This repair involved a Haier TV that initially had a power supply voltage issue. I used a light bulb as a load during testing, but made a mistake while handling the high-voltage package. After discussing with the customer (who was quite frustrated), we decided to replace the high-voltage module. When the TV was first brought in, it wouldn’t boot, and the power indicator didn’t light up. The cover was powered on, and the measured voltage dropped from 125V to 0V. At first, I suspected the +B filter capacitor. However, when I used a 100W bulb as a load, the boot light turned on, and the +B voltage stabilized at 125V. Testing the B pole showed a voltage of about 0.5V, which led me to conclude that the high-voltage package was faulty. After replacing the high-voltage module, the same issue persisted. It turned out that the problem wasn’t with the high-voltage module itself, but rather with the voltage regulation circuit. The power chip, STR G9656, was outputting voltage, so the power block was functioning properly. This pointed toward an issue in the feedback or control section. I immediately checked the KA431 voltage regulator and found a short between pins 1 and 2. After removing it, I confirmed that pins 1 and 2 were shorted, while pins 3, 1, and 2 were open. I replaced the KA431, and also suspected the optocoupler might be faulty. Upon testing, I found a short between pins 3 and 4, which measured around 20K ohms. I replaced the optocoupler as well. After rechecking all components online, everything seemed okay. I then used the bulb as a load again and measured the +B voltage, which now read 140V — and that’s actually normal for this model. Once the bulb was disconnected and the circuit restored, I powered on the TV. A picture appeared, the AV signal worked, and both the audio and video were clear and normal.
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