Samsung PN50C6500 No picture, sound good

[dougw03]

Hello,

I did some research and stumbled upon these forums. I have a Samsung Pn50C6500 and it recently randomly shut off and will turn back on but have no picture. Sound is fine, just no picture. I think it may be the XSUS YSUS or main logic board. As far as inside the panel, all of the caps look okay and the main logic board LED's are still blinking. So how can I determine which board is the problem? I would rather not buy all three boards if possible. I have a multimeter available, but no oscope or any other equipment for diagnostics. Any help would be appreciated. Thanks!

[tom66]

Re: Samsung PN50C6500 No picture, sound good

If turned on in a dark room do you see any glow from the screen at all?

Try unplugging the X sus and see if it turns on. It should turn on with a dim picture if this board is shorted.

[dougw03]

Re: Samsung PN50C6500 No picture, sound good

It is completely dark with no glow. I unplugged both the power and ribbon cables (I couldn't disconnect the buffer without removing the boards) from the XSUS and there was a flash of grey/black when I turned the TV on then the screen went black again. I also could hear the buzzing that I normally hear from the TV. I proceeded to unplug the TV then reattach the XSUS and saw a large spark at the XSUS board power connector. I realize I probably should have waited for the caps to discharge. Is this enough evidence to assume the XSUS is the problem?

[tom66]

Re: Samsung PN50C6500 No picture, sound good

Do you get a flash with the X SUS connected?

[dougw03]

Re: Samsung PN50C6500 No picture, sound good

No I do not.

[tom66]

Re: Samsung PN50C6500 No picture, sound good

Usually a dud X sus would give a dim picture... I would say Y sus first.

[dougw03]

Re: Samsung PN50C6500 No picture, sound good

Ok I'll go for the YSUS. Is there anything I can do with an oscope or DMM that might help me know for sure? Thanks!

[tom66]

Re: Samsung PN50C6500 No picture, sound good

You have a scope? You didn't mention this .

You can check the Y sus and X sus waveforms, there's usually a test point.

Use a 10X probe. The outputs from Y sus peak to 380V sometimes. Test relative to metal case.

[dougw03]

Re: Samsung PN50C6500 No picture, sound good

Ok so I am getting a 10X probe on monday. I've never worked with such high voltages and an oscope, are there safety precautions I need to take before I measure? In the meantime, here are the test points I found
http://www.flickr.com/photos/27836521@N07/7626108936/
http://www.flickr.com/photos/27836521@N07/7626103082/

Should I be looking for a particular waveform? Thanks

[tom66]

Re: Samsung PN50C6500 No picture, sound good

Ok so I am getting a 10X probe on monday. I've never worked with such high voltages and an oscope, are there safety precautions I need to take before I measure? In the meantime, here are the test points I found
http://www.flickr.com/photos/27836521@N07/7626108936/
http://www.flickr.com/photos/27836521@N07/7626103082/

Should I be looking for a particular waveform? Thanks

The precautions are:
- Use a fixed 10X probe
- Use a 10X probe which can withstand 400V

You're looking for the waveform which goes to the buffer boards.

[dougw03]

Re: Samsung PN50C6500 No picture, sound good

The precautions are:
- Use a fixed 10X probe
- Use a 10X probe which can withstand 400V

You're looking for the waveform which goes to the buffer boards.

Hmm I didn't see anything but a couple 100mv of what appeared to be noise on the test points for both the xsus and ysus. The only input that showed anything was the RST which was a square wave. Does this tell you anything?

[tom66]

Re: Samsung PN50C6500 No picture, sound good

It tells me that Vs is probably very low or some enable signal (aside from RESET) is not getting through.

[dougw03]

Re: Samsung PN50C6500 No picture, sound good

Hm, so this sounds like a power supply issue?

[tom66]

Re: Samsung PN50C6500 No picture, sound good

Test the Vs with your meter; it should be marked on the power supply.

[PowerAmpFreak]

Re: Samsung PN50C6500 No picture, sound good

Do you have proper VS and VA from powersupply at all?

[dougw03]

Re: Samsung PN50C6500 No picture, sound good

For both the XSUS and YSUS boards...
Vg 20V
Va 60-66V
Vs 216V

[dougw03]

Re: Samsung PN50C6500 No picture, sound good

Anyone have any ideas?

[tom66]

Re: Samsung PN50C6500 No picture, sound good

Vs looks a bit high should be closer to 200V. Is Va unstable?

[dougw03]

Re: Samsung PN50C6500 No picture, sound good

Va fluctuates between 60 and 66V.

[dougw03]

Re: Samsung PN50C6500 No picture, sound good

Can anyone please offer some advice about which board to switch first? I've been without TV for a long time now. THanks!