Samsung PS42C96HD no glow, Vs=0

[senndogg]

Re: Samsung PS42C96HD no glow, Vs=0

and the other board

[senndogg]

Re: Samsung PS42C96HD no glow, Vs=0

yes. thats -190V in there.

[tom66]

Re: Samsung PS42C96HD no glow, Vs=0

Same procedure for that board but check VE instead. Panel will have VE rating written on it, expect from 80 to 150V.

And... do you have a scope? It is necessary for checking ramp waveforms...

[senndogg]

Re: Samsung PS42C96HD no glow, Vs=0

Ve 97V
Va 63V
Vs 204V
Vsc -90V (expected -190V)

these are the same as written in the panel except Vsc
i know you asked me 3 times Tom, and the answer is no, i dont have a scope. i can measure Hz with my multimeter but i know you are looking for the waveform. if there is conclusion without checking ramp, please tell me. i

[senndogg]

Re: Samsung PS42C96HD no glow, Vs=0

sorry Tom, Vscan is -190V, Vsc is -90V. Does this mean anything?

[tom66]

Re: Samsung PS42C96HD no glow, Vs=0

Vsc should be more than -90V. That is too low IMO.

You can do some voltage checks but plasmas are hard to repair without knowing what voltages to always expect in those places, which is where a scope comes in handy.

I can't see a point for VSET, can you see one?

[senndogg]

Re: Samsung PS42C96HD no glow, Vs=0

No Tom, i fail to see any Vset testpoint in both boards. Is this weird?
This is the service manual but there is no indication there. I extracted sth about "ramp" where your suggestion of the scope is very useful. Now (reading a bit in other threads) i am starting to understand a bit about plasmas.

[senndogg]

Re: Samsung PS42C96HD no glow, Vs=0

the manual.

[tom66]

Re: Samsung PS42C96HD no glow, Vs=0

Yes, the ramp is used to release the electrons from the gas making it ionised, called priming. Then sustain pulses make written pixels light up. Priming makes the screen glow slightly with no image. No priming = no glow and faint or no image.

[senndogg]

Re: Samsung PS42C96HD no glow, Vs=0

what about the low Vsc? i just measured it, and its just showing -60V. maybe a faulty board?

[tom66]

Re: Samsung PS42C96HD no glow, Vs=0

Yeah, that is too low... Is -Vscan too low too?

[senndogg]

Re: Samsung PS42C96HD no glow, Vs=0

no. steady -190V in every test. its strange that hours ago Vsc was at the -90 range and now just -60.

[tom66]

Re: Samsung PS42C96HD no glow, Vs=0

That could possibly cause your issue. Check it with the buffer boards unplugged too.

[senndogg]

Re: Samsung PS42C96HD no glow, Vs=0

still -60V with the y-buffer disconnected.

[tom66]

Re: Samsung PS42C96HD no glow, Vs=0

Try adjusting Vsc/Vscan potentiometer what happens?

[senndogg]

Re: Samsung PS42C96HD no glow, Vs=0

The Vscan moving from 170-195V...
Anyway, thank you to everyone especially Tom for helping me, but i have to give up! This tv costs me a lot of room in my working space, and also valuable time. And at this season of the year i am overloaded with work...Maybe it would have been very simple if i had the right tools and some spare parts.
Plasma tv are very challenging because of their complexity, and this determined me to have it stripped for 10 days. But i have to admit i am still not familiar with them, and still holding the negative record of fixing 0 plasmas with sustain/buffer problems (2 fixed had psu issues).
Cheers everybody and thanks again!