Samsung LE37A656 - half a picture for half an hour

[noahf]

When first switching on, the left half of the screen is black. Over the next half hour it changes to vertical stripes, then flickering. Even after an hour, the left half shows occasional artefacts. The behaviour is sensitive to mechanical shock. A judicious 'thump' on the top right area of the bezel can change the patterning and occasionally will clear all flickering. After a couple of hours, the picture is stable. Switching off, and then on again after 10 minutes causes the flickering to restart.

I have opened it up and have tried nudging each connector and each wire in each harness and cable, flexing each PCB, local cooling (spray), without any clear result. I have removed and cleaned every visible connector. I have replaced the T-CON board.

Any suggestions?

Thanks!

[Dgtech]

Re: Samsung LE37A656 - half a picture for half an hour

Something may be overheating

[budm]

Re: Samsung LE37A656 - half a picture for half an hour

It may have problem with the TFT driver ICs over heating, they are mounted on the flexible PCB between the long rigid pcb and the LCD glass panel.

[noahf]

Re: Samsung LE37A656 - half a picture for half an hour

Thanks for the quick response! However, I doubt that overheating could be the cause. The problem is worst when cold. After 30-60 minutes operation we get a normal (full) picture with no artefacts.

[tom66]

Re: Samsung LE37A656 - half a picture for half an hour

This is almost certainly a tab bond issue as Budm described. It is less overheating and more when the temperature hits an acceptable level the TV can work because everything is making good contact due to thermal expansion.
It's extremely common on Samsung TVs although I believe your set has an AUO panel it does happen with some AUO panels too.

[noahf]

Re: Samsung LE37A656 - half a picture for half an hour

Tom66 -- excellent! Well, more objectively, your diagnosis aligns with my own feelings that the culprit is a cracked solder joint and thermal contraction/expansion. Now, my question is what's the minimum replaceable unit? Is this flexible PC removable and available, or is it permanently bonded to the LCD panel? Anyone know?

[tom66]

Re: Samsung LE37A656 - half a picture for half an hour

Bonded to the LCD panel.

A temporary (sometimes permanent) fix is to apply a "shim" to the tab bond to hold it in place. This will apply pressure to the tab IC or tab bond, preventing the issue from occurring.

However, it doesn't always work, and isn't always permanent.

[truep]

Re: Samsung LE37A656 - half a picture for half an hour

Use heat transfer pads to shim the tab bonds.

[budm]

Re: Samsung LE37A656 - half a picture for half an hour

Examples:
https://www.badcaps.net/forum/showth...LN52A530P1FXZA

https://www.badcaps.net/forum/showthread.php?t=37887

https://www.badcaps.net/forum/showthread.php?t=37885

[noahf]

Re: Samsung LE37A656 - half a picture for half an hour

There is a PCB assembly mounted on the upper rear of the LCD panel under a metal cover. It is connected to the T-CON board by two wire bundles. It is also connected by two ribbon cables to two long, thin PCB assemblies mounted on the top edge of the LCD panel. Each of these, in turn is connected to the LCD by four flexible printed circuits mentioned by Budm. (Sorry, I couldn't find the official name for each of these PCAs.)

So I removed, cleaned and reinserted the ribbon cables at both ends and used electrical insulating tape to apply pressure to the flexible PCs and to the long thin PCAs. The only visible hint was on one of the ribbon cables, where a few of the tracks had degraded at one end. Anyway, for now the TV picture is good as soon as I switch on! No way of knowing how long this will last, but it's satisfying finally to have traced the source.

Thanks for all your help!