PS50C550 sound but no picture.

[niblettr]

Hi, just bought this faulty tv and would like some pointers.
With everything plugged in VS and VA measure correctly for about a second and decays to 0.

If i disconnect the LVDS cable from TCON to Ysus, voltages are correct and stay correct.

If I just isolate Y buffer and Zsus, voltage stay correct until I plug in the LVDIS cable.

Is this a Ysus board fault.

[sordids999]

Re: PS50C550 sound but no picture.

Posting pictures of the back of your tv showing the boards with clear pictures may help you more with fixing your problem

[niblettr]

Re: PS50C550 sound but no picture.

yeah, sorry. see attached. Its a Samsung.

[niblettr]

Re: PS50C550 sound but no picture.

On powering up, Vs reaches 210V, Va reaches 55v then drops quickly back down to 0.
If I disconnect the ribbon cable from Tcon to Ysus and cycle the power to the panel, VS stays at 210V, Va stays at 55V. Vsc also measures -199V.
when in the error condition, one of the leds on the Tcon boards flashes every 4 seconds. With ribbon cable disconnected (tcon to Ysus) voltages stay steady, the other led flashes instead once a second (good condition?)

I isolated two of the error lines on the ribbon cable by removing to 2 0407 resistors on the Tcon board and now with everything plugged in, all voltage stay up and led flashes once a second.

I think the tv is now in a state where more debugging can be done but don't quite know what to look for?????
I get quite high voltages between Ysus and the buffer board. Buffer board was measured for shorts but not found any.

What voltage should I be seeing on the ribbon cable of the Zsus board to plasma panel?

On the Ysus on the far left heatsink, there is are 3 T0220 devices, an ultra fast recovery diode feeding to Fets that are in parallel. On the anode of the diode there is -210V, the cathode side reads nothing as do the source and drain of the fets. I think there was 3v on the gates (going from memory, will check and edit this if I'm incorrect..)

[niblettr]

Re: PS50C550 sound but no picture.

Also, how does one bring up the test pattern? I have another Samsung tv that kinda works (vertical lines which there is nothing you can do about it.) and I tried every combination of jumper settings on the Tcon board but cant get the test pattern with LVDS cable disconnected.

[niblettr]

Re: PS50C550 sound but no picture.

Anyone? Ok, I managed to get test pattern on another samsung. (It worked all along I just didnt wait long enough for it to kick in.)

Could I rule out to Zsus by removing it and shorting the wide ribbons of the plasma (right hand side) to the chassis.) Or is that a bad idea? I just need to get the SOME picture up before I rule the plasma panel as being defective.

[Hamie]

Re: PS50C550 sound but no picture.

did you get test patterns on this TV?

[niblettr]

Re: PS50C550 sound but no picture.

nope

[Hamie]

Re: PS50C550 sound but no picture.

I'd jump the power supply on without the mainboard connected.
Then try test patterns again.

[Hamie]

Re: PS50C550 sound but no picture.

I can't see the legend table in your pictures on the power supply.

Usually it would need jumped:
ps-on to ground.
and
vs-on to 5v stand by.

[niblettr]

Re: PS50C550 sound but no picture.

Ok, will give a shot.
See attached, is that what you mean?

[Alastair E]

Re: PS50C550 sound but no picture.

There's a problem with the Y-SUS or Buffers.

Cable from Control-Board (No 'T-Con' on a PLASMA) Isnt called LVDS. Its just a cable. LVDS goes from M.B. to Cont board.

[niblettr]

Re: PS50C550 sound but no picture.

I'd jump the power supply on without the mainboard connected.
Then try test patterns again.

Tried but still same result.
I put the resistors back on the control board and the unit powers up with fault detected as before.

The fault obviously lies on the Ysus because I get that same condition with everything else unplugged.

Tried tracing the fault line on the board to see what drives it but its very confusing at the moment.

Also, there is a transformer on the Ysus that gets very hot but voltages that it is producing look good (i think) -ve large value?

[niblettr]

Re: PS50C550 sound but no picture.

In the attached is the transformer I mean. Also you can see on the opposite side of the board you will notice localises heating around one of the diodes near the transformer. Diode still measures fine btw. I also replaced the eletrolytic capacitors around that area.

[niblettr]

Re: PS50C550 sound but no picture.

Attached is now how I achieve proper power up.

What happens is that DRV reset it driven high by a fault, the control board detects DRV RESET and asserts DS Error high.
DS ERROR drives output enable of octal buffer that interfaces control board ribbon to Ysus. So in effect DS ERROR disable signals from control board.

Struggling to understand what drives the DRV RESET line.
I'll post some pictures of the PCB traces showing DRV reset.

[niblettr]

Re: PS50C550 sound but no picture.

see attached traces of back of pcb with highlighted labels

[niblettr]

Re: PS50C550 sound but no picture.

See more notes highlighted in red in attachment.

[niblettr]

Re: PS50C550 sound but no picture.

Does anybody know what error Does DRV_error detect?

[fzabkar]

Re: PS50C550 sound but no picture.

Here is the service manual, if you don't already have it:

http://elektrotanya.com/samsung_ps50.../download.html

[niblettr]

Re: PS50C550 sound but no picture.

Thanks, already got those although not much help in this case.