Greetings all,
Trying to troubleshoot a Samsung PS58C7000 with working functions and sound but no picture.
Have tried replacing the y-main board, but no change.
Vital signs are all good, Vs209, Va55, Ve90, Vsc-200. Vsch I think was about -40.
Logic heartbeat LED regular on/off 1 sec.
The panel is firing up and switching on blank - no signs of cracks or physical damage in that state but I don't really know for certain the history. "just stopped working" is all I have to go on.
Removing either y-buffer 1 at a time results in the top/bottom half the panel switching on but still blank.
With x-main disconnected no noticeable change.
A fairly quick probe of y-buffers between va/gnd and the buffer outputs and I didn't get any beeps, but I will be going back and checking them more carefully before going much further.
According to Mr Google-search, and the 2nd hand price difference of the upper/lower buffers, the lower y-buffer seems to be the common fault in these.
However if it was just the lower y-buffer with the problem i might would have expected to see the top half of screen working ok once the damaged lower buffer was removed? and that was not the case. or vice-verse. There is definitely another post around here for a faulty y-main with a Pxxxc7000 that only has 1 y-buffer installed and still gets an image on that half of the screen, and i just get blank, illuminated but blank.
I read a post somewhere that basically said the small ceramic caps on the y-buffers that are "heatsunk" opa-samsung style- using blobs of hot glue, can fail. But again not sure if that would explain my symptoms- or how to test for it other than removing them all and testing them individually.
Questions:
1/ Any ideas? - before i distract you any further
2/ Do the X or lower buffers on these ever have problems?
3/ Would a logic main be likely to show a healthy heartbeat but still have a problem that stops the lvds signal passing through correctly?
4/ Any quick and dirty ways of testing the x-main and buffers? or lower buffers?
Now I'm leaning towards maybe the x-main but since Ve voltage was ok on the x-main i looked elsewhere and never really checked it.
As x-mains go, what are the common signs of failure on them? Are they basically the same as y-mains with failed mosfets etc?
The reason I replaced the y-main is probably moot to try and explain now, but one of the mosfets was buzzing loudly and tapping its heatsink very lightly made the noise come and go and change frequency etc, so i was possibly mislead by the noises. I also thought it looked like the signals were making it from the logic to the y-main ok, just using a dmm on the test points near the input ribbon i could see some flickering to suggest a signal present, but couldn't really see any signal when i probed the same lines on the buffer/output side of the y-main which appeared to the dmm to be mostly all between -97v and -100v and static.
I want to learn how to safely use a scope to verify these types of things on tvs in future, especially since tinkering with plasmas particularly is becoming more of a regular hobby. Tips or links etc specifically on using a scope for tv repair and diagnosis would be greatly appreciated too.
I might get back and post pics or more details, but for now that's the nut of it. I have the service manual for the 50" but not the 58 and it's too large to attach here sorry.
Feel free to request pics or any info I've left out in the meantime.
Thoughts, suggestions and opinions all welcomed.
DD
Trying to troubleshoot a Samsung PS58C7000 with working functions and sound but no picture.
Have tried replacing the y-main board, but no change.
Vital signs are all good, Vs209, Va55, Ve90, Vsc-200. Vsch I think was about -40.
Logic heartbeat LED regular on/off 1 sec.
The panel is firing up and switching on blank - no signs of cracks or physical damage in that state but I don't really know for certain the history. "just stopped working" is all I have to go on.
Removing either y-buffer 1 at a time results in the top/bottom half the panel switching on but still blank.
With x-main disconnected no noticeable change.
A fairly quick probe of y-buffers between va/gnd and the buffer outputs and I didn't get any beeps, but I will be going back and checking them more carefully before going much further.
According to Mr Google-search, and the 2nd hand price difference of the upper/lower buffers, the lower y-buffer seems to be the common fault in these.
However if it was just the lower y-buffer with the problem i might would have expected to see the top half of screen working ok once the damaged lower buffer was removed? and that was not the case. or vice-verse. There is definitely another post around here for a faulty y-main with a Pxxxc7000 that only has 1 y-buffer installed and still gets an image on that half of the screen, and i just get blank, illuminated but blank.
I read a post somewhere that basically said the small ceramic caps on the y-buffers that are "heatsunk" opa-samsung style- using blobs of hot glue, can fail. But again not sure if that would explain my symptoms- or how to test for it other than removing them all and testing them individually.
Questions:
1/ Any ideas? - before i distract you any further
2/ Do the X or lower buffers on these ever have problems?
3/ Would a logic main be likely to show a healthy heartbeat but still have a problem that stops the lvds signal passing through correctly?
4/ Any quick and dirty ways of testing the x-main and buffers? or lower buffers?
Now I'm leaning towards maybe the x-main but since Ve voltage was ok on the x-main i looked elsewhere and never really checked it.
As x-mains go, what are the common signs of failure on them? Are they basically the same as y-mains with failed mosfets etc?
The reason I replaced the y-main is probably moot to try and explain now, but one of the mosfets was buzzing loudly and tapping its heatsink very lightly made the noise come and go and change frequency etc, so i was possibly mislead by the noises. I also thought it looked like the signals were making it from the logic to the y-main ok, just using a dmm on the test points near the input ribbon i could see some flickering to suggest a signal present, but couldn't really see any signal when i probed the same lines on the buffer/output side of the y-main which appeared to the dmm to be mostly all between -97v and -100v and static.
I want to learn how to safely use a scope to verify these types of things on tvs in future, especially since tinkering with plasmas particularly is becoming more of a regular hobby. Tips or links etc specifically on using a scope for tv repair and diagnosis would be greatly appreciated too.
I might get back and post pics or more details, but for now that's the nut of it. I have the service manual for the 50" but not the 58 and it's too large to attach here sorry.
Feel free to request pics or any info I've left out in the meantime.
Thoughts, suggestions and opinions all welcomed.
DD
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