Samsung LE37M87BDX turn on screech cycle when cold

[jesterace]

Hi, i have this samsung tv i'm learning to repair. I've read that on the LNXX models, the tantalum capacitor c102 failing can cause this symptom. The symptoms are that if the TV is cold, turning it on will result in a screeching from the speakers, a lot of colored lines and garble on the screen, then the TV goes back to standby and tries to turn itself on again. This cycle repeats. If left long enough, it warms up and you can watch the tv as normal as long as you like.

However, this is an LEXX model and i cannot see any tantalum capacitors on it at all. I am going to take some closeups of the main board as soon as i can and post them.

I wondered at first if anyone has come across this symptom that wasn't the common c102 capacitor? I guess on this mainboard they decided to use some standard electrolytic or solid can caps instead of one or more tantalums. I'm not sure at the moment as i have no schematic and only just started pulling the tv apart.

I can say that none of the caps on the power or main board are bloated/vented but there is some liquid (i wondered if it was flux or maybe leaking electrolyte??) near two aluminium electrolytic can caps.

Hope you can help, pictures to come very shortly!
James.

[jesterace]

Re: Samsung LE37M87BDX turn on screech cycle when cold

http://jm-server.no-ip.org/images/20161107_174606.jpg

http://jm-server.no-ip.org/images/20161107_174630.jpg

http://jm-server.no-ip.org/images/20161107_175003.jpg

http://jm-server.no-ip.org/images/20161107_175013.jpg

http://jm-server.no-ip.org/images/20161107_175033.jpg

http://jm-server.no-ip.org/images/20161107_175036.jpg

http://jm-server.no-ip.org/images/20161107_175046.jpg

http://jm-server.no-ip.org/images/20161107_175049.jpg

http://jm-server.no-ip.org/images/20161107_175053.jpg

http://jm-server.no-ip.org/images/20161107_175056.jpg

Pictures could be better, will retake in natural light tomorrow.

[jesterace]

Re: Samsung LE37M87BDX turn on screech cycle when cold

I've noticed there are two 47uf (16v or 10v? can't see 100%) solid can capacitors together near the big shield (top left corner of biggest shield in image 1). One reads 0.80ohms ESR and the other about 0.30ohms. The tantalums on other boards ive read about were 47uf i think? There is an identical 47uf cap near the back panel sockets that reads 0.15ohms ESR so maybe those two with higher ESR are the failing equivalent of the LN series tantalums?

[Hamie]

Re: Samsung LE37M87BDX turn on screech cycle when cold

Can't see your pictures however I repaired one of these fairly recently by replacing the 2 1000uf 10v caps on the mainboard under the heatsink.

Is the mainboard a bourdeux plus?

[jesterace]

Re: Samsung LE37M87BDX turn on screech cycle when cold

It says "tulip" on the big heat sink, apart from that i can only see model numbers. Pics should work?

EDIT: OOPS! Yes is does say bourdeux plus on one edge of the board, missed that. how did you discover the caps were gone?

[Hamie]

Re: Samsung LE37M87BDX turn on screech cycle when cold

Common fault on this board.
Worth changing them out.

[jesterace]

Re: Samsung LE37M87BDX turn on screech cycle when cold

Thanks, i'm going to take a look tonight. Just wondered how you figured out which ones were bad, i guess i could have tried a hair dryer over the board to narrow it down a bit...

[vinceroger69]

Re: Samsung LE37M87BDX turn on screech cycle when cold

This link has a picture of the capacitors that can cause this issue post 15 if you can i would replace them all thats under the sheild it may stop future failures.
https://www.badcaps.net/forum/showth...ht=heat+sheild

[Moreno83]

Re: Samsung LE37M87BDX turn on screech cycle when cold

Hairdryer does not really point out the faulty part because the heat travels to other components.

Does this tv also have a small board above the mainboard in the top right corner? It's a small board between the tcon and mainboard.

[jesterace]

Re: Samsung LE37M87BDX turn on screech cycle when cold

There isn't any small board as you describe, just psu, mainboard, inverter and tcon.

I removed the big shield/heatsink this evening and removed the 2 1000uf caps beneath. Both tested ok on an ESR meter and capacity meter. A couple of 47uf caps just outside of the shield tested bad >40ohms ESR when unsoldered so i've replaced those tonight. Then i thought it'd plug it up again after finding those two bad caps...but still the same problem.

When the tv decides to stay on after about 10 or 20 power up attempts, the picture quality on digital tv is awful (horizontal distortion like rewinding/fast forwarding a vhs tape). When the tv gets warmer, the picture improves to the point where the distortion is hardly noticeable - but still there a bit.

Actually ive just realized something... the picture distortion is ONLY on DTV. Also i found that if the source is NOT DTV, the tv will always power up first time. Switching to DTV or having the source left on DTV when powering up will start the problems off again.

So maybe the caps will be some that are related to the DTV tuner?

Might there be a way to pinpointing what caps might be the culprit, or is it a case of unsoldering the lot and testing with a meter?


P.S. i'm going to replace the two 1000uf's under the shield tomorrow, they seemed to test ok but I've now read so many more people having trouble with those causing standby and screeching issues that i guess i should replace them.

Thanks,
James.