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Plasma TV keeps shutting off - LG 50PN6500

Hello,

My plasma TV (LG 50PN6500) developed and issue some time ago.

Symptoms: While watching, the TV would turn itself off periodically. While off, it does not respond to any commands (IR remote or physical buttons on the TV itself). Unplugging the TV from power doesn’t help. The TV turns itself on in about 5-10 minutes. This continues endlessly (ON for about 15-30 minutes, OFF for about 5-10 minutes). While in ON state, everything works normally, while in OFF state, it looks like in standby mode - screen off, red standby LED lit, just not turning on.

Troubleshooting: I popped the back cover off to see if there is an obvious issue. Could not see anything wrong with any of the components at a quick glance. No bulged or leaking capacitors, no obvious discoloration on PCBs. While I had the back cover off I noticed that the issue disappeared. I had it without a cover for over a week and it didn’t happen a single time. To me, it seems that something is overheating and that’s why TV keeps shutting off.

Question: Anyone has an idea which component or which part of the PCB it could be? I understand that I could probably cut a hole to the back cover for a PC case fan, but I would prefer a more permanent and nicer fix if possible.

I am attaching photos of the PCBs.

Thank you

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I know this is almost a year old but I have the exact TV model with the same issue! I even tried removing the back cover and the problem seems to go away. My other 50” LG plasma is a slightly different model and does not have this over heating issue.

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Hi @teh_beatman ,

To me there seems to be heat discolouration showing on the board in the 3rd image down.

The one with the silver heatsink with the "rework" sticker on it. Up the top end, right side, between the large capacitor and the next capacitor down and to the left of the small cable that connects the two boards together.

It may just be the light when the picture was taken as it is more noticeable in the 3rd image than in the 2nd image down showing the same board area

I don’t know the answer but here’s the service manual for the TV, that may help as it has the schematics. It is free but awkward to use online as you have to change the page number below the document and click Go every time that you want to turn the page. To download the manual you have to register with the website.

Hopefully a start.

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Hello, I just want to post an update on my issue.

Thank you @jayeff for your ideas and also for the service manual. I did go through it and try to see what could be the issue but to no avail. So I used the TV w/o the back cover for some time. Unfortunately, the same problem came back even when the cover was off.

This time around I was able to find the culprit as I came up with the idea to test each board with a hairdyer. As soon as I start blowing hot air directly on the signal processing board the TV turned off immediately. So I’m pretty sure that the overheating element is the microprocessor labeled IC400. It is LGE2111C-MS or some variant of it. Right now I have a silent PC case fan @5V pointed at it and the problem stopped so I’m pretty confident that this is what is causing the problem.

I’m waiting for a slightly larger heatsink from Ali and I’m hoping that a larger heatsink area combined with a new thermal paste should be enough and no external fan will be necessary. Unfortunately, the back cover sits flush with the connectors on that board so I am limited with the size of that heatsink.

Maybe this helps anyone with the same problem.

Edit*

quick update: it was not the microprocessor, even with the upgraded heatsink, the issue still persists. It is definitely something on that signal board but I could not find out what exactly. I thought it is a LDO regulator next to the S/PDIF connector as that area was quickest to react to hot air but after reflowing the solder joints the issue is still there. I also measured the voltage of that and others regulators when the TV is off but all read good voltages.

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You are a genius ! I put a fan on the main board for testing. The back cover is in place. For the moment : it works !!!

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For me it was diode D400 (BAW56) on main AV board - near SPDIF above LDO actually as mentioned before. When heated it goes open circuit, after replacement TV is working fine again :) . Based on schematic it is something to do with CPU reset circuit.

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