Samsung PS42D4S picture dies

[thefox100]

Hi all. Picked up this Samsung for repairs recently. Initially suspected the Y Sus or buffers as I was told it had audio but no picture. On inspection there is a good picture and sound but after about 5 mins the picture breaks up and disappears leaving a black screen and just the audio. If I turn off for an hour or so and then back on again, the picture returns as normal for around 5 mins again.

I can't see any bad caps anywhere, so where would I start with this? Dry joints somewhere maybe?

Perhaps a red herring, but the last time I tested this, I turned Picture Mode to Normal (from Dynamic) and DNIe to Off - the picture stayed on for an hour before I turned the set off. Could these settings have an effect on how long the picture stays on - if so, what board/components are being affected by those settings?

Thanks in advance.

[thefox100]

Re: Samsung PS42D4S picture dies

Some pics.

[ATTACH]Layout[/ATTACH] [ATTACH]Ysus[/ATTACH] [ATTACH]Power Supply[/ATTACH] [ATTACH]Inputs[/ATTACH] [ATTACH]Xsus[/ATTACH]

[thefox100]

Re: Samsung PS42D4S picture dies

Update:

Removed all boards and checked for heat damage, dry joints and burnt/blown/bulging components. All looks ok. Cleaned all ribbon connections too.
With Picture Mode still in Normal a DVD via S-Video played for an hour before the picture started breaking up again. It will stay on, but is juddering and jumping around together with the horizontal 'bleed' lines as seen in the attachments.

Voltages at startup are: Va = 71 (label says 70); Vs = 176 (label says 175); Ve = 165 (label says 165); Vset = 175 (label says 173).

Any ideas anyone?

[thefox100]

Re: Samsung PS42D4S picture dies

Further Update:

Had it running again today with a Digital Meter attached to the voltages on the power board, one by one. As the fault appeared again, none of the voltages varied. Each time the fault appears, I switch off the mains supply for about 10 seconds, then back on and it will run for another hour or so!

Does anyone have any ideas or hypothesis as to what could cause this type of picture distortion?

[victor_cj]

Re: Samsung PS42D4S picture dies

Bad soldering at X-main, Y-main, SMPS module. Check for cracked soldering, cleean the surface to see them. The optocouplers can create the same problem.

[thefox100]

Re: Samsung PS42D4S picture dies

Thanks victor - makes sense. Will go over the boards again tomorrow in daylight.

[thefox100]

Re: Samsung PS42D4S picture dies

SOLVED.

A good clean of all the boards, cleaning and reseating all leads and connectors, renewing heatsink paste seems to have fixed the problem. I'm leaning towards the problem being with dried out heatsink paste on various components.

An old telly, I know - but good for the spare room - and free!

Great forum and I hope this solution helps others.