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LG 50PB690 power supply terrible noise

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    LG 50PB690 power supply terrible noise

    I bought this TV with really bad oxidation on the power supply and bottom X boards, it was working but during pickup there was a lot of background noise so I don't know if it had this problem before.

    As soon as I could I opened the tv and started working on it, did not test it before since it had back bars on the screen and obvious signs of humidity. The X boards were replaced and the screen now works 100%, but the power supply...

    I washed the board and resoldered almost everything on the primary, the oxidation happened because of constant mains AC current flowing, so only the HOT side was bad, after hours of work I put it back, the TV fired up and after 5 minutes it started making a fizzling noise from near one of the transformers, seems like the VS/VA or the STR W6051S switching IC. It's not the 60Hz AC, more like random sparks.

    Scared as hell I pulled the plug and took a better look, but still after more soldering it lasts 2~10 seconds even without any board (auto start).

    The joints on the photos may look bad because after just 2 re-heats of the same spot the traces are lifting and I had to scrape and solder over the PCB to ensure good contact.
    All of the exposed copper was covered with a transparent insulant.

    So I do not want to keep testing the TV like this, every board is perfect except for the PSU. VA/VS voltages are fine and stable, the tv works and has image but with this noise originating from a high voltage section of the PSU it looks like something will blow up if I let it run any further.

    What can be done here? Which components can be removed so the noise can be isolated?
    Attached Files

    #2
    Re: LG 50PB690 power supply terrible noise

    It was some residue on one of the transformers. The one connected to the STR had absolutely corroded, TV was working still, even after fixing that and touching up the board a lot, it was still doing it. Decided to wash again and leave the board in the sun for 6 hours, same result, then put it in the oven at a low temperature(around 70C) for 1:30 hour and it worked, no more noise.
    Attached Files

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