Panasonic Plasma 42PV80LB 7 Blinks, VSCN too high

[Biruslapio]

Hello I'm struggling with this old plasma TV and its SC board, TNPA4393, I've measured the SU/SD buffers, every IGBT and transistors, gate drivers, SMD diodes, optocouplers etc, no shorts or suspecting measurings, at least with they soldered on the board.

VSUS - 187V
VDA - 75V
VE - 130V
VSET - 320V
VAD - (-149V)
16V_F
5V_F A/B
15V

All voltages are normal except for VSCN, which according to the service manual is supposed to be 145V+-4V, it is always 205V.
VSCN voltage is fixed, generated and measured from VAD as ground, even if I lower VAD to -112V("minimum" allowed by the trimpot), VSCN doesn't change.
I have a working SC board from 42PZ80LB (Full HD model) and it has the same component placing, except more transistors to handle increased power load.
I swapped between the SC boards the VSCN controllers (IC787 and IC786) and nothing changed, the 7 blink protection of VSCN and VAD is located on the A-Board.
No changes on the voltages with or without the SU/SD buffers plugged in, also the screen is completely dark always, no flashes.
IC786 is a MIP9L02 from Panasonic itself, no datasheets, VAD is generated by the same model IC(IC784).
https://www.electronica-pt.com/esque...gph11da-14476/ link to service manual (portuguese only).

[Biruslapio]

Re: Panasonic Plasma 42PV80LB 7 Blinks, VSCN too high

Okay, for some reason for now the TV "fixed itself", I hooked up my oscilloscope on the VSCN line, and powered on the TV, then VSCN jumped to 207V, there was a quick descend to ~130V, but it went up to 207V again until the caps lost their charge. Everytime VAD or VSCN(I don't know which one) started to discharge the SC made an horrible screeching noise.

Then I tried powering on about 10 times, two of these times it went to 146V and stayed there until 7 blinks, the buffers were isolated, I plugged/screwed them in. The TV powered on, there was image and everything else was working perfectly.

When the SC produced the correct VSCN of 146V there was way less screeching.

Of course this fault will come back anytime I imagine, there is no miracle fix here, for now I will let it heat on and off multiple times, leave it some days unpowered, etc.

Also when I bought this TV it was plagued with dust, since 2008 it never had a fault and was never opened according to the owner, it was true, I ended up washing all the boards and connectors, resoldered with a hot air station some SMD components at YSUS board because their pads were blackened by the dust, maybe it helped.

The service menu image test shows clearly that the coating in the glass has been wearing out, results of humidity, heat and many hours of use, a pity, and everyday I'm seeing more and more plasmas having this problem, also some old LCDs.

Look at that 37157 hours count, 11946 times powered on, that's the highest I saw yet.