Samsung PS50C91HD - No picture, not sure which board is faulty

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Ah ok. I found that tiny SMD fuse. I just tested it on the board and there is continuity. very low ohms. Do I have to desolder it to check properly?

That sounds fine.

Can you post a picture of the board? - There may be other components to check.

Come to think of it, I never thought to ask you to check the power supply output voltages (not just the sustain voltages.) I thought sound was good enough - but can you check the outputs going to the main board in case one of them is a bit low (okay for main board but not for logic board.) And if there's a separate supply cable going to the logic board, check that for a good 5V/12V or other voltage.

[edan]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Hi tom,

I'm getting 5.22V instead of 5.3V on the 6 cable connector from the PS board to the smaller logic board underneath

On the CN801 connector (ribbon cable going from PS board to logic main) I was getting very low voltages like 0.68V for the 12V and 5.3V lines, maybe because I was testing without it being plugged in?

Also by accident, I hot-plugged the CN801 connector back in without switching off power, hope I didn't damage anything.

I've attached a pic of the smaller logic board underneath as well.

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

5.22V is fine.*

(*probably.)

Hot plugging is only bad if you do it on the sustain boards, in which case that usually blows the fuse but everything else survives.

What is the voltage on either end of the fuse on the logic board?

I see several LEDs on the board, do these light? (One is marked LED2000.)

I've highlighted two devices that are probably voltage regulators. With the black probe grounded on the case and the TV turned on:

For the bottommost - check all 5 pins and report back.

For the topmost - check both exposed pins and the metal tab. Don't check the centre pin as that's the same as the tab (electrically common.) Report back the part #.

Be very careful not to bridge any pins while checking.

[uberplasma]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

what you don't speak Hungarian? lol
the new window comes up and look beside the preview and it will say "get manual" after a few secs, the other links go to other things. This manual is actually pretty good, it will show what connectors carry which voltages
Sorry reading some posts it seems that you said there was no 5V, was advising to trace from where you did not have the 5V to find the culprit, if no 5V anywhere to any board the problem is in the main power, but if you have it to a board trace the path to where you loose it on the board, schematics help so you don't have to handle the board while powered and can just probe on the component side rather than the foil side.
SMD fuses look like little white(usually, but there are different colors)rectangles, as well as little round cylinders, usually black with a rating on them.
it should measure very low ohms, isolate the board and check as well, might be reading a short somewhere else, again if there are multiple routes behind the fuse you may get a false reading, verify from schematics and the foil itself.

[nickdablack]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

I have a PS50Q91HD with exactly the same symptoms. I did have a bulging cap on the X-main board. I have replaced it but no improvement yet.

On point CN810 and CN809 on pin 1 (Vg) I am getting 14v. Is this correct? I cant find anywhere to say what the voltage should be.

[tw2005]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

I hate faults which don't have an ending so i'm tacking onto this one because all of the above applies to my PS50C91HD as well.

My symptoms are as follows.

1. Plug-in standby power available, front indication normal.

2. turn on either front button or remote, blinking front light then locks on solid.

3. From rear of TV (internal) power on LEDS illuminated on X-main, Y-main, CTRL Logic Board and Otic audio out on Main Board glows red.

4. voltages normal.

5. Nil display , but sound and controls normally.

6. No obvious signs of any blown chips,fets or capacitors.

7. Watching the activity LEDs as set is powered on I noticed there was an activity LED as well as the power on LED on the CTRL Logic board. This blinks at 1 sec intervals and quit suddenly after 10 secs or so.

8. With X-main disconnected, same result with the CTRL Logic LED, Connected X-main and Y-main then disconnected, activity LED just kept blinking.

So at this stage I was suspecting faulty Y-main and have quickly checked the FETS which I found an entire bank short cct (Q5500,5302,5303,5304,5306) 1 x 2SK2837 N Type FET, 4 x 80N30W N Type FET 80A, 300V. Q5303 was dead short and shorted the remaining FETs which tested ok once Q5303 was removed.

Thats where I'm at, fingers crossed it was just a protection cct shutdown of the screen.

I could not find a 80N30W TO3P so I'm throwing in an 80N30P in the TO-264 package.

If anyone has an opinion on this I'd like to hear it. I'm assuming the main difference between the 2 would be thermal dissapation and maybe the TO-264 may not be as durable?

I'll post up the results once i have the new FET, hopefully it'll arrive tomorrow.

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Ah ok. I found that tiny SMD fuse. I just tested it on the board and there is continuity. very low ohms. Do I have to desolder it to check properly?

Nope that should be fine... Can you check the voltage on both ends of the fuse, relative to the metal frame of the TV? It will either be 5V or 12V, I think.

[tw2005]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

,

[tw2005]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Nope that should be fine... Can you check the voltage on both ends of the fuse, relative to the metal frame of the TV? It will either be 5V or 12V, I think.

?? I'm confused

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

?? I'm confused

I'm being silly, I was reading only the first page.

[tw2005]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

I'm being silly, I was reading only the first page.

Yep, I thought it was a slip up. Usually your replies are logical and well thought out. It did not match up with my blurb.

[scokljat]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Maybe it's time to test all Y and Z/X board components under heatsinks for shorts/open. FET's, diodes, transistors. If Vs and Va is correct and fuses are intact I believe FET's on input stage are not shorted. I would inspect FET's on YSUS output stage that go to Y buffers. Also, check the buffer boards for shorts. This particular scan IC's are as I learned on this forum prone to failures and they like to kill YSUS as well. There is great info of how to test FET's and buffer shorts on this forum and coppeltv. All you need is standard multimeter.
Another thing, as I understand, TV goes to standby ok, powers up ok, changes programs/video inputs, sound is ok. You should try a HDMI source (which in addition imply complex audio video processing and D/A conversion) and if it also produces normal sound than I beleive main video board and most circuitry on it is ok.


Cheers!

Suad

[psmedley]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

I could not find a 80N30W TO3P so I'm throwing in an 80N30P in the TO-264 package.

I've ordered a ysus repair kit for my Sammy 50" - I had several blown mosfets, however a couple of the 88N30W's seem ok - not shorted at least. If you want one - message me your snail mail address and I'll thrown one in the post for you.

[tw2005]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

I've ordered a ysus repair kit for my Sammy 50" - I had several blown mosfets, however a couple of the 88N30W's seem ok - not shorted at least. If you want one - message me your snail mail address and I'll thrown one in the post for you.

Gee thanks, obviously i'll be paying you for them. At this stage I'm good.

I should have waited a bit before ordering but RS was overnight.

Updating where I'm at, I'ved replaced the dead FET.

Power on, same result. Obviously at this stage I'm thinking it must have done something to and I did not check the buffers but thinking a bad buffer took out the FET I removed the upper first.

Turned on and saw the screen flash. I have a PS50Q7 which is just the generation before so its buffers are physically the same with slight component changes. I believ they are interchangeable so I threw in the top from that.

Powered up and have full picture however it's ok but not very good quality and seems very noisy and speckly.

I changed the bottom with the other model and no improvement.

I've checked the panel voltages and set them to spec, no great change either.

So now I'm in need of an experience plasma person to help me out on what direction to take because the boards are just to expensive to keep guessing.

I'm thinking I should get some buffers but I don't expect that alone to fix any thing.

Do i still have y-main issues with other components or should I be looking at the X-main?

The PS50Q7 is suppose to have intermittent black screen and intermittent half black screen issues but I have not it on long enough for it to fail.

Currently it has a perfect picture which in comparison to the 50C91 I say exceptional.

[heckeng]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Looks like there's a lot of these TVs which are faulty. I'm chasing the same problem(s)
Have replaced VIPer22 on power board & 2 STTH20P03S on the Ymain board. Anybody got a circuit diagram / service manual?

[tw2005]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

This is all I have for the PS50C91HD

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Have manual for PS50Q91HX... may be close enough.

http://www.tgohome.com/ServiceManual...h=Submit+Query

[heckeng]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Couldn't download that file from tgohome? Said file is corrupted? Checked the other pdfs & they were OK.

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

I see the problem, give me a few moments to try and find another copy and re upload it. It probably got corrupted on upload.

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Here it is, re-uploaded:

http://www.tgohome.com/ServiceManual...1HX_PS50Q91HX_[SM].pdf