Hisense color TV does not boot a special failure example - Appliances

DFN1006 TP-RCLAMP3321P ESD Diode Low Capacitance

Filter 18.432M

I was working on a Hisense 25 machine, but I can't remember the exact model number. The main issue was that the display wasn’t bright, and the machine uses a 9373 super chip. After opening the cover, I checked the power supply and it seemed mostly normal, but the 12V output from the switching power supply was slightly lower than expected. When I disconnected the load, the voltage returned to normal, which made me suspect there might be a short circuit in the 12V line. Since there were no schematics available, I used a multimeter to trace the voltage paths. I found that the 7808 and 7805 voltage regulators were connected in series, with the 7808 supplying power to the 7805. However, the output of the 7808 was only around 6V, and the 7805 had almost no voltage. When I disconnected the 7805, the 8V output from the 7808 came back to normal. But when I reconnected the 7805, the heat sink became extremely hot, indicating a possible short circuit. I carefully traced the wiring toward the 9373 chip and noticed something strange — the power pin of the 9373 had no voltage. After checking again, I realized the tuner’s power supply (the 5V line) was disconnected. I then moved along the wiring and eventually found another path leading to the tuner. At this point, I decided to disconnect the tuner's power supply and check the voltage again. It was still 0V, so I moved to the crossover line of the tuner. There, the voltage was normal. The next step was to inspect the components between the crossover and the high-frequency head. There were two small ceramic capacitors and one electrolytic capacitor (16V/100UF). Given that ceramic capacitors are less likely to fail under low voltage, I focused on the electrolytic one. After removing it, I tested it and found that it had failed — it was completely shorted. Replacing it restored the voltage, and the picture finally appeared on the screen. After testing, the machine worked perfectly. This case highlights how often capacitor failures cause issues, especially in the power supply section. However, in this situation, the failure was located near the high-frequency head, which is an unusual spot. It’s easy to overlook such components, but they can lead to serious problems if not checked thoroughly. Always take your time and don’t skip any steps, even if things seem straightforward.