Plasma LG 50PK550 picture blanks only when hung on wall

[RCKadath]

Hi,

I have a 3 years old LG 50PK550 tv that has an intermittent problem. After usually about 5 minutes, the picture starts to flicker and shortly thereafter, it goes blank. The sound still works however. This has been going on for only a week or two.

Here's a little background info that might or might not help. I hung the TV on a wall this summer. About 1-2 months ago, it started making a buzzing sound, correlated to the amount of white in the image (more white = louder buzzing). I read that applying pressure to the back sometimes solves this, so I squeezed a piece of foam between the wall and the TV, and it indeed helped.

Another bit of info is that 3-4 weeks ago we had lighting strikes around our house. At some point during the storm, the TV developed horizontal lines and an overall bad picture. I thought it was toast but a power cycle fixed it. It remained fine for about two weeks after that.

Here's the troubleshooting that I've done so far:
- Removed the TV from the wall and put it on its stand
- Checked the VA and VS voltages on the power supply. VA is 60V but VS is 202V (supposed to be 201V on the sticker). I don't trust my cheap voltmeter to adjust the voltage however. I'll borrow a Fluke from work tomorrow and check again.
- The TV is actually working fine when resting on the floor and not hung on the wall! It's been 2-3 hours now and everything is fine.

Hypothesis #1:
Hanging the TV on the wall is somehow causing stress in one of the PCBs making if fail. Doesn't quite explain why it would work the first 5 minutes though.

Hypothesis #2:
Removing the back panel decreases overall temperatures and it never reaches the point at which it fails.

I'd appreciate pointers to continue my investigation. I somehow need to make the TV fail again to continue troubleshooting but I can't troubleshoot when it's hanging on the wall... I'll try to simply put the back panel back on to see if it starts failing again.

[tom66]

Re: Plasma LG 50PK550 picture blanks only when hung on wall

It is quite likely there is a temperature sensitive component.

What you can do is take something like a hairdryer and start heating up parts of the set. If you find a part which causes it to go wrong when heated, then you have found the source of the problem.

[retiredcaps]

Re: Plasma LG 50PK550 picture blanks only when hung on wall

Tom66 is the plasma expert.

Some ideas until he responds.

1) You can try using a hair dryer with the back case off and gently heating up portions of the board to see if the picture blanks?

2) Try feeding the TV an all white picture source. I believe white causes the plasma to consumer more power.

3) See if you can borrow a IR temperature gun?

edit: Tom66 apparently types faster than I.

[RCKadath]

Re: Plasma LG 50PK550 picture blanks only when hung on wall

Thanks guys, I will try with a heat gun tomorrow. Tonight I gotta watch the last episode of Game of Thrones now that I found a way to make the TV work temporarily

[capkid]

Re: Plasma LG 50PK550 picture blanks only when hung on wall

Uh, I wouldn't use a heat gun. I'd use a hair dryer instead.

[retiredcaps]

Re: Plasma LG 50PK550 picture blanks only when hung on wall

Uh, I wouldn't use a heat gun. I'd use a hair dryer instead.

RCKadath lives in Quebec. Thus there is a possibility of "lost in translation". Don't worry, RCKadath will know what I'm talking about!

PS. A heat gun will likely destroy/kill the capacitors on the board.

[RCKadath]

Re: Plasma LG 50PK550 picture blanks only when hung on wall

I'm sorry to revive an old thread but for the benefit of Google, I wanted to post the outcome. It appears that it was indeed what I thought, hanging the TV on the wall had caused stress on the PCBs and an audible noise.

What I did to fix it was somehow impose the same stress to the TV when hung on the wall, unscrew all screws to get the PCBs to be stress-free and then rescrew everything. It worked.

The hardest part was figuring out how to hang the TV from the mounting screws while having access to the electronics. I did it by hanging the TV with ropes on the ceiling. My wife had a good laugh with that... I did take a picture but too lazy to extract it from my phone at the momment. I'll post it if there's interest.

Anyhow, it's been 2 months now and no more problems, so I'm quite confident in my fix. Thanks to everyone for your help.