household appliances with electronics
Contents
1. e Voltage measurement see above TSE N 10 00 AS 22 599 50 85 10 EN 4 Outputs and actuators functional elements The purpose of the control process in the electronics is to provide output signals which guarantee that e first the actuators functional elements of the household appliance do the work re quired at the right time and in the correct manner in order to achieve the result required by the user e second the user is informed about the state of the appliance in a suitable manner and is warned of any malfunction Typical outputs and consumers are e drive motor for washing machine drum circulation or drain pump compressor fan etc e step by step motor e g for water distributor DPS drum positioning system e door lock e magnetron e solenoid valve usually for water inlet but occasionally also in refrigerant circuits e heating element e displays and gauges for functional controls and alarms o electromechanical gauges o indicator lights o acoustical indicators o digital displays LED LC Generally the electronics provides low voltage control signals Signalling and display elements can sometimes be driven directly at this voltage if the absorbed current is also low enough But for actuators of higher power however the supply voltage must be switched via a power supply device Such components are e relays e triacs This is an essential difference to appliances with electromechanical timer2. S z M08 p Ty Inne TBAT Bpo zzi frz a T B081 z 1 Shop egadi nina Edi Circuit diagram of a top loading washer 1 599 50 85 10 EN TSE N 10 00 AS 6 Use of integrated service programmes If the appliances are fitted with integrated service programmes this is more and more the case with the newer appliances these programmes should be your first choice for fault finding A first localization of the fault can be achieved via the displayed fault code This has the advantage of saving yourself time during the fault finding Displaying the fault codes stored in the machines memory should always be the first action checking the configu ration code if applicable the second a wrong configuration code can lead to quite mis leading faults The fault code provides an objective statement about a real diagnosed fault This may be in contrast to the user s assessment which can be subjective The user may also only see a consecutive fault this shall not mean that you can learn a lot about the fault pro cess by asking the user specific questions Additionally the customer service programmes offer the possibility to trigger individual circuits directly which enables you to localize the fault more quickly For some appliances like dishwashers it is possible to run a standardized customer service test programme This is of importance given that the working programmes of th
3. nating voltage It is for this reason that the thyristor is preferably we can say almost ex clusively used for power switching and control Triac symbol Gate If the triac is used to supply the working voltage to the actuator that means not to con trol it the circuit always contains a zero voltage detector This detector makes sure that the trigger pulse will always be generated when the supply voltage sine wave is crossing the zero line TSE N 10 00 AS 24 5995085 10 EN In this way the voltage curve is not distorted from its sinus shape and the effective volt age is not diminished 1 Period 1 thalf wave 2 half wave 4 2 Power control In many cases the activation of the consumers is confined to switching them on or off at the respective suitable time which means that the operating voltage is only supplied In some cases a power control becomes necessary for example of e the heating power e the motor r p m The common procedure for the control of the heating power or of the magnetron power is the periodical switching on and off within a relatively long interval of about 20 40 seconds The power can be controlled via the ratio of ON and OFF time This procedure is well suited for energy controls for conventional heating elements with high thermal inertia It does however already show some disadvantages on microwave appliances although it is widely used there The type of power control that i
4. become part of our daily lives One can not imagine household appliances without them any more But the addition electronic is sometimes used quite loosely The term often appears in connection with simple ap pliances which probably only use one electronic component We want to use the term only when the appliance contains more complex electronic circuits which are essential for its use There are many good reasons for the use of electronic circuits They offer many advan tages in comparison with electromechanical controls e Programme parameters can be controlled more exactly e The functioning of the appliance can be optimised by the use of fuzzy logic e Both lead to a reduced consumption of energy water and chemical products and therefore reduce strain on the environment e Programmes are more flexible and can be adjusted to a new situation The Electrolux group plays the role of a forerunner an update function for example was introduced for the first time ever in an automatic washing machine of the Electrolux Group Here the software of the electronics is updated in order to adjust the appliance to the most modern technical standards as well as to the actual conditions e g new detergents new textiles but also changed washing habits e The user is relieved from having to deal with the operation of the appliance and hav ing to choose and enter individual parameters e g washing temperature spin r p m He merely has to
5. 5 10 EN 1 1 MOTO lt FIELD REVER RELAY SING INTERFERENC SG RELAY SUPPRESSION MICROPROCESSOR m EAC electronics used in AEG automatic washing machines 1998 series TSE N 10 00 AS 599 50 85 10 EN EWM2000 new main electronic board for front loading and top loading washing machines used as a standard part in the whole Electrolux Group TSE N 10 00 AS 8 599 50 85 10 EN 3 Input parameters and sensors 3 1 Typical input parameters Are e switch states binary codes e temperature e level water foam e motor revolutions e degree of residual humidity e water turbidity These input parameters are measured with the help of sensors which make use of the physical dependency of an electrical value from our parameter This is often achieved in several steps e g temperature gt electrical resistance of the sensor gt voltage drop With the concept of the fuzzy logic the programme makes use of additional parame ters which are not measured but estimated via other input parameters or their variation over a certain amount of time In this case the dependency of the two values cannot be exactly defined The connection can be more intuitively felt The amount of crockery in a dish washer for example is determined via the time that is needed for the water to heat up however this time also depends on other factors like the material of the crockery In the following please fi
6. K Electrolux TRAINING PAPER Technical Support Europe HOUSEHOLD APPLIANCES WITH ELECTRONICS FAULT FINDING AEG Hausger te GmbH Publ No AND Muggenhofer StraBe 135 599 50 85 10 DIAGNOSIS D 90429 N rnberg IN EN Germany HOUSEHOLD APPLIANCES Fax 49 0 911 323 1420 WITH ELECTRONICS TSE N Edition 10 00 Contents 1 Why do we use electronic components in household appliances 3 2 General functions of electronics in household appliances 4 3 Input parameters and sensors 9 3 1 Typical input parameters 9 3 2 The most important sensors 10 3 2 1 Switch 10 3 2 2 Thermostat 10 3 2 3 Pressure switch pressostat 11 3 2 4 Flow switch differentisl pressure switch 12 3 2 5 Reed switch 13 3 2 6 Hall generator 14 3 2 7 Temperature dependent resistors 15 3 2 7 1 NTC resistor 15 3 2 7 2 PTC resistor 17 3 2 7 3 Platinum sensor 18 3 2 8 Humidity sensor 18 3 2 9 Tachogenerator 19 3 2 10 Pressure sensor 20 3 2 11 Optical sensor 22 4 Outputs and actuators functional elements 23 4 1 Power supply devices 24 4 1 1 Relay 24 4 1 2 Triac and thyristor 24 4 2 Power control 25 4 2 1 Phase control 26 4 2 2 Pulse width modulation 28 5 Fault finding approach Service manuals and circuit diagrams 30 6 Use of integrated service test programmes 32 7 Measurement possibilities 35 TSE N 10 00 AS o 599 50 85 10 EN 1 Why do we use electronic components in household appli ances Electronic controls of different complexity have
7. e appliance are created in an adaptive way and therefore have no fixed order The cus tomer for example has a complaint that the appliance does not pump the water out after the pre rinse This could be caused by a faulty appliance but it could also be the normal operation because the turbidity sensor did not detect any significant soiling Both cases can only be distinguished with the help of the test programme If the appliance does not have a display which indicates the fault code in clear writing e g C2 the LEDs on the panel can be used to display fault and configuration codes The display has to be done in binary code because an LED has only got two states ON or OFF These are the definitions OFF LED extinguished for 0 ON LED Iit for 1 16 characters can be indicated with a group of 4 LEDs the numbers 0 to 9 as well as the letters A to F these 16 characters are the numbers of the hexadecimal system that is the counting system with the base 16 The following table also displays the signals that can be measured when you suspect that some LEDs are not functioning TSE N 10 00 AS 32 599 50 85 10 EN Please find an overview Decimal number 10 A 11 B 12 C 13 D 14 E 15 F TSE N 10 00 AS Dual number Decimal value LED Signal LED Signal LED Signal LED Signal LED Signal LED Signal LED Signal LED Signal LED Signal LED Signal LED Signal LED Signal LED Sig
8. emperature coefficient i e PTC over its operating range which means that the resistance increases with the resistor heating up operating range is stressed be cause the overall temperature variation is more complicated as shown in the graph be low Its use as a sensor is similar to that of NTC resistors though the latter is more fre quently used in this application a 0 Typical PTC curve 1000000 100000 A E 10000 oO E S 2 1000 k x 100 10 0 100 200 Temperature C TSE N 10 00 AS 17 599 50 85 10 EN 3 2 7 3 Platinum sensors A platinum sensor is a platinum resistor with a constant positive temperature coefficient which means that its increase in resistance is linear We designate it with the chemical symbol Pt and with the value in 2 of the resistance at 0 C Pt500 for example has a resistance of 500 at0 C gt see figure below Other values used are Pt100 Pt1000 RESISTANCE 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 TEMPERATURE C 3 2 8 Humidity sensor This type of sensor is used in tumble driers for the measurement of the degree of resid ual humidity in the washing The drum is connected to the appliance earth back side of the case via a carbon feeler The ribs of the drum are electrically insulated from the rest of the drum and are only connected via a sheet metal strip on the outside of the drum This stri
9. ency of 50 Hz The harmonic cur rents cause harmonic voltages in the electrical supply network which significantly impair not only the power supply but also the other consumers that are connected to it The phase control has its problems at higher power levels because e more recent regulations prescribe tougher limits for harmonic voltages e these regulations must nowadays be complied with otherwise you will not be allowed to bring the appliance on the market in the EU compliance with the regulations is visually indicated by the CE symbol on the appliance e the disturbances caused by harmonic voltages have become more of a problem par ticularly for appliances with electronic controls Voltage spikes and high frequencies can cause disturbances in these circuits if they exceed the immunity levels imposed by regulations If this type of control is used relatively extensive measures for interference suppression are needed TSE N 10 00 AS 26 599 50 85 10 EN Phasenanschnittsteuerung r Phase control using a triac t trigger pulse in first part of half wave gt high RMS voltage gt high power t trigger pulse at peak of half wave gt half RMS voltage gt half power t _ trigger pulse towards end of half wave gt low RMS voltage gt low power TSE N 10 00 AS 21 599 50 85 10 EN 4 2 2 Pulse width modulation PWM This procedure disconnects the motor with a high frequency 16 to 20 kHz from the power su
10. enter his wishes e Improved manufacturing possibilities with consecutively reduced manufacturing costs e Reduced wear and tear due to the absence of moving contacts TSE N 10 00 AS 3 5995085 10 EN 2 General functions of electronics in household appliances Electronic components are mainly used for the following functions e as auser interface Input output electronics which o transfers the user input to the appliance e g the chosen programme the desired temperatures the kind of washing the degree of soiling cooking time etc o again displays the relevant functional parameters like programme steps warning messages for the user s information e asacontrol element the exact programme step is determined as a function of to the user input as well as of the measured functional parameters e g switch positions temperature water level motor r p m etc The output signals are used for o triggering the actuators if necessary via a power electronics o displaying the functional states via the user interface e as a power electronics which ensures the power supply of the actuators ACTUATORS INPUT POWER MOTOR OUTPUT ELEC VALVE USER ELEC TRONICS HEATING TRONICS ETC SENSORS TSE N 10 00 AS 4 599 50 85 10 EN Depending on the complexity and construction of the appliance these functions can be housed on a single or on separated components In the following it is not intended to explai
11. eport two states to the elec tronics yes or no 1 or 0 Quite independent of the value to be measured they only report if a pre defined state has been reached or not In contrast to these the following sensors are used to measure a parameter over the complete relevant measurement range The sensor provides analogue or digital signals which are dependent on the parameter that is to be measured Therefore the possibili ties of the programme layout are increased TSE N 10 00 AS 14 599 50 85 10 EN 3 2 7 Temperature dependent resistors This group of temperature sensors contains NTC and PTC resistors and platinum sen sors The collective term thermistor is also used for these resistors gt Measurement possibilities which apply to all temperature dependent resistors e Resistance measurement the measured value must correspond to the ambient temperature when heated up the value will change exact values can be found in tables or graphs in the service manual e Voltage measurement the voltage can be measured at the sensor contacts or better still at the respective connector on the electronics circuit board The sensor is in a voltage divider circuit Therefore the expected value will be be low the signal voltage With a signal voltage of 5 V we can expect about 2 3 V When heated up the voltage at the NTC will drop whereas it will increase at the PTC 3 2 7 1 NTC resistor The NTC resistor belongs to the gro
12. he voltage is existent the defect must be somewhere in the component itself l no voltage can be measured you need to follow the connection cables and measure the voltage at more suitable positions Testing in this way damage to cables or contacts can be identified and the fault can be further localized Note using the service manual and circuit diagram make sure that the missing voltage is not a result of the triggering of a safety function With the help of a suitable measurement instrument e g snap on ammeter the current can be measured as well The measurement of working currents with the help of a multimeter is usually not practicable TSE N 10 00 AS 35 599 50 85 10 EN 3 Signal voltages at inputs and outputs of the electronics as well as at sensors At temperature dependent resistors you can expect values that are roughly half of that of the signal voltage when heated up the voltage must change its value in the same direction as the resistance At all types of switches reed switch pressure switch thermostat flow switch etc voltage zero for closed switch signal or operating voltage for open switch If poosible induce change of the switching state in order to measure both states Tachogenerator a voltage of a few volts can be generated by turning the gen erator by hand 4 Functional parameters Temperatures o For cooking appliances oven temperature o For cooling and freezing appliances primar
13. ily temperatures inside additionally temperatures at the refrigerant circuit For measurements in the inside atten tion needs to be paid that not the air temperature but the average storage temperature is measured gt e g in a glass of water that has already been in the fridge for about 30 minutes o For different appliances switching temperatures of thermostats Time programme steps with reference to the service manual it needs to be de termined and measured if the programme steps take place in the prescribed or der and at the prescribed time Choose a customer service test programme if possible because other programmes are variable in their order 5 Resistances particularly of components heating elements motor coils coils of solenoid valves it needs to be measured that the resistance corresponds to the prescribed value Generally this value can be found in the service manual Even if you do not know the exact value the measurement can provide important clues o avery small value indicates a short circuit o avery high value indicates an interruption sensors o for temperature dependent resistors NTC PTC Pt tables or graphs can generally be found in the manual In any case the resistance must show the change that is expected when it is heated up for example by your hand a de crease for NTC an increase for PTC or Pt Alternatively temperature dependent resistors can be simulated with the help of a resisto
14. ing But as this sensor is a standard component frequently used check by exchange though generally not advisable is a usable method 3 2 11 Optical sensors This sensor for example is used in dishwashers as a turbidity sensor In a component through which water is flowing an LED and a photodiode are posi tioned opposite each other When the water is turbid the light that is emitted by the LED is dimmed when it reaches the photodiode The output voltage of the photodiode is reduced proportionally On the basis of this voltage the electronics estimates the degree of soiling of the crockery or the residue of detergent respectively With the help of this information it is able to decide on the following programme required to obtain a satis factory rinsing result It is important to note that the output voltage would slowly decrease over time due to deposits at the sensor walls In order to prevent this the sensor that is used in Electrolux dishwashers is calibrated at the end of each cycle during the last rinsing run The input voltage is slowly increased during this process this is possible in the range from 6 to 11 4 V The result is that the output voltage in this progamme step is at a constant 4 3 V This value signals to the electronics that the water is clear Note if the sensor is calibrated in the air which is the case during the service checks the output voltage must be at 3 5 V gt Measurement possibilities
15. ition by a permanent magnet if the door of the drum is in its top position a ferromagnetic strip that is fixed to the pulley affects the magnetic field and the reed switch opens It provides the gauge input signal for the electronics and helps to position the drum via the motor control e Door switch in cooling appliances the magnet is in the door and the reed switch is in the door frame gt Measurement possibilities e Like switch 3 2 1 can be triggered with an external magnet TSE N 10 00 AS 13 599 50 85 10 EN 3 2 6 Hall generator A Hall generator is an electronic signal generator which amplifies the so called Hall voltage The Hall voltage is generated by magnetic fields The Hall generator can be used to prove the existence of these magnetic fields and to measure them The application in household appliances is relatively simple it is for example used in dish washers to recognize the rotation of the upper rotary arm The magnetic field is generated by a permanent magnet in the flushing arm The Hall generator is located in the door When the arm passes by the door the output voltage is at 4 5 V otherwise at 0 1 V This application of the Hall generator is similar to that of a reed switch gt Measuring possibilities e Signal voltage values are indicated above All switches listed up to this point as well as the Hall generator in this application can be categorized under binary sensors All of them simply r
16. n the processes that take place inside an elec tronics In general there are no accessible measuring points Details with regard to this fall in the domain of specialized suppliers and will not be found in the service documen tation of the appliance For us the electronic circuit will remain a single spare part and is treated like a black box In no case will individual components on a board be exchanged This is also not allowed for reasons of safety The implementation of unsuitable components could cause for example fires We want to investigate what happens around the electronics and measure inputs and outputs if that is possible as well as the functioning of the components which commu nicate with the electronics With the help of these techniques faults can be isolated more closely so that only those parts are exchanged which are really necessary TSE N 10 00 AS 5995085 10 EN Examples IIND NE 10 11 12 13 1 3O BETA Jaia IO mo lojto OD it me Gj o G Ol GM al 5 m 9 EE 40 Main circuit board Programme selector User interface Analogue pressure sensor Safety pressure switch Temperature sensor Motor Heating element Water inlet valve Door lock Circulation pump Drain pump Drum self positioning DSP sensor Main electronics of a top loading washing machine with connections to sensors and functional elements TSE N 10 00 AS 6 599 50 8
17. nal LED Signal LED Signal LED Signal 2 933 5995085 10 EN The powers of two 8 4 2 and 1 are assigned to the LEDs You get the displayed character by adding up the numbers that are assigned to the lit LEDs As an example 8 4 2 1 8 4 4 13 or the letter D A 10 B 11 F 15 The two digit code can be displayed with two groups of 4 e g C2 8 4 2 1 8 4 1 2 The error codes and the arrangement of the LED groups are described in the respective service manuals Errors in reading the code can be avoided easily Use a template that shows the num bers 8 4 2 1 right next to the respective LEDs or an adhesive tape The identical display is used to read and to set the configuration code The hardware of the electronics circuit boards for washing machines are identical for a complete series They must be programmed for the special features of the individual model with the help of this code The programming must be done during the exchange of the board and it is of crucial importance to avoid any errors during this process TSE N 10 00 AS 34 599 50 85 10 EN 7 Measurement possibilities In the following listing of measurement possibilities we do not want to investigate in fur ther detail the possibilities that you have in a workshop or laboratory and when using special measurement and display instruments We want to co
18. nd some examples for such values e amount of washing via the absorbing behaviour of the washing which really means via the time gradient of the water level e amount of crockery via the heating up speed meaning via the water temperature e soiling via the water turbidity e Unbalance via fluctuation of motor r p m TSE N 10 00 AS 9 599 50 85 10 EN 3 2 The most important sensors 3 2 1 Switches Switches are the most frequently used sensors System states are reported to the elec tronics via switches The switches are e set by the user either o directly e g I O switches various selector switches or o indirectly e g door switches e or they are activated by the system during the programme gt Measuring possibilities e Resistance measurement continuity this tyoe of measurement provides a way to find out if the switch is in its expected switching state open or closed e Voltage measurement is another way to detect the switching state voltage is present with the switch in its open state 3 2 2 Thermostat A thermostat is an electromechanical temperature switch that opens or closes an electri cal circuit at a certain temperature The switching temperature is e either set mechanically gt temperature control or e set to a fix value gt temperature limiter is generally used as a safety element According to their construction we can distinguish between e bimetal thermostat e metal r
19. nfine ourselves to the measurements that can be performed quickly at the location with a common multimeter This one measurement instrument should always be taken by the customer service engineer and made use of regularly The following values can be measured functional parameters electrical values of components using the multimeter when the appliance is connected to the power supply voltages maybe currents when the appliance is separated from the power supply resistances It is necessary to mention that not all of these possibilities are always available without restrictions In some countries like Great Britain it is strictly prohibited to measure at an open appliance that is connected to the power supply Even when there are no regula tions that restrict the measurements they must always be performed in a manner which guarantees the absolute safety of the customer service engineer and that of the envi ronment What can be measured 1 Power supply of the appliance that means Does the voltage at the connection of the appliance have the correct value Is the appliance connected in a correct manner Is there any voltage at the connection point inside the appliance 2 Voltage supply to the components after the potentially faulty component has been identified choose an operational state in which a power should be supplied to the component Now the voltage can be measured at the terminals of this component If t
20. od expansion thermostat e liquid expansion thermostat e vapour condensation thermostat used in refrigeration gt Measurement possibilities e like switch 3 2 1 Please refer to the switcing temperatures in the service manuals in order to determine the expected switching state TSE N 10 00 AS 10 5995085 10 EN 3 2 3 Pressure switch pressostat A pressure switch consists of a manometric cell with a membrane fixed on the inside The membrane deforms under the influence of the pressure and activates mechanically one or several switching contacts at pre set pressure values Pressure switches are generally used as level switches The manometric cell is con nected to the tub of the washing machine or the dishwasher via a hose The rising of the water column causes the air pressure in the hose to rise water level low pressure low contact open water level reaches pre set value pressure rises contact close 1 manometric cell 2 membrane 3 switching contacts gt Measurement possibilities e Like switch 3 2 1 TSE N 10 00 AS 11 599 50 85 10 EN 3 2 4 Flow switch differential pressure switch There is a physical law that can be used to detect the existence of the flow like for ex ample the flowing of water through a pipe It is Bernoulli s law that says that the sum of flow pressure and static pressure in a flow always remains constant If the flow is directed through a contracted cross section Venturi n
21. ozzle the local flow speed and therefore the flow pressure as well will rise The static pressure decreases and is less than the pressure upstream of the nozzle When both pressures are directed into a differential pressure cell via thin tubes the resulting deformation of the membrane will trigger a switching process If the flow is non existent the pressures upstream of and in the Venturi tube are equal and the differential pressure switch will open again If water is heated with the help of a flow heater the heating element must be switched via a flow switch in order to avoid heating when there is no flow no water flow pressures equal contact open 1 differential pressure cell 2 membrane 3 needle 4 Venturi nozzle 5 switching contact TSE N 10 00 AS 12 599 50 85 10 EN water flow existent static pressure in nozzle lower than upstream contact closes gt Measurement possibilities e Like switch 3 2 1 3 2 5 Reed switch Reeds made from ferromagnetic material are used as switching contacts for this type of switch The switching process is triggered by a magnetic field Typical examples for applications e Salt or detergent level gauge for dishwashers in the container there is a floater with a permanent magnet which in the desired position activates a reed switch outside the container e DSP drum positioning aid for top loaders the reed switch of the sensor is kept in its normal closed pos
22. p is scanned by a metal brush The brush and earth of the device are therefore only electrically connected via the moist washing The dryer the washing becomes the more the electrical resistance of the washing increases The drying process is controlled via the measurement of this resistance gt Measurement possibilities A change of the resistance cannot be detected without any moist washing How ever contact problems are a frequent cause for malfunction Therefore the fol lowing resistances can be measured as well TSE N 10 00 AS 18 599 50 85 10 EN e Contact resistance between the ribs of the drum and the input from the scan ning brush on the electronic circuit board e Contact resistance between drum and case e Insulating resistance between ribs and drum 3 2 9 Tachogenerator This generator is used to measure the motor r p m The tachogenerator is firmly con nected to the motor shaft In a coil that rotates in a magnetic field a voltage is gener ated which is proportional to the revolutions The generator can be constructed as e DC tachogenerator that takes the voltage from a commutator e AC tachogenerator this type is nowadays more frequently used because of its sim pler construction it does not need any commutator and the layout can be inverted i e rotating permanent magnet and fixed coil For this type the frequency of the al ternating voltage is also proportional to the r p m In the digital circuits u
23. pond to questions or complaints TSE N 10 00 AS 37 599 50 85 10 EN
24. pply The relation of switching on and off time can be varied via the microproc essor The name PWM pulse width modulation stems from the fact that the width of the individual impulses changes Due to this principle the motor speed can be controlled over a very wide range More important the high pulse frequency leads to short reaction times which allows the use of very high spin speeds of up to 1800 r p m When using this type of control the motor is fed with pulsating direct current 1 High pulse width D Low pulse width TSE N 10 00 AS 28 599 50 85 10 EN Power supply Code for direction of drum Amovement and and for field tapping Motor electronics Control electronics Signal transmission between control electronics EWM3000 und motor electronics for automatic washing machines using pulse width modulation TSE N 10 00 AS 29 599 50 85 10 EN 5 Fault finding approach service manuals and circuit diagrams We would like to point out how important it is to approach fault finding systematically and logically It is of major importance to use the product documentation that means the service manuals and the circuit diagrams e Please do always identify the appliance unmistakably when you take the order PNC E Nro and also Series No F No if possible Service manuals can be pre pared and taken with you This has always been desirable but is of crucial impor tance for appliances with integrated diagnosis
25. programmes because these pro grammes can only be used and interpreted correctly with the help of the documenta tion The basics of fault finding for conventional appliances remain mainly valid e At first please test if there is a fault at all In many cases the appliance works ac cording to its specifications but the customer has got other expectations in mind they may be justified or not This is often the case with cooling and freezing appli ances Always try to convince the customer with arguments and to refer him to cus tomer services if necessary Never exchange parts or even the whole appliance This only leads to costs without solving the problem e lf there is a fault localize the faulty circuit o via the fault code if available o if the code is not available use the symptoms of the fault and check on the wiring diagram what might cause such symptoms e do not just exchange components in this circuit but check the complete path of the current with reference to the circuit diagram by measuring see section 6 e search for commonplace faults first o correct connection o contacts a very frequent cause for faults pay special attention to plug connec tions of electronics you may need to physically move them o hose connections possibly blocked hoses e activate components directly if service programmes allow this TSE N 10 00 AS 30 599 50 85 10 EN aummubn 00 F9O l OF seo D818 SH wee oe
26. r decade o For switches 0 or a very lowl value for a closed switch or a very high value for an open switch If possible induce a change of the switching state in order to measure both states TSE N 10 00 AS 36 599 50 85 10 EN Wiring and contacts o must be checked for a small resistance Move the contacts in order to find out if the value changes or not For all measurements of resistances you should measure the complete wiring if possi ble However this may depend on the accessibility Remove for example the plug from the electronics and measure from there If the values are within the normal range you have checked the wiring as well as the component in one single measurement Only if the measurement values are different from the prescribed values you have to continue to approach the component itself At this point it is also important to note that there are no simple measurement possibili ties for some components In some cases the checking by exchanging is recommend able e g for the analogue pressure sensor If you choose this method of testing please note the following if you find that the component was not faulty after all please put the old part back into its former place Please remember it does not take much time to keep a record of the measurement results and the measurement conditions Such records can be of great help if the case develops into something much more complicated later on or if you need to res
27. s In these units the complete working current runs via timer contacts Note triacs or relays are often positioned on the main board so the line voltage can be measured at the outputs This is however not the working voltage of the electronics TSE N 10 00 AS 23 599 50 85 10 EN 4 1 Power supply devices 4 11 Relays A relay is an electromechanical power supply device The control voltage is connected to the relay coil often via a triac because the coil absorbs a relatively high current An electromagnet closes the relay contact s The working current of a consumer motor heating element etc is directed via these contacts Relays are used to supply consumers of higher power but also if safety standards re quire switching to be done by actual contact opening Both conditions apply mainly to heating elements 4 1 2 Triac and thyristor Both components are semiconductor elements and belong to the group of the controlla ble diodes A controllable diode is triggered by a current pulse at the gate This means that it is brought into a conducting state The triggering point can be moved within a half wave with the help of an adjustable resistor The thyristor is only controllable in one current direction and provides therefore a pul sating current The triac is basically comparable with two thyristors that are switched in an antiparallel way It is controllable in both current directions and uses both half waves of the alter
28. s most important to us is that for the main drive motor of automatic washing machines The speed of this drive motor must cover a very wide TSE N 10 00 AS 25 599 50 85 10 EN range from maybe 25 r p m in the wool or hand wash programme to the maximum spin r p m of 1800 The speed range can be chosen by adding or removing field coils For a continuous and fast reacting control within a range we can use e phase control e pulse width modulation Basically the two procedures are no different from the clocking which was mentioned before Only the clocking interval is shortened considerably to a half period of the sup ply frequency i e 10 ms for phase control and to 50 60 us for pulse width modula tion 4 2 1 Phase control This procedure cuts off parts of the symmetrical sinus curve with the help of electronic components like a triac As mentioned in 4 1 2 a control circuit can supply a trigger pulse at the triac s gate either at zero crossing i e at 0 phase angle or at any phase angle between 0 and 180 Increase of the phase angle at which the trigger pulse occurs will lead to a reduction of the effective RMS voltage and hence to a progressive power reduction The major disadvantage of the phase control is that the current curve deviates significantly from its original sinus shape This means that harmonics i e oscillations with frequencies that are multiples of 50 Hz interfere with the supply frequ
29. sed on most control electronics the frequency measurement is more convenient and more exact than the measurement via the voltage gt Measurement possibilities e Asmall voltage can already be measured while turning it by hand e The resistance of the coil can be measured TSE N 10 00 AS 19 599 50 85 10 EN 3 2 10 Pressure sensor The sensor is connected in the same way as the electromechanical pressure switch In contrast to the latter not only switching processes at pre defined pressure values are triggered but the pressure and thereby the level is measured continuously Air intake Membrane Coil Oscillator electronics Magnetic ring Spring Adjusting screw Connection plug Contact 1 Out Contact 2 GND Contact 3 5V DC ONOOaRWD The magnetic ring is lifted due to an increase of the air pressure in the hose As a result the magnetic features are changed This in turn causes a decrease of the oscillator fre quency TSE N 10 00 AS 20 5995085 10 EN 5V 3 DIGIT 1 0 V 2 FREQUENCY IHE 15 Iw c00 x 304 PRESSIHE imi Heb TSE N 10 00 AS 21 599 50 85 10 EN gt Measurement possibilities e It is not possible to measure the frequency using a simple multimeter Even with multimeters having this possibility interferencve with the line frequency makes the measurement difficult e The existence of an output voltage may be a first indication that the compo nent is work
30. up of semiconductors generally a mixture of differ ent metal oxides It has a very high resistance at low temperatures When the tem perature increases more electrons are released from their bonds As a result the electri cal resistance decreases The resistor therefore has a negative temperature coefficient abbreviated NTC This is the switching symbol used TSE N 10 00 AS 15 599 50 85 10 EN A typical curve looks like this RESISTANCE Q 30 25 20 i ee 23 22 2202 E E ine ee eee TO 2 6 te an le en ES la u A ne 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100 TEMPERATURE C In order to use an NTC sensor for temperature control a bridge circuit like the simplified one shown below can be used A controllable resistor Rr is set to the value of the NTC sensor at the desired temperature This can be done via the temperature selector or via the programme electronics As long as the two resistances are not equal the voltage U is generated This voltage can be used for the control of the heating element As soon as the set temperature is reached U becomes 0 m If we want to actaully measure the temperature for an indicating gauge for example we can do this by measuring the voltage drop TSE N 10 00 AS 16 599 50 85 10 EN 3 2 7 2 PTC resistors This resistor is also a semiconductor component In contrast to the NTC resistor it has a positive t
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