Samsung PS42A410 has sound but no picture

[nick1969]

Hi,

I have a 42" Samsung plasma model is PS42a410 it has working sound but nothing on screen, when i power it up it does everything normal and the LED inside on the control board flashes
The screen is completely dark no change when turned on
I have a working 50" that i tried the PSU and Main AV board from but that didnt make any difference
Any help greatly appreciated!
Thanks

[tom66]

Re: Samsung PS42A410 has sound but no picture

If you connect a source, can you hear any sound?

[nick1969]

Re: Samsung PS42A410 has sound but no picture

i will try a source, with the antenna connected i hear sound from the Local channels

[tom66]

Re: Samsung PS42A410 has sound but no picture

That's good enough to show the main board is probably working, so we'd be looking at a Y-main or X-main failure. Most likely Y-main.

[nick1969]

Re: Samsung PS42A410 has sound but no picture

Is there some way of checking each to know what's failed?
Thanks for your help

[tom66]

Re: Samsung PS42A410 has sound but no picture

Usually there is. Can you post pictures of the boards inside your set?

[nick1969]

Re: Samsung PS42A410 has sound but no picture

Is this ok or do you prefer individual shots?

[tom66]

Re: Samsung PS42A410 has sound but no picture

Ideally a closer shot of each large board in the set as we need to see the smaller components and get an idea of the design/layout used.

[nick1969]

Re: Samsung PS42A410 has sound but no picture

Is this OK ?

[nick1969]

Re: Samsung PS42A410 has sound but no picture

Just to recap, i swapped the only 2 boards from a 50" that were the same with no difference The main AV board (3rd picture) and the PSU (last picture)
The Screen is black and no glowing or flickering when powered on, only sound
Thank you

[tom66]

Re: Samsung PS42A410 has sound but no picture

I've highlighted two fuses on the Y-main. Please measure the voltage on both ends. Highest DC range (more than 200V). Red probe on one end of fuse, black on chassis, swap to other end, repeat for both fuses. Set should be switched on with audio playback. Be careful not to touch any part of power supply while set is switched on due to shock hazard.

[nick1969]

Re: Samsung PS42A410 has sound but no picture

Ok ....
The top small green fuse has 14.8v either side and the bottom glass one has 208.2v either end

[tom66]

Re: Samsung PS42A410 has sound but no picture

Those are both good readings.

Next, test the voltage across this capacitor I have highlighted: red probe on one end, black probe on the other end. It does not matter which way around.

This is one cap in the ERC cap bank. Functioning voltage is around 60 to 120V DC.

[nick1969]

Re: Samsung PS42A410 has sound but no picture

I have 97.5v across that cap

[tom66]

Re: Samsung PS42A410 has sound but no picture

OK, well, it appears that you should have a glowing screen! But in a dark room would you say there is no visible difference in brightness between the TV being on and off?

[nick1969]

Re: Samsung PS42A410 has sound but no picture

Hi again,
Just powered it up in a dark room and nothing at all not even the slightest glow whatsoever

[tom66]

Re: Samsung PS42A410 has sound but no picture

On the Y-main can you see any points marked VSCAN or VSC?

[nick1969]

Re: Samsung PS42A410 has sound but no picture

I see VSCH and VSCAN

[tom66]

Re: Samsung PS42A410 has sound but no picture

Can you measure the voltage at VSCAN? Put red probe on the test point and black probe on the chassis. 200V DC range. VSCAN/VSC is usually written on the panel sticker to refer against.

[nick1969]

Re: Samsung PS42A410 has sound but no picture

VSCAN is showing 0 volts
VSCH bouncing between 42v and 48v