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

Fault phenomenon: There is sound, but no picture (no grating). Overhaul process: Initially checked the output voltages of each power supply board and found that there was no Vs voltage, while other voltages were normal. After disconnecting the Y board, the Z board still didn’t show any Vs voltage. At first, no obvious failure was found on the Y and Z boards, so we concluded that the power board was faulty. The power board showed no visible short circuits or burn marks during inspection. We performed a re-soldering on the large area of the power board, and the screen returned to normal. However, after some time, the screen went black again. This led us to suspect that there might be a poor contact or unstable components. Further testing revealed that the PFC voltage of 380V was normal, but the voltage at pin 1 of IC203 (IR2109) was only -14V, which was relatively low. This pin is powered by IC202 (KA7815). After re-soldering both IC202 and IC203, the screen came back to normal. But after a while, it turned black again. We then suspected that the filter capacitors C222 and C223 connected to KA7815 might be unstable due to high temperature. These 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. According to data sheets, pin 8 should have around 24V, but our measurement showed 75V. This discrepancy raised concerns about the drive unit CN8100. Since the board couldn’t be repaired without removing the driver plate, we carefully took it off and re-soldered the connections. After reassembly, the test machine worked normally with a stable image. A key reminder: this is a double-sided PCB, so disassembling must be done carefully. If not handled properly, it can damage the holes and cause more issues down the line.