I recently received a Changhong HP4388 rear-projection TV with a black screen, no sound, and no display on the remote control. However, I could hear a brief sound during startup, and the same issue occurred when using the DVD player. The picture-in-picture feature was also completely black. Initially, I thought it might be a problem with the digital board, so I decided to test it further.
I connected the DVD player to another TV via the rear-projection’s audio and video outputs. The second TV had sound but no image, which made me think the issue was with the main unit. To narrow it down, I directly connected the main tuner’s video output to the AV conversion block (M52472). At that point, the screen showed an image, though it was blurry. This suggested the problem was in the conversion section.
I replaced the picture-in-picture conversion block, but the screen remained black. That was confusing—was there another fault? I bought two new conversion blocks and installed them. Finally, the image appeared again, and I was relieved. It turned out both original conversion blocks were faulty.
After fixing the issue, I checked the digital board to make sure everything was working properly. Fortunately, it wasn’t too complicated once the main problem was identified. A big thank you to Dongguan Guanjia 123 for uploading the original schematics, which helped speed up the diagnosis.
When the TV was returned to the user the day before yesterday, they mentioned that the picture-in-picture had been broken for a year and didn’t affect their experience much. Still, this small issue almost led me to misdiagnose the problem as a digital board failure.
One end of the video cable was connected to the main tuner's output, while the other was connected to the conversion block’s video input pin.
In TV mode, the sound was fine, but there was no image. The image looked like it was out of sync, possibly due to an intermediate frequency or line synchronization issue.
The main picture conversion block had just been replaced.
This is the small picture.
The image now looks normal, and the picture-in-picture function is working correctly.
These were the two faulty components.
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