I was working on a Hisense 25 machine, but I can't remember the exact model. The issue was that the display wasn’t bright enough. After opening the case, I checked the power supply and found it to be mostly normal, except that the 12V output from the switching power supply was slightly low. When I disconnected the load, the voltage returned to normal, which made me suspect a short circuit in the 12V line. Since there were no schematics available, I used a multimeter to trace the circuit. I noticed that two voltage regulators, 7808 and 7805, were connected in series. The output of the 7808 was only around 6V, while the 7805 had almost no voltage. When I disconnected the 7805, the 8V output came back to normal. But when I reconnected it, the heatsink got extremely hot, indicating a short circuit. I followed the wiring toward the 9373 chip and found that the power pin of the 9373 had no voltage. After checking again, I discovered that the tuner’s power supply (5V) was still not working. Then I tested the crossover line to the high-frequency head and found that the voltage was normal. However, there was an electrolytic capacitor (16V/100UF) along with two small ceramic capacitors between the crossover and the high-frequency head. Considering that ceramic capacitors rarely fail under low voltage, I decided to test the electrolytic one. It turned out to be shorted. After replacing it, the screen finally showed up, and the machine worked properly. This was a rare case where a faulty filter capacitor caused the problem, and it was located near the high-frequency section rather than the main power supply. It's easy to overlook such components, but they can cause significant issues if not checked thoroughly.
Manual Lifting Column,Lifting Machine,Lift Mechanism,Linear Lifting Mechanism
Kunshan Zeitech Mechanical & Electrical Technology Co., Ltd , https://www.zeithe.com