Changhong plasma TV 3D42A3700I does not shine fault repair - Home Appliances

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One day, a middle-aged woman came into the store and asked if I could repair her LCD TV. I asked for the size, and she said "42". I immediately agreed, saying that the front section had already found someone to replace the board, and it would cost over 900 yuan, with only the machine included. I was shocked (I wasn't sure if local repair fees had gone up so much). Later on... I scheduled a time to go to her house. At first glance, the TV screen looked faintly white, which made me think there might be some fraud. Looking at the back, it turned out to be a plasma TV, not an LCD! I didn’t know how to fix plasma TVs, but I didn’t want to pay so much for a repair. When I turned it on, the power indicator blinked a few times and then went off, and there was no further response. She mentioned that the front section could still turn on occasionally, but after several attempts, it wouldn’t light up at all anymore.

I did a preliminary inspection and saw no signs of prior repairs. The motherboard seemed to be the issue. I told her to bring it back to the store for further testing. If we couldn’t fix it, we’d have to increase the price.

When I brought it back, I checked online and found very little information about plasma TVs. The screen model was Samsung S43AX-YB01/YD01, and I couldn’t find the self-test method. After trying several methods, nothing worked. I measured the power board's 5VSB voltage and noticed it was unstable. The motherboard sent a normal boot signal, and other voltages were okay, but the VS and VA voltages dropped to nearly zero, and PS-ON went high. Forcing a boot also didn’t work. Repeatedly plugging and unplugging cables didn’t help. When I unplugged certain cables, the VS voltage didn’t rise. During a power-on test, I heard a “click” sound, and the Y-board screw wasn’t in place. After checking, I found that one IGBT on the Y-board was shorted, and several fuses were open. I suspected the power board was faulty, but even replacing it didn’t solve the problem. Some online sources said the power board was modified, so I went back to the same supplier and got an old Y-board, replacing the IGBT. After installing it, the machine booted up, played music, and showed a signal. But after a few tests, the new IGBTs burned again. I was really frustrated, and the customer kept calling me every day.

I considered buying a full set of boards from Taobao (like XYZ or something), and even though it was an older version, I thought I could fix it as long as the screen was fine. Finally, I decided to return the broken Y-board and get a replacement. I contacted the seller, apologized, and said I would exchange it right away. I tested the new Y-board and found it working perfectly. I returned the faulty one and sent the repaired TV to the customer the next day. After several hours of testing, everything was normal. I finally felt relieved.

This was my first time repairing a plasma TV, and it was quite embarrassing. I suspect the power board had already been damaged before, and I accidentally broke the Y-board. It was awkward, but I managed to fix it with some help from forums. In the end, I charged the customer a reasonable fee and didn’t lose money.

For beginners, here are some key takeaways:

• Don’t quote prices for plasma TVs. The Y-board is expensive and often problematic. Many issues can’t be easily identified without proper tools.
• Test the power board separately. Ground PS-ON, connect VS to D5.3V, and use a 100W bulb to check load capacity. Make sure all outputs are stable.
• Some boards must be properly connected during testing. Otherwise, serious damage can occur. This particular Y-board required all ground connections and had fuse resistors.
• If you’re unsure about the screen’s self-test method, don’t try it. Some cables may burn the board if disconnected improperly. Always wait for the voltage to drop before reinserting them.