Received a Skyworth LCD TV model 32E55HM with three no issues—no display, no sound, and the indicator light not bright. The most common problem in this model is usually the backlight being dim or off. I first thought of replacing the booster tube. However, upon opening the case, I noticed that the warranty sticker had been tampered with, indicating it was previously repaired. I was worried about possible screen damage but decided to take a chance. After disassembling the unit, I found that there was no voltage on 5VS, 12V, or 24V. Removing the power board revealed that it had already been repaired before. The switch transistor 10N60 had three pins disconnected, and diodes D201 and D202 were damaged. After replacing them, other components seemed fine. I used a 13N60 as a replacement, but the power supply had noise. It turned out the new transistor’s parameters didn’t match. I replaced it again with a 10N60, but when I powered it on, there was a loud noise, and one leg of the transistor exploded. I then tried rubbing the motherboard and took some photos. Despite the new transistor showing no short circuits, further testing showed that ZD202, ZD205, R213, fuse, and switch transistor were all dead. The board had visible blackening. After installing a new 20N60 switch transistor, the voltage came back, and the power supply was quiet. The red light turned on, and I was relieved. But soon after, the TV wouldn't start unless pressed, and sometimes the red light would flash green for six seconds before returning to red. Measuring the voltages on the motherboard, U13 was at 2.6V, U10 at 2.6V, and U12 at 3.3V. When U10 dropped below 2.3V, the green light turned on. The CPU was hot, but using the formula from 8117, U13 was normal, while U10 should have been around 1.2V. After checking resistance values, I found that U13 measured 20 ohms, and U10 was only 8 ohms, with U12 and U10 having just 2 ohms between them. Even after removing the power transistor, the resistance didn’t change. Eventually, I concluded the CPU was faulty, and after replacing it, the resistance returned to normal. Three days later, the TV arrived, and I installed it. The red light was on, and the power button worked, but the screen kept turning on and off repeatedly. I removed the backlight cable and heard the boot sound. Testing the backlight, I found that two groups of LEDs lit up normally, and the display was clear. However, the third group shut down. Suspecting a problem with the backlight strip, I opened it, but everything looked normal. The next day, I was really frustrated. Further testing showed that when the power was cut, 5V, 12V, and 24V all dropped, so I suspected overvoltage protection. I disconnected the overvoltage circuit, and the voltage stabilized. Replacing components like 817 and 431 didn’t help. Finally, I replaced the TEA1733P chip, but nothing changed. At this point, I was desperate and even considered buying a new power board, but I wanted to find the root cause. I continued checking the peripheral circuits of the power IC and found no issues. Q304 was intact, and replacing the switch transistor didn’t help. My frustration grew, but I kept looking through the schematics. I noticed that the backlight could light two groups and stay stable, so I ruled out the backlight circuit. Then I focused on the power supply and noticed that the switch transistor’s fuse resistor had a value of 0.18 ohms, which was too low. I replaced it with a 0.39 ohm resistor, and to my surprise, everything worked. The backlight lit up fully without shutting down, and the TV was finally fixed. During final testing, I noticed that AV2 wasn’t working well, with a white image, while AV1 was normal. I checked the interface and saw signs of damage, possibly from a lightning strike. The user eventually sold the TV as scrap. Looking back, I realized the issue was simple but overlooked due to lack of experience. This repair took several days, and during that time, my wife gave birth to a baby boy, so I had to take a break. In the end, the fault wasn’t complicated, but missing one small detail made it frustrating. I hope this helps others who might face similar problems.
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