Have you ever encountered a very [special] fault? ? ? - appliance repair - Huaqiang Electronic Network

Probe current voltage pin 290*3600, needle head diameter is 3.5mm, can be too large

MOS power IC full range

Photocoupler

Today, I received a 50-inch SAMSUNG PDP TV model PN50B450B1D. When I turned it on for testing, the standby light flashed and there was a relay "drip-drip" sound, along with a humming noise. Pressing the power button or using the remote control had no response at all. So, I took off the back cover and started troubleshooting. I decided to focus on the power board first. I disconnected all the cables from the power board, including the screen cable, then connected a 220V 100W bulb as a dummy load to the VS output. I also added a 2K resistor between the STBY and VS-ON, and shorted PS-ON to ground. This allowed the power board to run independently. I quickly checked the voltages: 5V, 15V, VS 207V, and VA 54V — everything looked good, and the bulb lit up normally. Great! The power board was working fine. Next, I reconnected all the cables. When I connected the Y board and the Y buffer board, the relay in the power board clicked once and then protected itself. It clicked again — clearly, the issue was with the Y buffer board. I removed the buffer board and plugged in the Z board. Immediately, the power board protected again. I took out the Z board and found two STK1820 chips and two FGPF50N33 transistors that were damaged. I replaced them, but the problem wasn't fully fixed yet. After this, I felt relieved and had a cup of tea. Then I went to the warehouse, got the necessary parts, and started installing them one by one. To my surprise, the image appeared! I sat on the sofa, sipped my tea, and watched the show — feeling proud. But just as I was getting comfortable, I noticed something strange. The image had some distortion — like a snow effect. I blinked a few times, and realized it was a bit of a “flower screen” (a common term for image noise). My excitement faded a little. At that point, I thought maybe the Y board was still faulty, or perhaps the Z board wasn’t fully repaired. I tried adjusting both boards, but the image quality didn’t improve. So I removed the Z board again and checked it carefully. While I was at it, I also reconnected the Y board. To my surprise, the image came back even without the Z board — and the quality was the same as before! That really confused me. Then I realized — the original problem was definitely in the Z board! After checking further, I found that the Z board had an RJH3044 transistor that had been replaced. I used a similar one from a dismantled unit and installed it. Finally, the HD image came back clearly. I was so excited! I’ve fixed similar TVs before, but this time, I missed a chance to share my experience with others. I feel bad about that. This case taught me not to be misled by initial symptoms. Even without the Z board, a plasma TV can display images and sound. What a “high-tech” Samsung plasma TV! From my perspective, it’s not very practical these days. If you don’t test it yourself, you can’t be sure. Masters, what have you experienced during your repair journey? I’d love to hear your stories and learn from you. Thank you all for reading!