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Konka LCD TV LC32TS86C power failure repair - appliance repair - Huaqiang Electronic Network
A few days ago, I repaired a Konka LC32TS86C LCD TV. The main issue was sound without image — the screen remained completely black. Initially, I suspected the main board, but after checking, there was no sound coming from it either. That led me to believe the problem was in the power supply’s high-voltage board. The high-voltage board model is 34080015 KIP+ L100U03C1.
At first glance, there were no obvious signs of burning or damage. I checked the PFC voltage and the 12V output, both of which were normal. This pointed me toward the high-voltage inverter circuit for the backlight. Upon further inspection, I found that V704, V705, and the 3.15A fuse had failed.
I tested other components like V708, R734, R732, R733, V709, R737, R735, and R736, and they all appeared to be in good condition. I replaced the original FET MDF5N50 with a new one, but the power failure still occurred. Next, I checked the backlight control driver IC, N701, which is an OZ9976GN.
I measured the 15th pin of the OZ9976GN and found a short to ground, indicating that the IC was damaged. I also noticed that the protection resistor R745 was open, and the power supply diode V701 had failed. I replaced the OZ9976GN with a new one, used a small enameled wire to bypass R745, and substituted V701 with a common LCD power MOSFET, FDN360.
After replacing these parts, the screen briefly turned on for about one second before shutting off again. I then checked the first and 16th pins of the OZ9976GN and found two Schottky diodes, VD702 and VD703, which were damaged. I replaced them with new BAT54C dual-diodes, but the TV still didn’t work properly.
At this point, I suspected either high-voltage or overcurrent protection was triggering. I first checked the 8th pin of the IC, which is related to high-voltage protection. The signal from the lamp was connected via VD706 and R729. After verifying that VD704, R729, and R712 were okay, I temporarily connected the 8th pin to ground using a 1-ohm resistor. However, the fault persisted, so I ruled out high-voltage protection.
Next, I examined the 9th pin, which is responsible for overcurrent protection. The lamp’s return signal was detected via VD711 and R728, and the protection was controlled by V703, VD704, and R714. During testing, I found that V703 had a leakage between its collector and emitter. I removed V703 and disconnected VD704 to disable the overcurrent protection. When I powered the TV back on, the screen lit up normally and stayed on.
To confirm the fix, I replaced V703 with a new PMBS3906 (PNP transistor) and tested the TV again. It worked perfectly, with no shutdown issues. I left the TV running for five continuous hours to ensure stability, and everything functioned as expected.
This repair took some time and required multiple component replacements, but eventually, the problem was resolved. I just finished organizing the repair process and wanted to share it with you. It's my first time posting, so I hope this helps others facing similar issues. Any feedback or suggestions would be greatly appreciated.