Samsung 55KS8005TXXE power cycling

[baldharry]

Hello!

My second TV to fix, first one was a success So the problem with this one is the power cycling. At first I did the led test, plug out MB (mainboard) and plug the powercable. Backlights turn on and TV stays on.

At the moment MB is plugged in, standbylight turns on, TV turns off for a couple of seconds and then tries to start. Backlight flashes bright, dims out and TV turns off while PSU is having a faint ticking or clicking noise. TV stays off for a couple of seconds and tries to start again. This power cycle happens for as long powercable is plugged.

I disconnected everything else except IR-cable from MB, same behaviour. This made me think problem lies in the MB and ordered a new one. But the new MB did not make a difference. Same behaviour. So I think the problem is after all in the PSU.

Capacitors are tested and are OK. I took voltages which are fine with MB unplugged. Attached is a picture with voltages in three different states. PSU has a jumper wire where standby is supposed to be measured, saying it should be 7.5V and at power on it goes up to 11.8V. When measured they are 8,9V and at power on 12,84V. Is it supposed to be like that?

Otherwise, voltages seem ok when MB is unplugged. Even in standby they seem about right? But at power on, things go weird. Voltages drop to a certain point at power off and rise again at power on. I'm baffled, please help!

Thanks in advance.

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

with tv unplugged from power which it should be any time connecting cables, unhook one at a time of the wide flat cables and try tv, so youre trying it with one cable unhooked then plug it back in and try it with other cable unhooked.

[Storyteller12]

Re: Samsung 55KS8005TXXE power cycling

with tv unplugged from power which it should be any time connecting cables, unhook one at a time of the wide flat cables and try tv, so youre trying it with one cable unhooked then plug it back in and try it with other cable unhooked.

+1

[baldharry]

Re: Samsung 55KS8005TXXE power cycling

with tv unplugged from power which it should be any time connecting cables, unhook one at a time of the wide flat cables and try tv, so youre trying it with one cable unhooked then plug it back in and try it with other cable unhooked.

Argh, forgot to write that in the first post. Tried with only one cable at the time, no difference. Tried with both off, no difference

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

ok, thats probably a good thing, probably no panel damage.

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

I kind of suspect that its a mainboard issue, try the hairdryer test, with everything plugged in heat up the electrolytic caps on POWERBOARD for a couple minutes then try the tv, don't wait til it cools off, try it while its still hot but your powerboard looks good to me.

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

does the place where you got the mainboard have another they can send you if you send that one back? but don't pay twice, if they do have another available, send one back and they should send the other out.

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

do try it with the panel button cable unhooked, the one with volume channel up down etc, sometimes they go bad and are to blame for the cycling.

[baldharry]

Re: Samsung 55KS8005TXXE power cycling

I kind of suspect that its a mainboard issue, try the hairdryer test, with everything plugged in heat up the electrolytic caps on POWERBOARD for a couple minutes then try the tv, don't wait til it cools off, try it while its still hot but your powerboard looks good to me.

Ok, heated with hairdryer but the capacitors don't feel that hot, can easily hold finger on them without burning. Same effect. Heated for about 3-4 minutes.

does the place where you got the mainboard have another they can send you if you send that one back? but don't pay twice, if they do have another available, send one back and they should send the other out.

The seller (Aliexpress) said the boards are tested. Getting a new one takes about 4 weeks to arrive.

do try it with the panel button cable unhooked, the one with volume channel up down etc, sometimes they go bad and are to blame for the cycling.

It has only power button. Disconnected but cannot power it up so TV stays in standby now

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

ah ok, so this one has only power button and has to be operated with remote.

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

I see, sometimes the boards can get damaged in transit, did it arrive in a anti-static bag?

[baldharry]

Re: Samsung 55KS8005TXXE power cycling

I see, sometimes the boards can get damaged in transit, did it arrive in a anti-static bag?

Errm, can't remember. Any ideas how to test it?

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

and you're sure that the replacement board is a match? usually you need to match the alphanumeric digits on a sticker on the board, not sure if the one in the picture has one, I just see the QR deally.

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

and you tried it with the wifi board unhooked?

[Storyteller12]

Re: Samsung 55KS8005TXXE power cycling

Disconnect both lvds cables going to the panel and try to power on. See if the backlights stay on or if you can hear anything on the speakers.

[baldharry]

Re: Samsung 55KS8005TXXE power cycling

and you're sure that the replacement board is a match? usually you need to match the alphanumeric digits on a sticker on the board, not sure if the one in the picture has one, I just see the QR deally.

Yes, by sticker number on chassis and labels on mainboard. Seller wanted pics of the original board to use for comparing. Seller had compared some resistors and capacitors different places on the board.

and you tried it with the wifi board unhooked?

As written in first post, disconnected everything except IR-cable. Also tried disconnecting only one of them in order.

Disconnect both lvds cables going to the panel and try to power on. See if the backlights stay on or if you can hear anything on the speakers.

Did this a couple of posts above. No difference. Backlights stay on ONLY when mainboard is unplugged

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

well if the cable from powerboard to mainboard is ok, then it must be the mainboard at fault.

[baldharry]

Re: Samsung 55KS8005TXXE power cycling

well if the cable from powerboard to mainboard is ok, then it must be the mainboard at fault.

Yeah the cable is tested with continuity and seems ok.
Oh crap, but how can they both be broken the same way? Any clues where to start "debugging" the mainboard?

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

its tough, here's a little of what Tampatac went thru, I can't see if he made another video on this tv or not, last thing he says I think, is that he's going to try to fix the mainboard but I don't see the next video, he may have gave up, not sure: https://www.youtube.com/watch?v=-_e9DFeZYKI

[nomoresonys]

Re: Samsung 55KS8005TXXE power cycling

Diah or Lotus might have a better idea on whats wrong, mainboards are not an easy tackle.