LG 50PV350T sound but no picture. Help please

[niblettr]

Hi,
I removed the back off and did some probing around.
Va 55V GOOD
Vs 201V GOOD
Vy -90V GOOD
Vsc 150V GOOD
Vzb 130V GOOD
No faint glow on plasma screen. (Is there meant to be on a plasma?)
tested upper then lower y board, still no image.
Tcon board has flashing Led (not constant, maybe error code)
Zsus board has 2 heat sinks, one is luke warm, the other is very hot. (Water sizzles on it)
There is a wire link labelled 18V but measures 9V. (on the Zsus board)
I replaced the Zsus board but still get the above.
I checked both buffer boards and one chip on the upper board seemed to be shorted.
I removed this buffer board hoping bottom half would come on (dont know why I though upper board could stop lower board from work)
Any ideas where to look next? This 9v measurement concerns me a little.
Part number of the Zsus is EAX63551302 REV B

[niblettr]

Re: LG 50PV350T sound but no picture. Help please

Ysus heatsinks are stone cold event though high voltage is being generated by it to bottom Y buffer board.

[niblettr]

Re: LG 50PV350T sound but no picture. Help please

Also, if the same "working version" of this TV was to be powered up WITHOUT the Z sus board, would anything be seen on the screen? It would just be easier for me to concentrate debugging without that board plugged in for the moment...

[niblettr]

Re: LG 50PV350T sound but no picture. Help please

Oh, and fuses are all good. This model does not have IPMs that I can tell.
This TV is very similar to the LG 50PV450 looking at the pictures of the boards. Difference being that the main A/V digital board (HDMI connectors on it, not sure what the correct name for this board is) has more A/V connectors. All the other boards look identical.

I also tried disconnecting the LVDS cable and shorted the 2 test points to get test pattern and nothing. Screen will not power up.

[niblettr]

Re: LG 50PV350T sound but no picture. Help please

some more photo uploaded..

[niblettr]

Re: LG 50PV350T sound but no picture. Help please

Managed to temporarily fix the problem. For completeness, I'll list what I did to get it working in the hope someone else will benefit from this or can shed some light on that this particular part of the circuit does (I have no schematics..)

There is an 15V supply line on the Ysus that feeds the Tcon board. This was at 9v. I cut 15V line on the ysus and tcon still powered up (so it obviously gets its power source elsewhere)

15V line on y sus still measured low. I measured impedance of 15V line on tcon (ok)

With the tv turned on, I bridged the 15v back up and it sparked a little but nothing.
I did it a few times and now that that line measures 18V and screen came on and everything worked.

I suspect there is a dodge cap on that line that got temporarily resuscitated, but at least I know where the fault lies. Bad Y-sus. Will wait for TV to die again before I fix the problem properly.