Poor black levels following Panasonic TC-P46S30 SC board replacement

[darkTime]

Here is the situation (I previously mentioned this in one of the other 14 blink threads):
- I purchased a used TC-P46S30 plasma with 14 blinks and following the testing procedures found in this forum (many thanks again), I discovered that the SC board was the culprit (the SU and SD boards and everything else tested fine)
- I purchased a cracked-screen TC-P50ST30 to scavenge its SC board (which appears to be similar if not exactly the same as the one in the TC-P46S30)
- The SC board from the ST30 tested fine and I went ahead and installed it in my TC-P46S30
- TV works, picture is great and I have had it on for hours at a time for over a week

BUT...

- the black levels are significantly worse than I have seen on similar models from this line of TVs and TV gets IR much faster than I would expect
from experience with similar plasma TVs
- I assume this is because the SC board is from a different model

QUESTIONS:
- are there anything that can be done to remedy this situation? I would really like to make something of the current setup (my soldering skills are pretty poor).

[tom66]

Re: Poor black levels following Panasonic TC-P46S30 SC board replacement

The black level on these sets is pretty good, so what you are seeing is abnormal. These sets use a scanning reset black level. Looking closely at the panel you should see some thin, brighter lines scanning up or down the panel. This is a slightly higher reset potential being applied to the panel but for a lower duty cycle. If you can see this, it indicates the black level is probably normal, and maybe something else is wrong.

Try adjusting the user brightness control in the menu. This can increase apparent black level. It should be, in most cases, below 50%. In general: brightness adjusts the black level and contrast adjusts the white level.

[darkTime]

Re: Poor black levels following Panasonic TC-P46S30 SC board replacement

I have tried all of the typical user accessible adjustments, nothing fixes the problem.

I am pretty sure the problem stems from the SC board coming from a different model TV.

Are there any voltages that can be checked and/or adjusted?

[tw2005]

Re: Poor black levels following Panasonic TC-P46S30 SC board replacement

Both the 50ST30 and the 46S30 have 215V as a reference for Vsus LO (selected in the serv menu).

The caps appear to be the same but the induction coil, L411 has a different part number between the 2 models

Usually I find caps and coils are the usual variations between the few boards I've compared between 46 / 50"

L16411 G0CR37KA0216 (46")

G0CR32KA0216

No idea if that has anything to do with it or if maybe it's running normal and you're just disappointed with this model.

[darkTime]

Re: Poor black levels following Panasonic TC-P46S30 SC board replacement

Both the 50ST30 and the 46S30 have 215V as a reference for Vsus LO (selected in the serv menu).

The caps appear to be the same but the induction coil, L411 has a different part number between the 2 models

Usually I find caps and coils are the usual variations between the few boards I've compared between 46 / 50"

L16411 G0CR37KA0216 (46")

G0CR32KA0216

No idea if that has anything to do with it or if maybe it's running normal and you're just disappointed with this model.

Thanks for looking into all that, I really don't have much background in
this area.

Is the difference you found the only difference (outside of the normal variations you mentioned)?

I had the 42" model in the S30 series, and the black levels were great, so I think my expectations are realistic. For reference, the black levels in a pitch black room are similar to a cheap Benq TN-panel based LCD I have attached to my computer.

[tw2005]

Re: Poor black levels following Panasonic TC-P46S30 SC board replacement

Thanks for looking into all that, I really don't have much background in
this area.

Is the difference you found the only difference (outside of the normal variations you mentioned)?

I had the 42" model in the S30 series, and the black levels were great, so I think my expectations are realistic. For reference, the black levels in a pitch black room are similar to a cheap Benq TN-panel based LCD I have attached to my computer.

Pretty much. I scanned through the cap list and compared side by side and surprisingly they were the same.

The board is matched to the panel size. Tom describes a PDP as a big Cap and last time I did this was on the 5081 sc boards and they have more differences but between the 46 and 50 on that one it was the inductors , polyester caps and maybe an electrolytic that was different.

I know nothing about black levels.

[tom66]

Re: Poor black levels following Panasonic TC-P46S30 SC board replacement

Black level is primarily defined by the priming/reset/initialise waveforms rather than the sustain waveform. How many power on hours does the set have?

When I was tweaking my Kuro, I could essentially turn off the priming/reset waves and get zero black. (Only problem was stuff became pink...)

[darkTime]

Re: Poor black levels following Panasonic TC-P46S30 SC board replacement

Black level is primarily defined by the priming/reset/initialise waveforms rather than the sustain waveform. How many power on hours does the set have?

When I was tweaking my Kuro, I could essentially turn off the priming/reset waves and get zero black. (Only problem was stuff became pink...)

The set has roughly 4200 hours on it. I am not sure if this is considered
a lot but the 42" (with great black levels) that I referenced in a previous post had about 2000 hours more.

I believe I watched a video of yours Tom where you were tweaking the blacks
on an earlier generation Panasonic. How where you adjusting the Vsus and Vad and does this methodology still apply to the S30 series?

Another bizarre thing about the TV is that if you are displaying several images with bright elements in succession, then switch
to a black screen, the black screen will have afterimages of all the bright elements. I have seen similar behaviour on other plasmas but
never to this degree.