Samsung PN51D450A2DXZA - No Video

[mattress]

Hello everyone!

This is my first time ever messing with a plasma.
I was given this 51" Plasma from a friend that was going to junk it.

Initial inspection: TV would attempt to power up with audible power up jingle sound, and nothing. Screen would never light up.

Pulled the back off. Observed slow "heart beat" led. 5 seconds on, 2 seconds off.

Found a fast-track troubleshooting PDF file.


Measured resistance between VS testpoint and ground, found it was shorted.

Disconnected X-main. Short was gone. concluded X-main was bad. Could not identify bad component on board; probably bad mosfet.

Received replacement X-main board in mail today. Installed and tested for short between VS and ground, and found none!

VS, VA, VSCAN, and VE all measure correct voltages for a split second after power-on before falling back down to zero. Power on still plays the audible jingle. Heartbeat still slow. 5 on, 2 off.

I attempted shorting PS-ON to ground, and attaching a jumper to pin 3&4 on logic board, and applying power. Screen lights up and flashes what appears to be white snow for just a flash before powering down again.

I'm assuming the powersupply is sensing a short, and shutting itself down for protection, or it is not sensing Xmain or Ymain and shutting down. It will not run with Xmain or Ymain disconnected.

Not sure where to go from here.

[capkid]

Re: Samsung PN51D450A2DXZA - No Video

This may be helpful: https://www.badcaps.net/forum/showpo...3&postcount=13

Additionally, check for shorts in the transistors on the Y and X heat sinks.

Tom's buffer test: http://youtu.be/51SZsfH60EY

[mattress]

Re: Samsung PN51D450A2DXZA - No Video

Did the y-buffer test, and checked ok. Love norcal's videos! Will check on that tomorrow afternoon.

To check for shorts, do I just probe between all the transistor legs and the heat sink?

Thank you for the tips.

[capkid]

Re: Samsung PN51D450A2DXZA - No Video

Did the y-buffer test, and checked ok. Love norcal's videos! Will check on that tomorrow afternoon.

To check for shorts, do I just probe between all the transistor legs and the heat sink?

Thank you for the tips.

You probe between combinations of legs. Perform the test with the meter in diode mode. Example:

Test 1a: pin 1 - neg probe, pin 2 - pos probe
Test 1b: pin 1 - pos probe, pin 2 - neg probe

Three-legged components will mean more combinations. If you see 0.00 on your meter, you have a short. You may have to de-solder a component's legs from the board if the readings seem inconclusive.

[mattress]

Re: Samsung PN51D450A2DXZA - No Video

Main power board

DS825 pins 1 & 3 beep both ways
DS824 pins 1 & 3 beep both ways
DS801 pins 1 & 3 beep both ways
DP802 pins 1 & 3 beep both ways
(Beep = 0.0)

QS801 weird buzz pins 1 & 3 - 20ohms
QS802 weird buzz pins 1 & 3 - 20ohms

Ymain seems ok. Xmain all ok.

Main power board and ymain have a few that have white caulking around the legs, and I won't be able to check without removing the boards and probing from the back side.

[mattress]

Re: Samsung PN51D450A2DXZA - No Video

47 ohms between SVC_OUTH and SVC_OUTL on ybuffer both ways

[mattress]

Re: Samsung PN51D450A2DXZA - No Video

Ymain board is significantly darker around D5000 area

[capkid]

Re: Samsung PN51D450A2DXZA - No Video

The info you've posted isn't very useful without pics.

[mattress]

Re: Samsung PN51D450A2DXZA - No Video

I will try to do my best!

Here are a couple of quick shots displaying the back of the panel with all the boards, a shot of the main power supply in the frame, and then a close up of each component I posted earlier. Also, I included video clips of what the screen shows when I try to jump it into test mode

I hope this helps, and I really appreciate you taking the time to check this stuff out with me! Thank you so much!

https://www.dropbox.com/s/w55povrpbr...mages.zip?dl=0

[capkid]

Re: Samsung PN51D450A2DXZA - No Video

Your power supply is most likely fine. To test the X-main and Y-main components on the heat sinks, you need to remove the boards from the TV. It's possible that a bad Y-main could short out your replacement X-main, since they're chained. So, I would avoid powering up the TV until you've performed the Y-main and X-main component checks.

[mattress]

Re: Samsung PN51D450A2DXZA - No Video

I'm still in the learning phase of all this.

I couldn't really figure anything pertinent out by testing the components.

I replaced the Y-main board, and still have the same issue.


I powered the tv up with y-buffer disconnected from panel, same result.
I powered up tv with y -buffer disconnected from y-main, got same result.

Installed replacement y-main, with y-buffer disconnected, same result.
Connected y main, disconnected panel, same result.
Connected panel and y buffer to new y main, same result.

Have replaced y and x mains. Don't know where to go from here.

[mattress]

Re: Samsung PN51D450A2DXZA - No Video

Also it appears I was a little too hasty in my y-buffer test. I found 2 pins that are shorted:

https://www.dropbox.com/s/joexv2e5g3...%20PM.jpg?dl=0

https://www.dropbox.com/s/eqhhzvg4tj...%20PM.jpg?dl=0

https://www.dropbox.com/s/ya7vzedql7...%20PM.jpg?dl=0

https://www.dropbox.com/s/473bkn19ix...%20PM.jpg?dl=0


I guess that means I need to replace y-buffer??

[mattress]

Re: Samsung PN51D450A2DXZA - No Video

Received replacement y buffer. Tested it before installing. Tests worse than the original

[mattress]

Re: Samsung PN51D450A2DXZA - No Video

Received second y buffer today. Also tests positive for grounded chip. Ugh.

[mattress]

Re: Samsung PN51D450A2DXZA - No Video

Ok. Finally have some promising news.

I finally received a y-buffer that didn't come pre-shorted (thanks to shopjimmy!)

Now, I have a vertical black column in the middle of the screen, with the very middle 1px column sparkly white pixels.

Also what appears to be a 1 px row of black pixels near the bottom.

Results persist through test-pattern mode.

Also notice noise coming from, or from around, the y-sustain board.



https://www.dropbox.com/s/hmai0dqnp8...%2058%20PM.jpg

https://www.dropbox.com/s/atij76jnjs...%2009%20PM.jpg

https://www.dropbox.com/s/kp6bbhhcg0...%2020%20PM.jpg



Should I create a new thread, or continue this one?

[MagicSmoke]

Re: Samsung PN51D450A2DXZA - No Video

That black bar looks like mine did. Unfortunately I think the panel is bad. The ribbon tabs at the bottom buffers have chips on them that fail from heat/bad design.

[johns1mj]

Re: Samsung PN51D450A2DXZA - No Video

The horizontal black line could be from a bad connection at the y buffer. Most likely the lower ribbon not in all the way. The vertical line looks like a bad connection at the boards at the bottom on the screen. I believe their called something like logic or input buffer boards. They are usually a pain to get to but I have fixed 3 tvs with similar issues just by resetting the connection. One tv was a bad connection to the screen and that means the panel is bad.