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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 issue was that there was sound but no image — the screen was completely black. Initially, I was told that there was no sound coming from the main board, so I suspected the problem might be with the power supply’s high-voltage board. The high-voltage board in this model is labeled as 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 within normal ranges. This led me to believe the problem was in the high-voltage inverter circuit responsible for powering the backlight. Upon further inspection, I found that transistors V704 and V705, along with the 3.15A fuse, were damaged.
I replaced those components, but the power failure persisted. Next, I checked the backlight control driver IC, N701, which is an OZ9976GN. I measured the 15th pin and found a short to ground, indicating that the IC was likely faulty. I also discovered that the protection resistor R745 had opened, and the power supply diode V701 was also damaged. 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 lit up for about one second before turning off again. I then checked the first and 16th pins of the OZ9976GN, where I found two Schottky diodes, VD702 and VD703, that were damaged. I replaced them with new BAT54C dual-diodes, but the issue still remained.
At this point, I suspected either a high-voltage or overcurrent protection issue. I first checked the 8th pin of the OZ9976GN, which is related to high-voltage protection. The signal from the lamp was fed into this pin through VD706 and R729. After checking these components, they all appeared to be in good condition. I temporarily connected a 1-ohm resistor to the 8th pin to bypass the protection, but the fault still existed, so I ruled out high-voltage protection.
Next, I focused on the overcurrent protection circuit, specifically the 9th pin. The return signal from the lamp was detected via VD711 and R728, and the protection was triggered by V703, controlled by VD704, R714, and V702. Upon testing, I found that the collector of V703 was leaking. I removed V703 and disconnected VD704 to release the overcurrent protection. When I powered the TV again, the screen lit up normally and stayed on.
To be thorough, I replaced V703 with a new PMBS3906 (PNP transistor) and tested the TV again. The screen remained illuminated without any issues. I left the TV running for five consecutive hours, and it worked perfectly throughout. The repair was complete.
This was a bit of a challenging repair, especially since I hadn’t posted anything like this before. I just wanted to share my experience and learn from others. If you have any suggestions or feedback, I’d really appreciate it.