diodes when checking it on board Your experienced will tell you when to test a diode on board or off board If you are a beginner I highly suggest that you measure a diode with a lead removed from the board to avoid any confusion results from your meter om lt node Cathode ne at m 1 m Forward bias test set to x 1 Ohm and place the red probe to cathode and black probe to anode The pointer should move and show some low resistance If you reverse the probes the pointer will not move at all 64 Set your analogue meter to x1 ohms range to check for current diode leakage reverse and forward testing Connecting the red probe of your meter to the cathode and black probe to the anode the diode 1s forward biased and the meter should read some value of resistance Touch the black probe of your meter to the cathode and red probe to the anode the diode is reverse biased and should look like an open reading the meter pointer not moving If you get two readings then most probably the diode is shorted or leaky and you should replace it A diode test function If you don t get any reading either forward o
87. rself With some actual hands on activity it won t take you long to become confident performing a basic transistor test If you have a budget you may buy specialized transistor tester where you clip 3 of the tester wires to the three pins of any transistors After analyzing it will prompt to you which leg 1s the base collector and emitter and also it will tell you if the transistor 1s good leaky or completely shorted 129 Testing Field Effect Transistor FET or Mosfet D F E Typical example of N channel fet N channel P channel D D S S Mosfet symbol The right way of testing mosfet transistor is to use an analogue multimeter Mosfet stand for Metal oxide semiconductor field effect transistor or we just called it FET Switch mode power supply and many other circuits use FET transistors as part of a circuit Mosfet failure and leakage are quite high in a circuit and you need to know how to accurately test it FET is label as Q in circuit board 130 Measuring component s that have two leads such as the resistors capacitors and diodes are much easier than measuring transistor and FET which have three legs Many electronic repairers have difficulty especially checking the three leads components First find out the gate drain and source pin out from semiconductor replacement book or search its datasheet from search engine Once you have the cross reference or diagram for each pin of the mosfet then use your analogue
88. sadvantage is that you must be very careful when checking it especially when the power 15 on Make sure you have someone to guide you or else you can try the second method P E pow i D y Pip NS LA BIN 5 0 i Checking the primary winding resistance with an alog rmiltumeter EE E CU T fe M rw wp 79 4 ES the venstengsaf the secon winding with an analog meter Set your meter E to X 1 ohm With power off remove the transformer from the board and perform a resistance or continuity test on primary and secondary winding as shown on the picture of transformer below If there is no resistance or ohms reading on the primary and secondary winding measured suspect an open winding and the transformer need to be replaced The advantage of this method is you are safe because no power is applied to the transformer The disadvantage is checking the resistance for ohms reading is not as accurate as when you perform a ringing test mentioned on the third method A shorted primary or secondary winding is still checked well under resistance tests However the good news is when either the primary or secondary winding developed a short circuit it will usually produced a bad smell and the transformer gets very hot on its core or casing 80 hecking the primary winding resistance with a digital nmltumeter The primary winding Perform a ringing test wit
89. stors also can developed open circuit between base to collector or base to emitter The first step in identifying a bad transistor is to check for signs of overheating A bad transistor may appear to be burnt or melted When the equipment is switched off you can touch the transistor to see 1f it feels unusually hot The amount of heat you feel should be proportional to the size of the transistor s heat sink If the part has a large heat sink you can expect it to be too hot but not until the extend of burning the hand or fingers If the transistor has no heat sink yet is very hot you can suspect a problem DO NOT TOUCH A TRANSISTOR IF IT IS PART OF THE CIRCUITRY THAT CARRIES 240VAC Always switch off the equipment before touching any components Transistor Replacement If for some reason you can t get the exact replacement refer to one of the transistor substitution guides and try to identify a near replacement Beware however a substitution guide will sometimes list a replacement for your part even though the two parts are not very similar The important parameters are e Voltage e Ampere e Wattage The replacement part should have a voltage ampere and wattage rating equal to or higher than the original The best is to get an exact part number for transistor it s worth the trouble TRANSISTOR SPECIFICATIONS Diodes are numbered 1N for example 1N4148 1N4007 1N5408 and etc Transistors a
90. t for analogue multimeter which can quickly be destroyed when too much current flows through them for even a very small amount of time Even if you are an experienced repairer sometimes we do made mistake by accidentally touching the probe to the testing points where it should not be touch The slow blow fuse has a coiled construction inside the glass Slow blow fuses are designed to open only on a continued overload such as a short circuit The function of the coiled construction 1s to stop the fuse from blowing on just a temporary current surge Don t replace a slow blow fuse in place of a fast acting fuse because it may not open fast enough to prevent components damage under a high current condition It s not dangerous to substitute a slow blow fuse with a fast acting fuse but it will probably open up unnecessarily every now and then when the equipment 15 first switch on such as when you switch on a Computer Monitor oy LI A blown fuse can indicate how severe the short circuit 1s There s a secret for you a blown fuse can indicate something about the problem If the glass case of the fuse appears clear or transparent and if you can still see the slight broken pieces of the fuse element this means that there s no major short circuit in the circuit Replacing the fuse with 51 one of the same type and rating usually will bring the equipment back to life again However sometimes a replacement might blow the fuse right aw
91. tal multimeters allow you to measure AC current ACA or Iac and DC current DCA or Idc in a circuit although there are often few ranges to choose from Normally analogue meter do not have the AC current range As with voltage measurements current is measured in a working circuit with power applied but current must be measured in series with the circuit or component under test 24 Digital DC current Test If you press the blue button the meter ill revert to AC current test Inserting a meter in series however is not always an easy task In many cases you must physically interrupt a circuit at the point you wish to measure and then connect test leads across the break Although it may be easy to interrupt a circuit keep in mind that you must also put the circuit back together Set your multimeter to the desired function DCA or ACA and select the appropriate range If you are unsure about proper range set the meter to its largest range Make sure that the meter can handle the amount of current you are expecting Turn off all power to a circuit before inserting a current meter as shown in Fig below Insert the meter and reapply power Read Current directly from the panel meter 25 Power supply or battery source Circuit under test a Measuring power supply current Measuring Currents Wrong way to do current test You must remove the path in order to o a right current test 26 Ammeter so
92. ter black probe and base red probe it should have reading If you measure emitter black probe and collector red probe it should have reading Overall a good HOT should have 4 readings and if you get 5 or 6 readings the HOT is considered shorted 145 Testing Silicon Controlled Rectifier anode b cathode gate SCR symbol Anode Typical SCE part mmber Testing SCR silicon controlled rectifier can be done by using an analogue multi meter or specialize tester such as the Peak electronic atlas component analyzer http www peakelec co uk designed to check semiconductor devices easily SCR can be found in many electronic circuits Part numbers such as the FOR3G and MCR 100 6 were very common used in computer monitor Some called SCR as thyristor but in actual fact the word thyristor should not be associated exclusively with the silicon controlled rectifier It 15 in fact a general name given to all four layer PNPN devices including the commonly used SCR The diac the Triac and the SCS are the other popular devices belonging to the family of thyristors SCR consists of three pin of Gate G Anode A and Cathode C In order to identify the pin out one must find it from semiconductor data 146 book such the famous Philips ECG master semiconductor replacement guide The data book will list out the general specification of the SCR such as the volt and ampere You may go to google com search engine and key in the part
93. ter red probe to Meter black probe to either one ofthe On ground Crystal Oscillator i A Crystal oscillator and microprocessor CPU in a main board 157 Third method is to use a Crystal Checker With this way normally the crystal is placed in the feedback network of a transistor oscillator If it oscillates and the LED 1s lightening up this means that the crystal 15 functioning If the crystal doesn t work the LED will goes off Instead of using LED as indicator some other expensive crystal checker uses a panel meter to indicate if the crystal 1s functioning or not If you search crystal information on the internet you will find some websites that provides tips on how to test crystal as well as how to build one You may build simple crystal tester by going to this website http www nuxiel com guides crystal tester html 158 Testing Relay 3 x cx i T K i EC L UR E TT 1 4 TEM amp 25 ypical Relay found in electronic circuits Dp A circuit symbol of relay An electromagnetic relay is basically a switch operated by magnetic force This magnetic force 1s generated by flow of current through a coil in the relay The relay opens or closes a circuit when current through the coil 15 started or stopped The specification of relay normally are 5V 12V 18V 24 V and etc and with amperes rating too All these specification you could see printed on the relay body as shown in t
94. ter sometimes the overall film can wear away that which the wiper cannot make a good contact at certain points The poor contact can cause all types of erratic or intermittent operation If the intermittent connections are due to dust and debris using an electronic oil based contact cleaner may help to solve the problem But if the problems are caused by the wearing away of the resistive film the only option is to replace the variable resistors Use the Philips oilbase contact cleaner 0 service a Variable Resistor 46 You can check the variable resistor resistance with analogue multimeter set to ohm s range as shown in Fig 1 below a b Fig 1 Testing a variable resistor with a analogue multimeter If you measure pin 1 and 3 you will get the variable resistor Ohms reading Now use either one probe to touch pin 1 and 2 Fig a of variable 47 resistor while the other probe touching pin 3 Turn the knob clockwise and anti clockwise to see the changing of resistance The meter should show a smooth reading If the reading is erratic the pointer will moved intermittently You can service or replace the variable resistor Say if the variable resistor is 10kQ the ohms the value should vary from 00 to 10kQ or 10kQ to 00 as you turn the knob clockwise and anti clockwise Now using the probe that touches pin 3 short to pin 2 Fig b while the other probe connects to pin 1 test for the result The reading should be the sa
95. the panel if the pointer flick up and comes down or not this represent charging and discharging If it still cannot flick or no response then set your meter to time 10 ohm and then to Ik ohm and lastly to 10 kilo ohm range First discharge the capacitor before testing it with meter 98 If 1t still don t flick then the capacitor under test have developed an open circuit This 1s a rather old method to test capacitors because even though a capacitor can charge and discharge this does not mean the capacitor value is good Due to this problem digital capacitance meter was developed A Digital Capacitance Meter 99 microfarad capacitor Set to 2000uf if I uf capacitor Testing electrolytic capacitor with digital capacitance meter The second method to test capacitor 1s to use digital capacitance meter and is a little more accurate compares to analogue multimeter Connect the test probe to the capacitor and read the result from the meter LCD display Example a 100 microfarad should have the reading of somewhere 90 microfarad to 120 microfarad Remember capacitors have tolerance just like resistors Be sure to discharge capacitor first before testing A reading of 60 microfarad means the capacitor has lost its capacitance and need to be replaced This meter is more expensive than analogue meter Somehow digital capacitance meter have its own disadvantage which 15 it can t check capacitor that
96. to a painter In this chapter you will learn the features of analogue and digital multimeter and in the following chapters you will learn how to measure electrical voltage current and resistance Learning how to connect a meter and read these electrical circuit values 1s a fundamental skill that every electronics repairers must know in order to successfully perform basic tests troubleshooting and repairing Meter s Function and Range Lem M Adjuster for calibration purposes SAC Voltage range HL L S0uA k o r 29 Positive probe Negative probe Current Ohms or RED colour Black colour range Resistance range ce Analogue and digital multimeters have either a rotary selector switch or push buttons to select the appropriate function and range Some Digital Multimeter DMMs are auto ranging they automatically select the correct range of voltage resistance or current when doing a test However you still need to select the function 14 First just before you make any measurement you must know what you are checking If you are measuring voltage then select the AC 10V 50V 250V or 1000V or DC 0 5V 2 5V 10V 50V 250V or 1000V range If you are measuring the resistance select Ohms range Rx1Q Rx10 2 Rx100 Rx1k 2 or Rx10kQ If you are measuring the current then select the appropriate current range DCmA as shown in the photo in the previous page LCD Display Frequency Test
97. to the two points of the resistor as shown in the photo It doesn t matter which probes to which two points because resistor does not have polarity positive and negative like a battery You should get somewhere near 47 ohm by observing the pointer 38 pinter point to about 47 ohm Analoque meter checking a 47 Ohm resistor If you get more than 47 ohm say 150 ohm this mean that the resistor has gone up in resistance and need replacement If it doesn t show any reaction after putting the probes across the two points of the resistor then we can conclude that the resistor has open circuit bad Remember to press a little bit hard on the leads of the resistor while measuring it otherwise you may not get a precise reading or intermittent reading could occur 39 similarly if you want to check a 15 K ohm resistor short the two probes together and calibrate by adjusting the adjuster knob You have to set your meter to ohm range so that the measurement is within the range Using the X1 Ohm range to test a 15 K Ohm resistor won t cause the pointer to move at all Even 1f the pointer can move it will only move a little bit higher only ull IL ili If you want to test a 15 k ohm resistor then set to higher range and calibrate first by turning the adjuster to make it zero ohm From there only you est the resistor for accuracy 40 a fry Once calibrated you can test on the 15 k Ohr
98. urce R Load resistance b Simplified circuit E T qm DUE 1 i b d The pin had been removed perform current test you iust remove the path and onnect the dc current meter Caution Never try to read current in parallel Placing a current meter in parallel can cause a short circuit across a component that can damage the part the circuit under test or your multimeter 2 Continuity Test Short your meter probes and adjust the adjuster calibration so that the pointer vvill go to zero ohms Continuity or short circuit test Continuity checks ensure a reliable low resistance connection between two points For example check the continuity of a cable between two connectors to ensure that both ends are connected properly Set your analogue multimeter to a low resistance scale X1 Ohms short touch the red and the black probes together the pointer will go to zero ohm If it is not zero adjust the zero adjuster for bringing the pointer to exact zero ohms ontinuity test with analogu 1 Ohm and place your test probes either Vay across a wire and the pointer should show a low reading 28 Now connect the two probes to the points where the short or continuity 15 to be checked as shown in the photo in previous page If the meter shows zero Ohm it means the continuity is present or the connection internally not broken Ideally a good continuity should be
99. x m 4 3 6x 1000 436000 Therefore this R value is 436000Q or 436kQ with tolerance 2 36 Testing Resistor There are two ways of testing resistor using an analogue or digital multimeter Normally if a resistor fails they will either increase in value or open up at all open circuit You can check the resistor resistance by selecting the ohmmeter range in the analogue and digital multimeter If the resistor is in circuit you will generally have to remove the resistor so you are testing only the resistor value and not the other components in the circuit Always be aware of possible back parallel circuit circuits when checking in circuit resistance measurements Testing Resistor With Digital Multimeter I 37 Using Analogue Meter to Test Resistor Adjuster M las 0 25ADl RAT 46m 1225580 gt 2 i OHM or resistance range d gt EE v First you must know the resistor value before you take any measurement With the resistor colour band calculation you have read from the previous section I m sure you have no problem in identifying resistor value by looking at the colour bands Assuming you are measuring a resistor with the colours of yellow purple black and gold from calculation it 1s a 47 Ohms resistor with 5 tolerance Now set your analogue meter to X1 Ohm shorting the probes and calibrate the pointer so that it will stay at zero Ohm Place your meter probes
100. y high speed The only source of X ray in a modern Monitor or TV is from the CRT Prolong exposure to X ray can be harmful However the CRT does not emit measurable X ray if the high voltage is at the high voltage adjustment value only When high voltage is excessive then only X ray is capable of penetrating the shell of the CRT including the lead in glass material Test the brightness and use a high voltage probe to monitor the high voltage each time a Monitor or TV comes in for repair When the brightness is raised usually the high voltage will go down and when brightness 1s reduced the high voltage will go up When troubleshooting a Monitor or TV with excessively high voltage avoid being unnecessarily close to the set Do not operate the Monitor or TV for longer than it is necessary to locate the cause of excessive voltage To ensure continuous X ray protection replace the CRT with one that is of same or equivalent type as the original 8 Wearing Goggles The CRT has a complete vacuum inside It must be handled carefully and safely Always wear goggles to protect the eyes from flying glass in the event of an implosion when removing and old tube from the set and installing a replacement Do not lift the CRT by the neck instead hold the CRT with both hands on the heavy glass front of the tube Also be sure to place the CRT facing downwards on a soft surface 9 Electrostatically Sensitive Devices ESD Integrated circuits IC amp
101. your test probes to pin 1 and 3 Assuming the black probe to pin 3 and the red probe to pin and you don t get any reading then pin is the Collector If you reverse the test probes you will definitely see the pointer kick up In other words we must look for the measurement that don t get any reading and see the red probe connects to which pin If the red probe connects to pin 2 then pin 2 1s the Collector If it connects to pin 1 then pin 1 is the Collector If you reverse the probes you will definitely see a reading In the above case since pin 1s the Collector then pin 3 must be Emitter Although semiconductor data book do show which pin 15 the base collector and emitter we can t fully depend on it as I found it not 100 accurate The best you test and find it on your own 137 Testing Darlington transistor with built in Diode Again we have to depend on semiconductor data book to help us to locate if the particular transistor that you want to test 1s belong to Darlington transistor with or without built in diode TP 120 TIP 121 TIP 122 TIP 125 TIP 126 TIP 127 TIP 130 TIP 131 TIP 132 TIP 135 TIP 1 I Again from the data book we S dw SN Si N Darl4 Li Si N Darl Di Si N Darl Di Si PFJarla Di Si P D HDi Si PR part Di NFfS L DUV DA DOW D gt TIP 120 BOV TIP 120 100V NF S L 60V 5A 65W B 1000 TIP 125 80V TIP 125 100V NE S L 60V BA TOW

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