Samsung LCD Power Board turning on and off.

[dcapper]

Re: Samsung LCD Power Board turning on and off.

My turn to ask for help. I retouched almost every solder joint. I metered all diodes and caps out of circuit, including the large cap. I metered the transistors as well, no shorts, including QM801 and QM802. No power just a standby light. Has anyone ever had to replace the 817N chips? There is 4 on the board. I had an Emerson power supply that they were blown. Or should I be ordering a repair kit with the MC33067P chip?

[Vilpo]

Re: Samsung LCD Power Board turning on and off.

My pleasure....sounds like a common manufacturing defect. Nice work John!!

Hi guys. I just wanted to let you know, had the same issue with Samsung tv, power board bn44-0214a. Tv would turn on/off by itself, and sometimes would not turn on at all..
Ordered a cap repair kit on ebay and replacing caps would not fix the problem.
Then, i found this topic and more carefully inspected the solder joints.. And what do you know, a bad solder on QB802, one of the legs had a circular crack in the solder.
I desoldered, put new solder on the legs and now tv works like normal!
Thanks guys for this awesome find!

[waitery]

Re: Samsung LCD Power Board turning on and off.

Exactly my problem!

Checked the QB801 and QB802 and found one tiny circle crack around the pin.
It wobbled a bit when I wiggled the transistor. Touched up the solder and perfect operation. It's been going for a week now.

Thanks a bunch for posting this, I would have replaced all the caps otherwise and then gotten frustrated by no no success.

John

My pleasure....sounds like a common manufacturing defect. Nice work John!!

[Engineer John]

Re: Samsung LCD Power Board turning on and off.

....turned on and off randomly. The power board is BN44-00214A and it had no bulging capacitors.

John

[Engineer John]

Re: Samsung LCD Power Board turning on and off.

OK guys, we're watching TV! Cold solder joint found on Fairchild Mosfet located at QB802, just a step passed PC802S. I just kept getting these huge voltage swings at PC802, so I started backtracking and when I got to the FET and I touched it with my Fluke probe to get a reading and it was just enough pressure to start the TV without me having to press the on/off switch.....so thrilled! The joint was super weak looking before reworking it and applying three new beads of solder.

Looks like she is holding steady, voltages all look good and there seem to be no problems. It fires up perfectly every time I hit the remote and touch the set's power button. I am going to burn test it to make sure that we have the issue buttoned up.

Retired and PlainBill, THANK YOU SO MUCH for your help, patience and most of all, YOUR TIME! I would love to sit down and troubleshoot with you guys one on one! I appreciate you both!!

Exactly my problem!

Checked the QB801 and QB802 and found one tiny circle crack around the pin.
It wobbled a bit when I wiggled the transistor. Touched up the solder and perfect operation. It's been going for a week now.

Thanks a bunch for posting this, I would have replaced all the caps otherwise and then gotten frustrated by no no success.

John

[mmartell]

Re: Samsung LCD Power Board turning on and off.

I know this is an old thread but wanted to add my appreciation. Resoldering QB802 indeed fixed my startup problem.

Funny thing is it didn't even look bad under my magnifier but I added solder to all three pins. On one pin I put a fair amount of solder and when I checked my work thwre was still a large part that had no solder. I thought where the hell did it go ? Added more and then all was good. Cheers!

[jsaily]

Re: Samsung LCD Power Board turning on and off.

I would have replaced 'em all but did not have the 3300uF cap. They measured ok though, and the TV boots up nicely this morning too. I have some cap values on order now and will replace the rest if the tv comes back to me :-)

[budm]

Re: Samsung LCD Power Board turning on and off.

I would suggest to replace the caps as a set.

[jsaily]

Re: Samsung LCD Power Board turning on and off.

I worked on a Samsung LE32A465 from my friend which turned on and off randomly. The power board is BN44-00214A and it had one bulging capacitor, the 2200uF / 10V connected to the stand by circuit. Its ESR value was actually not as bad as I thought, about 0.6 ohms. Replaced it with Panasonic low-ESR type. Other caps measured good, close to zero ESR. The TV turned on, and stayed on for a few hours without problems so I gave it back yesterday.

Today it didn't start again, and I found this thread about the dried up solder joint plague on these boards. I resoldered all MOSFETs, diodes and ICs, and now it's holding up again without problems. Will try again tomorrow morning if the bugger will cold start.

[adambutt]

Re: Samsung LCD Power Board turning on and off.

Hi ,
I had the same problem and my tv is working perfect now after re soldering all the FETs . I think after few year the soldring gets rough . I did not have to change any capacitors . So thanks for your post


If anyone can't fix their Tv after changing the capacitors try ro re solder the main ICs , FETs and other components
It should be fix
......

[adambutt]

Re: Samsung LCD Power Board turning on and off.

Hey Guys looking for some help I have a 32' Samsung Model #LN32A450 with a power board Dong Yang MK32P5B, this unit runs for about 30 mins and then shuts off, and it will always restart right away....I replaced all the electrolytic caps 13 of them and I am still having the same issue, can anyone suggest any other component that might causing the issue...Please let me know and Thanks for reading my post.

Re: Samsung LCD Power Board turning on and off.
Hi,
First of all thanks for all your posts and team work
I am mobile phone repairer and know a bit about electronics recently my uncles samsung tv got fault . The red light on the front blink 3 or sometime six times and no display . I took the power board out clean it with rubbing alcohol dry it and it start working after few days it again stopped working . I checked few forms and every one was saying change the capacitors but there was no leak or blown caps in my power supply . So what I did re clean the power supply board with rubbing alcohol and re-solder all the ICs , transistors, FETs , inverters and all the main components . After that I turned the tv and it is working fine . I did not have to change and caps or any thing



I would suggest to every one who is having this blinking light problem and can't see any blown or faulty caps please re heat or re solder your FETs and main components may be there is cold solder or any lose connection
Thanks

[adambutt]

Re: Samsung LCD Power Board turning on and off.

Hi,
First of all thanks for all your posts and team work
I am mobile phone repairer and know a bit about electronics recently my uncles samsung tv got fault . The red light on the front blink 3 or sometime six times and no display . I took the power board out clean it with rubbing alcohol dry it and it start working after few days it again stopped working . I checked few forms and every one was saying change the capacitors but there was no leak or blown caps in my power supply . So what I did re clean the power supply board with rubbing alcohol and re-solder all the ICs , transistors, FETs , inverters and all the main components . After that I turned the tv and it is working fine . I did not have to change and caps or any thing



I would suggest to every one who is having this blinking light problem and can't see any blown or faulty caps please re heat or re solder your FETs and main components may be there is cold solder or any lose connection
Thanks

[mbsqw1d]

Re: Samsung LCD Power Board turning on and off.

found that the T0-220 MosFET QB802 has a loose joint, solder has cracked on one of the pins. Hope a resolder will do the trick. else i wouldnt know what part id need to replace it?

UPDATE: Re-soldered the pin. TV has been working 100% since.

[thevolatile1]

Re: Samsung LCD Power Board turning on and off.

update... All other parts checked out ok from the list & don't you just hate looking for tiny numbers on pcbs.. or maybe my eyes are just getting old...
So this fix - just the 2 parts - QM801 FQPF5N50C mosfet & CP803 150uf @ 450v capacitor.

update.... this tv is still working fine with the mosfet & capacitor replacement.

[budm]

Re: Samsung LCD Power Board turning on and off.

Oooo, but they are 'EXTRA HEAVY DUTY'!

[JonathanAnon]

Re: Samsung LCD Power Board turning on and off.

It checked out fine when I tested it ... I tested it out of circuit first .. (i.e. the way it was in the photo above)..... The telly is coming back on now after soldering it..... I'm not sure what's going on, I'm gonna have to have a serious conversation with the chap....

At the very least I've sorted out the mystery of why his remote control doesnt work anyway



You just dont get the twenty years out of a set of batteries like you used to..

[jetadm123]

Re: Samsung LCD Power Board turning on and off.

Does that mosfet have a date code stamped on it? Compare the year of the mosfet to the manufacture date of the TV. If it's the original mosfet, then the year of manufacture should be the same (or very close) as the TV set.

[budm]

Re: Samsung LCD Power Board turning on and off.

I can tell it was worked on because the Green PCB masking is scratched up, it is not that easy to remove the green masking unless it was heated up and scraped by the soldering tip. By the way, does this transistor check out OK?

[JonathanAnon]

Re: Samsung LCD Power Board turning on and off.

It looks like some one had worked on this board and did not solder the part.

Hi again Bud, I did think that... cos the joints just look too clean, as if the chip was just screwed in to the heatsink and not actually resoldered... also the mess solder below the middle pin indicates that somebody was at it... but I know the guy that owns it and he says it's just started having problems and did not mention that he had anybody else looking at it.. ??

[budm]

Re: Samsung LCD Power Board turning on and off.

It looks like some one had worked on this board and did not solder the part.