Xiahua plasma TV PS-42K8 soundless maintenance example - appliance repair - Huaqiang electronic network

Fault Phenomenon: There is sound, but no picture (no grating).
Diagnosis and Repair Process: Initially, the output voltage of each power supply board was checked, and it was found that there was no Vs voltage, while other voltages were normal. After disconnecting the Y board, the Z board still showed no Vs voltage output. At first, no obvious damage was found on the Y and Z boards, so the problem was suspected to be with the power board.

The power board was tested for short circuits, but no visible damage or burning was observed. A large area re-soldering was performed on the power board, and after testing, the screen appeared normally. However, the issue returned after some time, with the screen going black again. Further investigation revealed that the voltage at pin 1 of IC203 (IR2109) was low at -14V, which is supplied by IC202 (KA7815). After re-soldering both IC202 and IC203, the screen worked again, but only temporarily.

It was then suspected that the filter capacitors C222 and C223 associated with KA7815 might be unstable due to high temperature. These capacitors were replaced, but the issue persisted. Further checks showed that pin 1 of IC203 had 14V, but pins 2 and 3 had no driving voltage, pin 4 was grounded, pin 5 had 13V, pin 6 had 10V, pin 7 had 12V, and pin 8 had 16V (the expected value for pin 8 should be around 24V, but the measured voltage was 75V in this case). This indicated a potential fault in the drive unit CN8100. Since the board couldn’t be repaired without removing the driver plate, it was carefully disassembled and re-soldered. After reassembly, the TV operated normally, and repeated tests confirmed the fix.

Important Note: This board is a double-sided PCB, so care must be taken during disassembly. Improper handling can damage the holes, leading to more complex repair issues later.