Samsung PS50C7705 clicks and clicks

[PowerAmpFreak]

Time for a new Samsung problem.
This time it's a PS50C7705 a superthin 3D plasma.
Problem is that when VA and VS has come up to correct operation voltages, it shuts down. So it detects some failure.
The PS ON signal from mainboard is in sync with the turn on/turn off sequence.
I have tried to disconnect Y-MAIN and then X-MAIN, but I think this set detects this so it's not useable in this set.
Measured across the Y-MAIN and X-MAIN without finding any shorts, etc
Buffers seems OK (no exploded IC's and not low resistance across decoupling caps)
I assume the powersupply is OK.
Please check the attached pictures.

[tom66]

Re: Samsung PS50C7705 clicks and clicks

This guide is for a similar plasma


In particular the test pattern jump may be of use, if you can pull VSON and PSON to the correct levels (PSON low, VSON high.)

[PowerAmpFreak]

Re: Samsung PS50C7705 clicks and clicks

I don't know if it's safe to force operate VS and PSU.
I remember my own PS42C455 plasma which gave me some gray hair. This had a shorted SMD cap on Y-buffer board. And it did exactly the same endless startup sequence.
Is it safe to operate the Y-MAIN without connected Y-buffers boards?

[tom66]

Re: Samsung PS50C7705 clicks and clicks

Yes, it is safe to operate without the buffers, but I would not immediately be expecting those as a fault. I would be thinking more of a main board issue. I recommend following the test pattern instructions.

[PowerAmpFreak]

Re: Samsung PS50C7705 clicks and clicks

Looking at the buffers I can see one suspect buffer IC with a small burnmark.
It's very small so can't be 100% sure if this is a burnet IC or not.
When operating without buffer board connected, the set behaves just as before. Clicks and clicks.
Maybe it senses the absense of buffer board and refuse to start
There are not low resistance across the buffer supplies either.

Finally, the screen flashes white for some milliseconds each time it tries to start

EDIT: Now tried putting logic board in testmode and jumpstart PSU. Then PSU stays on and screen looks "like it's ON without any picture signal" - can't see any problem with lines or so, I guess this means the power boards are OK and problem lies in the *damn* mainboard, ONCE AGAIN

[tom66]

Re: Samsung PS50C7705 clicks and clicks

But you should have had test patterrns if the main was bad. Check Va on X-buffers.

[PowerAmpFreak]

Re: Samsung PS50C7705 clicks and clicks

I have the test patterns!!
I was not waiting long enough for the first "gray" screen went out.

[tom66]

Re: Samsung PS50C7705 clicks and clicks

Oh, OK then -- definitely main board. Try EEPROM reset
http://wiki.samygo.tv/index.php5/UnB...y_EEPROM_Reset

[PowerAmpFreak]

Re: Samsung PS50C7705 clicks and clicks

No success in trying to reset the mainboard...
Also tried the EEPROM "jumper" reset, but it seems the mainboard is stuck in a loop.
What is strange is that standby led is continously on red, not flashing, like it should during power on.
Anyone else hating samsung mainboards?

[tom66]

Re: Samsung PS50C7705 clicks and clicks

Actually TBH I've never had a bad main board, except maybe for one old one, but I never was certain that it was the main board. That being said I don't work so much on their premium TVs. I had an LE40B652 power cycling - anyone in their right mind would have called main board but it turned out to be a shorted t-con.

[PowerAmpFreak]

Re: Samsung PS50C7705 clicks and clicks

Two bad Samsung mainboards in one week.