Samsung Plasma PS50C687 3D No Picture only Sound - Need help -

[tomre]

I´ve got a defective Samsung Plasma TV PS50C687 with sound but no picture.

Findings:
After removing the back cover I found a green led on the logic board blinking every 5 seconds.
I´ve checked the power supply -stand alone- and found that all voltages seems to be okay (VSTBY and V5.3 about +5,26V, Vg=+15V, Va=+55V and Vs=+209V).

Next I´ve checked the Y-Main board, the Y-Buffer board and the X-Main board.
On the Y-Main board I found a lot of shorted transistors and on the Y-Buffer board I found a driver IC with shorts. On the X-Main board I didn´t found any shorted tranistors or blown components.

What I´ve done:
I´ve bought an new Y-Main, Y-Buffer and X-Main board.
Before I´ve replace the boards (at the same time) I´ve checked the new boards for shorts. But no shorts has been found.

But after switching the power on, I had the same problem as before: Sound but no picture and the led on the logic board blinks every 5 seconds.
The Vs and Va voltages comes only up for about 1,4 seconds.

I´ve checked the three new boards again for shorts but all transitors and drivers are okay.

But as soon as I disconnect the flat cable between the logic board and the Y-Main board, the Vs and Va voltages comes up steady and the green "heartbeat" led on the logic board blinks every second.
Now it´s also possible to adjust the Vsc voltage (-190V) on the Y-main board.

Does any one have an idea and can help me?

Thanks in advance, Tom

P.S.: Sorry for my bad english.

[Andrew F. Ali]

Re: Samsung Plasma PS50C687 3D No Picture only Sound - Need help -

Look on the Y-Main Bd. for test points marks Vsc + and Vsc - and a control marked Vsc Adj. Place the red probe of the DMM on the Vsc + and the black probe on the Vsc - and adjust the Vsc control to the required -190Vdc if necessary. However ther may be a problem wth the Logic Bd causing your problem.