Samsung PN50A400C2DXZA no video

[kevinm34232]

The TV powers on normally and the screen glows, but there is no picture. I disconnected the LVDS cable and jumped pins 3 and 4 on the logic board. Turned the TV on and still nothing. I bought another logic board and same issue. Am I doing this procedure correctly, or what else could be wrong??

[tom66]

Re: Samsung PN50A400C2DXZA no video

Check the Va supply to the C-buffer boards, running along the bottom of the panel, if it goes missing this can cause a problem. NOTE: Do not re-plug Va connector with power applied or panel will be killed.

[kevinm34232]

Re: Samsung PN50A400C2DXZA no video

Thanks Tom, I was looking for where to check the Va voltage and saw this SMD fuse which is open. Thoughts?

[kevinm34232]

Re: Samsung PN50A400C2DXZA no video

I have 56V on the bottom of the fuse which matches the panel sticker for Va, and 9V on the top side. (That 9V is there even with the TV unplugged, and is not showing a short to ground on that side)

[tom66]

Re: Samsung PN50A400C2DXZA no video

Sometimes the fuses just fail with no obvious cause, try replacing it. If it blows again, the panel is probably shorting it, which would make the set scrap, this is rare though.

[kevinm34232]

Re: Samsung PN50A400C2DXZA no video

I replaced the fuse on the C-Buffer and it opened again. Could this be anything else but the panel?

[kevinm34232]

Re: Samsung PN50A400C2DXZA no video

Tom before I classify this one as a bad panel and junk, I just wanted to see if you thought it could be anything else?

[tom66]

Re: Samsung PN50A400C2DXZA no video

Could be a shorted ceramic cap on the E/F boards. Or a bad panel. Panel faults are common on this model. Can you remove the address driver connections (the ones connecting to E/F buffer) - or are they soldered to the board?

[kevinm34232]

Re: Samsung PN50A400C2DXZA no video

Do you mean the ribbon cables from the logic board to the lower buffer?

[tom66]

Re: Samsung PN50A400C2DXZA no video

No -- the cables from the lower buffer to the actual panel.

[kevinm34232]

Re: Samsung PN50A400C2DXZA no video

Ya the buffers are bonded to the panel.

[kevinm34232]

Re: Samsung PN50A400C2DXZA no video

I disconnected the F buffer from logic board and E buffer, and replaced fuse. Fuse didn't blow and I get test patterns on left side of screen.

[kevinm34232]

Re: Samsung PN50A400C2DXZA no video

Wait now I reconnected F-Buffer and turned on and the whole screen is working, weird.

[tom66]

Re: Samsung PN50A400C2DXZA no video

Could be an intermittent shorted capacitor... maybe try some freeze spray?