I recently received a Changhong HP4388 rear-projection TV with a black screen, no sound, and no display. All remote control functions worked normally. When I first turned it on, I could hear the sound briefly, and the same issue occurred when using the DVD. The picture-in-picture feature was also completely black. At first, I considered disassembling the unit to check the digital board. But before that, I connected the DVD player directly to another TV via the rear-projection's audio and video outputs. The second TV had sound but no image, which confirmed the issue wasn't with the DVD player.
To narrow down the problem, I connected the main tuner's video output directly to the AV conversion block (M52472). The screen showed an image, though it was blurry. This suggested the issue was in the conversion part. I replaced the picture-in-picture conversion block, but the screen remained black. That was unexpected — I thought the problem was fixed. I bought two new conversion blocks and installed them. Finally, the image appeared, and I was relieved. My heart was full of joy. It turned out both conversion blocks were faulty.
After that, I checked the digital board, which was easy to diagnose once the initial issue was resolved. I want to thank Dongguan Guanjia 123 for uploading the original schematics, which helped me find the problem quickly. When I returned the TV to the user the day before yesterday, they mentioned that the picture-in-picture had been broken for a year and hadn’t affected their use. However, this small issue almost led me to mistakenly blame the digital board.
One end of the cable connects to the main tuner’s video output, while the other connects to the video output pin of the conversion block.
![One end of this line is connected to the main tuner video output, and the other end is connected to the conversion block video output pin.]
In TV mode, the sound works fine, but there's no image. The image appears to be out of sync with the intermediate frequency or the horizontal scan.
![In the TV state, the sound is fine-tuned with no image, and the image looks like the intermediate frequency is out of sync or the line is not synchronized.]
The main picture conversion block has just been replaced.
![The main picture conversion block, one side is just replaced.]
This is the small picture.
![This is a small picture.]
The image is now normal, and the picture-in-picture function is working correctly.
![The image is normal, and the picture-in-picture is correct.]
These two faulty components were the real culprits.
![These two bad guys.]
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