SERVICE MANUAL
Contents
1. AC INPUT VERTICAL MODE CONTROL CIRCUIT IC5801 CONTROL CIRCUIT VR801 VR806 VR803 VR807 VR804 VR808 VR805 SW801 LINE FILTER L101 C103 C101 C104 C102 VIDEO OUTPUT AMP R G gt R 0902 B G 0901 0903 AUTO BIAS CIRCUIT 10952 0952 0950 0953 0951 VIDEO CIRCUIT G2 CONTROL CIRCUIT 0904 R933 R931 R936 HORIZONTAL amp VERTICAL 05 IC301 VERTICAL OUT PUT CIRCUIT 16302 HORIZONTAL DRIVE CIRCUIT Q402 T402 HORIZONTAL OUT PUT CIRCUIT 0401 T401 DEFLECTION CIRCUIT SWITCHING AMP 101 0191 SUPPLY SWITCHING TRANS v DY HDY 72 HIGH VOLTAGE DC OUT PUT VOLTAGE 242. SERVICE MANUAL 1748 1948 fcOr f e f lt isplay Solution Kortek Corporation KORTEK Corporation KT XX48 1 PRECAUTIONS 1 1 SAFETY PRECAUTIONS WARNINGS Service should not be attempted by anyone unfamiliar with the necessary precautions on this monitor The following precautions are necessary during servicing 1 For continued safety do not attempt to modify the circuit board 2 Disconnect the AC Power before servicing 3 When the Monitor is operating do not touch any heat sink on the Chassis as it is self heated 1 1 1 FIRE amp SHOCK HARZARD 1 During servicing pay attention to the original wires whether it is uncoated or undressed especially the wires in the high voltage circuit section If there is any uncoated or melted wire is found then please do not try to replace the related parts and wait for the qualified service person s coming 2 Many electrical mechanical parts in this monitor have special safety related characteristics for protection against shock hazard and others These characteristics are often passed unnoticed by a visual inspection and the protection afforded by them cannot necessarily be obtained by using replacement components rated for higher voltage wattage etc Replacement parts which have these special characteristics are identified in the manual and supplements by shading on the schematic diagram and the parts list 3 When replacing Chassis always be certain that
3. WN D 114148 seak WA 1 4 2 8 h PULSE gt TS woo 1 2 A seak VV 1 2 x 81 js 1 1 1 VW BLANK PULSE A PULSE GENERATOR CIRCUIT supplies power to the control of AUTO BIAS circuit and produces and supplies pulse only while blanking period to prevent error For more detailed TIMING CHART please refer to the waveform of the circuit diagram The description of the circuit is as follows HORIZONTAL amp VERTICAL BLANK PULSE is supplied through R917 adjusts the waveform delay and width to ease AUTO BIAS movement at PULSE OSCILLATOR circuit composed of IC902 C920 R921 R923 R924 R922 output to PIN 7 of IC902 Since the output waveform can not have enough current the waveform is output to PIN1 after amplifying the current using OP AMP and supplies the current to AUTO BIAS CONTROL CIRCUIT KORTEK Corporation KT XX48 3 MAIN PCB Circuit Description 1 POWER SUPPLY POWER SUPPLY SYNC PULSE INPUT MANUAL DEGAUSSING Power supply is composed line filter switching amp and switching trans circuit line filter circuit eliminates the noise of the power line supplied from
4. all the protective devices are installed properly 4 leakage current check figurel 1 KORTEK Corporation KT XX48 READING SHOULD NOT BE ABOVE 0 45mA UNDER TEST TEST ALL EXPOSED METAL SURFACES LEAKAGE CURRENT TESTER ALSO TEST WITH PLUG REVERSED USING AC ADAPTER PLUG AS BARTS REQUIRED GROUND Fi gurel 1 TEST METHODE 1 1 2 X RADIATION WARNING The only potential source of x radiation is the picture tube however when the high voltage Circuitry is operating properly there is no possibility of an x radiation problem The basic precaution is to keep the high voltage at the factory recommended level 1 To measure the high voltage use a high impedance high voltage meter to chassis and to the CRT anode 2 Turn the contrast control max clockwise 3 Measure the high voltage The high voltage meter should indicate the following factory recommended level 4 If the actual level exceeds the max factory set level then immediate service is required to prevent the possibility of premature failure of components 5 To prevent X RADIATION possibility it is essential to use the specified picture tube 6 The nominal high voltage is 24KV and not exceed 27KV at zero beam current at rated voltage KORTEK Corporation KT XX48 1 2 SERVICING PRECAUTION WARNING 1 First reading safety precaution section of this manual If unforeseen circumstances create conflict between the
5. circuits PIN9 of T101 is the circuit supplying voltage to VIDEO OUT PUT AMP through 110V line and the circuit is composed of D121 C123 L111 and C124 PIN10 is the circuit supplying B to VERTICAL OUT PUT AMP with 40V line and is composed of D122 and C125 PIN11 is the circuit supplying activation voltage to HORIZONTAL VERTICAL OSC IC with 12V line and is composed of D123 C126 L112 C127 and C132 12 is supplying voltage to CRT heater through 6 3V line and the circuit is composed of D124 C128 L113 R116 and C129 As other circuits for power supply auto and manual degaussing circuits are composed of PH101 and RL101 KORTEK Corporation KT XX48 2 HORIZONTAL amp VERTICAL MODE CONTROL CIRCUIT HORIZONTAL amp VERTICAL MODE CONTROL H POSI CONTROL CONTROL PINCUSHION 657 CONTROL CONTROL IC601 is in charge of horizontal amp vertical sync and mode control checks H V SYNC input through PIN3 4 then output through PIN5 6 and regardless of input SYNC output SYNC is always output negative value PIN1 2 forms oscillator circuit of IC601 and is composed of C601 C602 X601 and R603 PIN15 PIN23 output low signal from corresponding mode after checking the status of input H V SYNC Here the output low signal and inverted high signal from Q603 control horizontal position horizontal size vertical size pincushion etc PIN24 use
6. outside prevents the noise occurred from switching amp from flowing out through outer power line and the circuit is composed of C101 L101 C102 C103 and C104 The AC power supplied through line filter is then supplied to D101 and transformed into ripple current and finally transformed into DC by C105 The circuit of switching amp is composed of IC101 Q101 and peripheral circuits IC101 oscillates and controls and Q101 performs switching function IC101 starts oscillation by the transformed DC power supplies through R102 and outputs the pulse to PIN6 IC101 PIN3 R106 R115 and R108 are composed to form OVER LODE prevention circuit and IC101 PIN1 2 and the peripheral circuits 102 performs voltage adjustment and 13 KORTEK Corporation KT XX48 stabilization function T102 is SYNC TRANS used to match the frequency of the monitor and power supply and used to prevent noise on the screen when the distance between switching trans and deflection yoke is close Switching trans transforms the produced pulse to fit to the voltage of each part and supplies the pulse to these parts DC voltage is supplied to PIN2 of T101 the pulse is produced at and PIN6 7 is composed of a circuit which feeds back the changed amount of voltage and supplies VCC of IC101 PIN15 is a circuit supplying horizontal deflected voltage through 49V LINE and is composed of D120 C120 L110 and C121 R120 and C131 are improved FCC and SMOKE NOISE
7. 402 generates pulse from switching Q402 The generated pulse is exposed to PIN4 1 of T402 and is supplied tohorizontal output TR R401 is resistor for current regulation and C417 performs noise filter function 406 is the circuit for input current restraint and noise elimination 5 HORIZONTAL amp VERTICAL OSC HORIZONTAL amp VERTICAL OSC CONTROL H POSI CONTROL S PIN CONTROL V BLN CONTROL V SIZE CONTROL V POSI CONTROL tt M222 w 39K F 7K M473 AAA 115 HPLLT 2 Ah 4 veos 39K HSYNC SIZE CONTROL 6 2K F 1 4 2N3906 221pF 5208 z gt 1 5 1 2W 47 1 1 N CONTROL PULSE 301 TDA4858 is in charge of horizontal 4 vertical OSC drive and is activated by 12V of PIN9 Vertical oscillator is composed of PIN22 23 24 C306 R306 and C305 PIN28 controls V BLN PIN18 V SIZE PIN17 V POSI Vertical drive output is performed by PIN12 and 13 PIN14 and PIN15 are V H SYNC input terminals and are always supplied in negative value Horizontal oscillator is composed of PIN27 28 29 C302 R303 and R304 C303 R305 and C304 connected to PIN26 perform AFC function PIN2 of IC301 performs X RAY CONTRO
8. 6 G OUTPUT OUTPUT 10UF 50V CONTRAST 7 CONTROL 59 12V 1 QUF 25V E G E B 12V Video signal 0 7V PP supplied from CN901 PIN2 BLUE 4 GREEN 6 RED is supplied to IC901 PIN4 6 8 via C902 C903 C905 IC901 performs VIDEO PRE AMP function the amplitude is determined by DCBIAS of PIN 1 2 3 and OUT PUT VIDEO LEVEL is determined by PIN9 CONTRAST DCBIAS and contrast controlled VIDEO SIGNAL are output to PIN 19 RED PIN 17 GREEN PIN 13 BLUE and supplied to VIDEO OUT PUT CIRCUIT KORTEK Corporation KT XX48 For detailed information please refer to KA2141 DATE BOOK 2 VIDEO OUT PUT AMP VIDEO OUTPUT AMP CRT K B s 5 The SIGNAL supplied by VIDEO PRE AMP is input to the base of Q903 The amplitude of Q903 is determined by EMITTER RESISTOR R938 and COLLECTOR RESISTOR R937 R945 and L903 C935 circuits are composed for frequency loss prevention and compensation VIDEO OUT PUT AMP is composed o 3 circuits R G B the explanation aboveis about RED and since LOCATION NO for the components are applied differently please refer to complete circuit for GREEN and BLUE circuits For A S or value changes for the components please understand the characteristics of the components thoroughly and apply appropriately R938 and R937 are for 1 temperature compensati
9. CORNERS 0 35 mm VERTICAL HIGH LEVEL 3 0 5 0 VOLT LOW LEVEL 0 0 0 0 1 VOLT NON LINEARITY 5 HORIZONTAL SYNC POLARITY POSITIVE NON LINEARITY X 281 0 020 y 311 0 020 LUMINANCE ADJUSTABLE WITH USER CONTROL 10 3 F L 55 5 F L WHITE BALANCE 21 KORTEK Corporation KT XX48 5 IROUBLE SHOOTING GUIDE KORTEK Corporation KT XX48 TROUBLESHOOTING CHARTS NO RASTER OR HIGH VOLTAGE ___ Ri 1492 NO 1401 54v NO CHARACTER OR PICTURE 2905 AUTO BIAS FAIL G1 PULSE R917 YES NO 9924 YES t NO SUB PCB YES 24 R936 R931 Na G2 R933 R934 570V 0953 950 NO 0908 0910 0950 0952 0909 56992 905 NO 61 50904 C921 R926 TROUBLE IN HORIZONTAL OR VERTICAL SYNC NO POWER 1 2 6 BLOCK DIAGRAM 23 KORTEK Corporation KT XX48 PRE AMP KT XX48 BLOCK DIAGRAM 901 CONTRAST CONTROL PULSE GENERATOR IC902 HORIZONTAL amp
10. L function and the circuit is composed of F B T PULSE D301 C311 R313 R312 and C307 PIN5 and its peripheral circuits detect and compare F B T PULSE and output the pulse to PIN6 for constant high voltage at anytime VR301 is high voltage control VR and 17 KORTEK Corporation KT XX48 since its high voltage is adjusted to 24 5KV at the manufacturing process there is no need to adjust when performing A S PIN11 of IC301 and its peripheral circuits control H SIZE The voltage proportional to the changing value of DC voltage and high voltage of PIN32 is output to PIN11 and controls Q408 and Q410 to control H SIZE Moreover S PIN and V BLN are composed at PIN11 and is adjusted by Q408 and Q410 6 HORIZONTAL OUT PUT CIRCUIT HORIZONTAL OUTPUT CIRCUIT T401 KFS 61 687 1 C5584 HORIZONTAL DRIVE gt S o DD84 INPUT 22 1 4W 505 400605 gt 15 25 IRFS640A 22 PULSE M104 INPUT g 22K HORIZONTAL OUT PUT CIRCUIT is composed of OUT PUT Q401 FLY BACK TRANSFORMER 7401 0403 VR401 0411 0412 which are RASTER POSITION ADJUST CIRCUIT T501 and its peripheral circuits connected to PIN14 of T401 are forming DYNAMIC FOCUS circuit HORIZONTAL DRIVE PULSE is supplied to the base of Q401 and pulse is generated at resonant circuit which is composed of T401 HO
11. RIZONTAL DEFLECTION YOKE C401 and C402 PIN2 of T401 is supplied with controlled voltage from Q403 The voltage is supplied in varied values depending on the frequency It is as follows 31 5KHz 54V 38KHz 65V 48 2 85V Pulse of 800 900V value is generated at PIN1 of T401 and the high voltage is supplied to the anode of CRT after boosting the value to 24 5KV Moreover T401 supplies FOCUS SCREEN voltage to CRT VR401 is horizontal raster position control VR and is supplied 10V from T401 0PIN3 10V PIN4 respectively and 18 KORTEK Corporation KT XX48 change DC voltage to Q411 and Q412 to move the horizontal raster to the left or right 7 VERTICAL OUT PUT CIRCUIT VERTICAL OUTPUT CIRCUIT 12V 40V VDRVE1 TDA4866 154 2 DEFLECTION VERTICAL COIL o o JUMP M 2 2WF w 174W 5 6K F IC302 TDA4866 is VERTICAL OUT OUTPUT CIRCUIT It is the circuit which generates sawtooth wave form needed for deflection and supply to deflection yoke The waveform supplied to DRIVE 1 2 is boosted and output to PIN6 12V is supplied to PIN3 of IC302 and 40V is supplied to PIN7 R334 and R335 are 1 F grade FEED BACK resistors used for circuit accuracy and temperature compensation 19 KORTEK Corporation 4 SPECIFICATIONS Model KT 1748 PARAMETER MIN TYP MAX UNITS OPERATING VOLTAGE 90 115 230 260 VAC OPERATING POWER 60 80 WATTS LEAKAGE CURREN
12. T TO CHASSIS GND AT 250VAC 50 60HZ lt 0 40 0 45 mA LINE NEUT IN COMMON LEAKAGE CURRENT TO CHASSIS GND AT 250VAC 50 60HZ lt 2 0 2 4 mA LINE NEUT INCOMMON IMPLOSION PROTECTION MAGNETIC SHIELD DEGAUSSING PROVIDEO BY BAND AND MOUNTING LUGS INTERNAL MANUAL AUTO VIDEO SIGNAL RASTER DIM ADJUST RANGE VERTICAL RASTER DIM ADJUST RANGE HORIZONTAL 0 7Vpp 75 OHM MONITOR TERMINATIONS HOLD IN RANGE MODE 640 0 480 8000 600 1024 768 VERTICAL SCAN RATE 45 90 HZ HOLD IN RANGE HZ HORIZONTAL SYNC POLARITY HIGH LEVEL LOW LEVEL NON LINEARITY WHITE BALANCE LUMINANCE POSITIVE 3 0 5 0 VOLT 0 0 0 0 VOLT 2 10 i ee X 281 0 020 y 311 0 020 ADJUSTABLE WITH USER CONTROL 10 3 F L 55 5 F L 20 KORTEK Corporation KT XX48 Model KT 1948 PARAMETER MIN TYP MAX UNITS OPERATING VOLTAGE 90 115 230 260 VAC OPERATING POWER LEAKAGE CURRENT CHASSIS GND AT 250VAC 50 60HZ 040 0 45 mA LINE NEUT IN COMMON LEAKAGE CURRENT TO CHASSIS GND AT 250VAC 50 60HZ lt 2 0 2 4 mA LINE NEUT IN COMMON OPERATING TEMPERATURE 10 60 REL HUMIDITY OPERATING 10 90 IMPLOSION PROTECTION PROVIDEO BY BAND AND MOUNTING LUGS MAGNETIC SHIELD INTERNAL DEGAUSSING MANUAL AUTO VIDEO SIGNAL 0 7Vpp 75 OHM MONITOR TERMINATIONS RASTER DIM ADJUST RANGE VERTICAL RASTER DIM ADJUST RANGE HORIZONTAL MODE PINCUSHION
13. on and R945 is for 5 grade temperature compensation for TR Q903 and NPO type capacitor must be used for C935 3 G2 CONTROL CIRCUIT G2 CONTROL CIRCUIT AA Q 92 5042 AV kz 102PF 2KV G2 CONTROL CIRCUIT is used to omplement the movement of AUTO BIAS circuit and there is no need to adjust SCREEN voltage even when replacing CRT The circuit works as follows When R G B CATHODE voltage of CRT detected through R936 R931 R933 is applied to the base of Q904 Q904 automatically controls screen voltage and maintains the luminosity of the 10 KORTEK Corporation KT XX48 screen 4 AUTO BIAS CIRCUIT AUTO BIAS CIRCUIT AUTO BIAS CIRCUIT is the circuit which detects the space between the cathodof CRT and GRID 1 and automatically adjusts BIASvoltage It compensates the color changes when warming up and maintains evenly Further it extends the life time by compensating the emission loss when CRT isused for long time and CRT can be replaced without additional adjustment when A S The description of circuits is as follows PIN4 of SUB PCB is connected with the cathode of CRT CRT CATHODE is composed o 3 electrodes R G B and GRID1 is also composed electrodes electrodes maintain spaces different from each other and BIAS voltage should supply voltages proportional to these spaces to acquire e
14. s 5V for the activation voltage 12601 20603 R607 in charge this function AR601 performs pull up resistor function PIN15 PIN22 of C601 and supplies 5V to each gate 15 KORTEK Corporation KT XX48 3 CONTROL CIRCUIT CONTROL CIRCUIT We 4 7K N 4 7K N TANTAL 50KB 47K 1 uF 16V Oh 10K 1 2W V POSI 50KB JUMP y size 5 kB 47K NW MANUAL DEGAUSSING We 4 7K JUMP s PI f 59 V BLN yw 4 7K 40V is supplied to PIN1 of control circuit and the voltage is transformed into 5V by R814 0801 and C801 5V is controlled by V BLN S PIN V SIZE V POSI H SIZE H POSI VR output to 5 6 7 8 11 12 of CN801 adjusted H SIZE H POSI VR output to 5 6 7 8 11 12 of CN801 and controls IC301 SW801 functions as manual degaussing switch and the output is to PIN9 of CN801 via R817 VR801 is contrast control VR and outputs the voltage controlled into PIN2 of CN801 VR810 is sub contrast VR adjusts MAX value and VR809 controls MIN value 4 HORIZONTAL DRIVE CIRCUIT HORIZONTAL DRIVE CIRCUIT HORIZONTAL DRIVE OUTPUT HORIZONTAL DRIVE INPUT Horizontal drive pulse is applied to the gate 0402 C407 0406 and R407 form BIAS 16 KORTEK Corporation KT XX48 circuit 12V is supplied to T402 and PIN7 of T
15. servicing precautions and safety precaution always follow the safety precautions WARNING 2 A high voltage VR replaced in the wrong direction may cause excessive X RAY Emitting WARNING 3 An electrolytic capacitor installed which the wrong polarity might explode 1 Servicing precautions are printed on the label and should be followed closely 2 Always unplug the AC power cord from the AC power source before attempting to remove or reinstall any component or assembly disconnect PCB plugs or connectors connect all test Components in parallel which an electrolytic capacitor 3 After servicing always check that the screw components and wiring have been correctly reinstalled Make sure that the area around the serviced part has not been demaged 4 Check the insulation between the blades of the AC plug and accessible conductive parts example metal parts input terminals 5 Never touch any of the locked B voltage Do not apply AC power to the unit or any of its Assemblies unless all solid state heat sinks are correctly installed 6 Always connect a test instrument s ground lead to the instrument chassis ground before connecting the positive lead always remove the instrument s ground lead last KORTEK Corporation KT XX48 2 SOCKET PCB Circuit Description 1 VIDEO PRE AMP VIDEO PRE AMP 10UF 50V 49 R OUTPUT 1 3PF 50V 1 3PF 50V 1 3PF 50V 5
16. ven color Since the principle of the circuit operation is identical for R G and B RED circuit will be described as an example CRT CATHODE emits hot electrons when the voltage is supplied to the heater of and the temperature of the surface of adjacent CRT cathode reaches 900 and over Then the hot electron moves toward CRT FACE though there are some differences according to the conditions of voltage applied to GRID1 GRID2 GRID3 5 and the current is produced toward opposite way which shows up at CRT RED cathode SUB PCB PIN4 is connected with RED cathode passes through R962 and the changes in current and voltage occurs at the emitter of Q953 This changed current is displayed in the waveform and is sent to IC950 to amplify since it is very poor signal IC950 amplifies in R956 R957 R955 ratio and sends the signal to PIN3 of IC950 for secondary amplification The secondary amplification of IC950 is performed in R952 R964 ratio and the pulse is transformed into DC LEVEL by ZD950 and C952 Transformed DC voltage controls Q951 Q952 Q950 and is sent to SUB PCB PIN6 to control the base of Q953 When the base voltage of Q953 changes the voltage of emitter changes and controls the amount of hot electrons of CRT cathode 11 KORTEK Corporation KT XX48 The operation forms FEED BACK LOOP and maintains fixed value through repetition 5 PULSE GENERATOR PULSE GENERATOR 1
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