Samsung PS51D8005 no picture

[PowerAmpFreak]

Hi all
Started as a routine mainboard change (no standby light or activity)
Powersupply tested on bench (OK)
Shorting the jumpers on logic to start test pattern mode.
Everything starts up (and sounds) alright.
The buzzing can actually tell when patterns change.
BUT there is one little thing missing - the picture itself.
Completely dark, nothing
Powerboards heats up as they should, PSU voltage within spec.
Candic camera?

[tom66]

Re: Samsung PS51D8005 no picture

Buzzing can be a cracked panel. Any panel glow? (Very low minimum luminance.)

[PowerAmpFreak]

Re: Samsung PS51D8005 no picture

The screen is really ALL black. Just checking.

Like some "enable" signal is missing...

[tom66]

Re: Samsung PS51D8005 no picture

Ok, Vs/Va ok? Control board LED flashing steadily?

[PowerAmpFreak]

Re: Samsung PS51D8005 no picture

Yes sir, VA and VS OK. Logic LED flashes about 1Hz.

According to owner, an old lady, it went dark during operation.
Not the one I could expect smashing the screen...

The heat spread is a little abnormal perhaps.
The Y-buffers goes hot quite immediately after power on. The same goes for all heatsinks but one on the Y-SUS. The X-main is all cold. (but buzzing qietly)

[tom66]

Re: Samsung PS51D8005 no picture

Check -Vsc, Ve and Vsch where available... also if you have a scope, check if X and Y are giving the correct waveforms on the output terminals. Check fuse for Va on E/F logic buffers.

[PowerAmpFreak]

Re: Samsung PS51D8005 no picture

I will check later today. But do you believe the logic could be faulty even if it's flashing the led?

[tom66]

Re: Samsung PS51D8005 no picture

I suppose it's possible but unlikely. The LED indicates it thinks the panel is working properly (being sustained, responding to discharge correctly, and no errors on SUS boards.)

[PowerAmpFreak]

Re: Samsung PS51D8005 no picture

Yes, it feels like a longshot.
The mainboard is appearently dead. It does not drive PS_ON low or high, does not respond to buttons or IR, and does not light up the standby led.
Wonder if the mainboard failure may be a secondary failure due to some Sus/Buffer/Logic kind of failure.

[tom66]

Re: Samsung PS51D8005 no picture

I can't see a sustain board causing a main board failure; they're too far disconnected.

[PowerAmpFreak]

Re: Samsung PS51D8005 no picture

I totally agree. That's why I am confused.

[tom66]

Re: Samsung PS51D8005 no picture

Well, if you have access to a scope, checking the sustain outputs will tell you if you have a sus, control or panel problem.

[PowerAmpFreak]

Re: Samsung PS51D8005 no picture

Yes, I will hook the scopes in and see what I get.

[PowerAmpFreak]

Re: Samsung PS51D8005 no picture

I think the devil himself moved into this Sammy.
Today when I fired it up, the PSU shut down directly. (A new day - a new behaviour)
Then I measured across the Y-buffers. 20ohms across the red caps...
Caps are ok.
Driver IC's?

[tom66]

Re: Samsung PS51D8005 no picture

4th IC on right looks like it has a hole in it.

Panel is DEFINITELY not cracked? If so, Y-buffer should fix it. But slightest crack (even right on the edge), that will fry the IC and it won't be fixable.

How to find bad IC:
https://www.youtube.com/watch?v=51SZsfH60EY

[PowerAmpFreak]

Re: Samsung PS51D8005 no picture

The 4th IC has some of the silicone splashed to it. It looks like a hole though.
But I begin more and more to believe the panel are bad.

Perhaps the main failure was bad mainboard. During transport the owner managed to crack the screen...

[tom66]

Re: Samsung PS51D8005 no picture

Well, bad Y-buffer on these will cause a black screen and the screen can still be OK. But, it is important to check the panel has not been cracked, causing the Y-buffer to fail.

[Kjelds]

Re: Samsung PS51D8005 no picture

Hello there!

As I'm totally new to this awesome community and therefore need to post a reply on thread before I can make my own thread, I thought I would do it in this one since I have what I think is the same initial problem with the same model.

So one evening I couldn't power on my TV. I didn't respond to anything. No red LED, no picture, no nothing. As I know a lot of these Samsung TVs have had problems with caps, I thought I would give it a go. I have a masters in electrical engineering, so I thought I would be able to fix a couple of bad caps However, I've never tried to repair anything like this before, so I would already now like to apologize for any stupid questions.

I removed the back cover of the TV and noticed the that the SMPS made a quite buzz. I also noticed that the only LED, located on the logic board, was off.
I've probed around with my multimeter and discovered that the logic board was supplied with power from the SMPS. I then thought the problem would be with the logic board.
However, I then stumbled upon this video: https://www.youtube.com/watch?v=JjrwTZC5nVg where they test the logic board. I did the sequence 2:45 in to the video, where they short circuit the PS ON to ground. Then when powering up the TV, the LED on the logic board turns on and starts blinking at with five seconds interval (I've made a small recording here: https://www.youtube.com/watch?v=E7IB_TXWeXI).

So now I think the problem is the Main Board. I went on to try to get the test pattern showing (guide at 3:10 in the video above). However nothing happens, just the same as with PS ON to ground. I would have thought this last test would have by-passed the main board some how, thereby confirming, that the issue might be somewhere else.

Any ideas would be greatly appreciated! The information shared on this community has already helped me tremendously. For example I was able to find a service manual for the TV in question, which before took me hours to no avail. So a huge thanks to you all already

[Kjelds]

Re: Samsung PS51D8005 no picture

Hi again,

Just wanted to give an update. Today I found out that during a previous check I disconnected the Y-sustain board . So I connected it to the SMPS again and KABLAM! test sequence is running on the screen!

Here's a little vid: https://www.youtube.com/watch?v=L7XzYaNIxfY

I guess that means, that the mainboard is the culprit, right?

If I'm right in the above, then I just need to get my hands on a mainboard. Any suggestions on where I can get this board? When I google it, they are all out of stock

[Kjelds]

Re: Samsung PS51D8005 no picture

Yet another update and sorry for spamming. Detached the mainboard from the TV and looked it over. Noticed that the area around the main processing unit is yellow/brownish (see attached picture). Is this normal, or is it an identification of a burned out processor?