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 with the issue of "three no"—no power, no display, and the indicator light not turning on. After disassembling the unit, I found that the fuse was intact, and the voltage across the main capacitor was 320V. However, there was no voltage output from any of the power channels. Further inspection revealed that pin 1 of the power IC7002 (NCP1230) was shorted to ground. I disconnected pin 1, but it still showed a short, so I decided to check other components. I then discovered that the PFC chip IC7001 (NCP1606A) had a short at pin 8 to ground. I replaced the IC7001 with a new NCP1606A, and after powering up, the indicator light turned on, but the voltage across the main capacitor remained at 320V without boosting. The 12V and 24V outputs were normal, but the system didn’t seem stable. I monitored it for about 30 minutes without issues, but I wasn't fully confident yet. To be safe, I decided to fix the PFC circuit. Unfortunately, I didn’t have an NCP1606A available, so I used an NCP1653A from an old board. I assumed the pin functions were similar. After soldering, the main capacitor still showed 320V, so I continued testing. I checked the voltage at pin 1 of the NCP1606A and found no voltage. Then I measured resistors R7024, R7025, and R7026, which are all 1.2MΩ. R7024 showed only 66kΩ when measured in-circuit. After replacing it, the resistance value became normal, but the other two resistors were also replaced just to be safe. After reassembling, the issue persisted. I tried replacing the three resistors, but high-value resistors are hard to find. I ended up using two 8.2MΩ resistors in parallel for testing. The voltage across the capacitor increased to 450V, so I quickly shut down the device. Upon further testing, I found that the resistors were actually 1MΩ, 300kΩ, and 510kΩ in series. The test voltage stabilized at 387V, which was normal. Finally, I removed the resistors in series and replaced them with a 2MΩ, 1MΩ, and 510kΩ chip resistor. After soldering everything back, the TV worked perfectly. It was a tough repair, but it paid off in the end.