Sharp LCD TV LCD-32Z100A does not boot fault repair example - appliance repair - Huaqiang electronic network

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I was working on repairing a Sharp LCD-32Z100A LCD TV. The main issue was that the TV wouldn't turn on — no power, and the indicator light didn’t illuminate. After disassembling the unit, I checked the fuse, and it was intact. The voltage across the main capacitor was 320V, but there was no output voltage from any of the power channels. Further investigation revealed that pin 1 of the power IC7002 (NCP1230) was shorted to ground. Even after disconnecting pin 1, the board still showed a short to ground, which led me to check other components.

I then found that pin 8 of IC7001 (NCP1606A), a PFC power factor correction chip, was also shorted to ground. I replaced IC7001 with a new NCP1606A, and the indicator light turned on. However, the main capacitor still only reached 320V, and there was no boost in the output voltages. The 12V rail was missing, while the 24V was normal. I let the unit run for about half an hour without any issues, but I wasn’t fully confident yet. So I decided to focus on fixing the PFC circuit more thoroughly.

Since I didn’t have an NCP1606A on hand, I tried using an NCP1653A from an old board. I assumed the function was similar, so I soldered it in place. However, the main capacitor still only charged to 320V. I continued checking the circuit and found that Q7001, a MOSFET transistor, had failed. I replaced it with an A1015, but the problem persisted — the voltage remained at 320V, and the system still wouldn’t boot properly.

I then checked the voltage at pin 1 of the NCP1606A and found no input. That led me to inspect the resistors R7024, R7025, and R7026, all of which were 1.2MΩ. During testing, R7024 measured only 66KΩ. After resoldering, the resistance returned to normal, but the other two resistors were fine. Despite this, the fault remained unresolved.

At this point, I decided to replace all three resistors. Finding such high-value resistors was challenging, but I managed to find two 8.2MΩ resistors and tested them in parallel. The capacitor voltage increased to 450V, which was too high, so I quickly shut down the unit. After removing the resistors and testing again, I found a combination of a 2MΩ, 1MΩ, and 510KΩ resistor. I soldered these in place, and the TV finally worked correctly. The voltage across the capacitor stabilized at 387V, and the outputs were normal. The repair was successful.