Panasonic TX-P46VT20E flickering after ~25 min.

[fluxflux]

Hello Forum,

I have found a Panasonic Plasma TX-P46VT20E in the dumpster.

After letting the system sitting in the room for about 24h I've turned it on and it worked fine. The latest Firmware is also on it.

After approx. 20-25 min the picture begins to flicker (horizontaly ghost stripes) at the complete display and after 30 min it getting much worser.

I've turned it off again and after letting it cooling down the error is reproducable.

It seems that after 60 minutes the flickering getting less worse.

My Assumption: There is a heat/connectivity problem somwhere.

Question(s):

Do you know the specific problem or might have a clue where to start troubleshooting?

I have not yet opened it. My ideas.

- Using freezing spray to spot the area (Where to start?)
- Reflow processors.

I've uploaded a video. please download and rename it to .MOV

Kr

FluxFlux

[tom66]

Re: Panasonic TX-P46VT20E flickering after ~25 min.

Enter the service menu:

Switch TV on and switch to working input
Hold VOL- on the TV
Press the "0" button three times on the remote (If you do not have remote, you will need to buy one, but almost any Panasonic remote will work)

Wait a few moments...service menu appears

Press red and green to cycle through modes until you get a test pattern with gradients or grid pattern on it. See if this is also unstable.

If it is NOT unstable then this would most likely be a main board issue.
If it is unstable the issue requires further diagnosis.

Also, nice find, wish I found a 46" Panasonic plasma in the dumpster near me!!

[fluxflux]

Re: Panasonic TX-P46VT20E flickering after ~25 min.

Hi Tom66,

Thank you for your hints.

I've done a service menu test.

The flickering is still there.

For me it seems - as of the bright of the test pattern - it is a heat problem as it showed up after ~15 minutes. Does a Plasma heats up faster if it shows a bright picture?

(attached a still picture - the line at the bottom 3/3 indicates the flickering)

hmmm....

Can you recommend some troubleshooting-steps?

Kr

FluxFlux

[tom66]

Re: Panasonic TX-P46VT20E flickering after ~25 min.

I would get a hairdryer or a heat gun on a LOW setting (max 100C).
Then start heating up specific parts of the main video board.
You can use a toilet roll tube to isolate the heat to specific areas.

You want to see if heat makes the problem worse. You can also use a freezer spray but beware of condensation.

I would suspect the issue is the A board but we want to rule out the SC and SU/SD (signalling error possible).

[fluxflux]

Re: Panasonic TX-P46VT20E flickering after ~25 min.

Hi Tom,

Thank you.

I've removed the back cover and the TV is running now for about 50 min. without the issue.
Also removed a lot of dust.

Which one is the A Board?
I've never opened a Plasma before - just have some little expirience with LCD.

Will try the method you've suggested.

Kr

FluxFlux

[vinceroger69]

Re: Panasonic TX-P46VT20E flickering after ~25 min.

The a board is the one with hdmi/scart inputs on it

[fluxflux]

Re: Panasonic TX-P46VT20E flickering after ~25 min.

Hi all,

during the hoidays I've paused a bit.

What have I done so far:

A: Tried to heat up some parts of the Mainboard.
B: Tested the TV
a - with back cover on
b - without back cover
C: Measured the temp of the aluminium cooler at the mainboard.
a - with back cover on
b - withóut back cover
D: Done the TEST-Picture from Service menu again.
F: Further investigation

Results:

A: The Problem did not get better/worser.
B a: TV run more than 2 h (Batman Begins) without an issue (as of dust remove?)
B b: TV run more than 2 h (Batman Begins) without an issue (as of dust remove?)
C a: 49 Celcius
C b: 55 Celcius (I think as the back cover is not used as heat absorber)
D: Bad Picture was visible within ~14 min. (with no back cover)
E: Found a bad cap? on Power Supply Board (230V 820uf) ... (see pictures) ... Could that be the issue?



As of luck . I found a second hand TX-PVT20E with the 11 Blink (Fan-Error) for 30 €)

Next steps: Swapping Boards

Any suggestion/recommendations?

Kr

FluxFlux

[tom66]

Re: Panasonic TX-P46VT20E flickering after ~25 min.

That cap is fine, normal for those large ones to do that. Anyway, it is Vsus cap, if you have a problem it would be underdiffusion (pixels not firing up, trails behind moving objects, etc.) which would eventually cause a shutdown SOS6.

SOS11 is not always fan error, can be main board too.

[tw2005]

Re: Panasonic TX-P46VT20E flickering after ~25 min.

when these patterns occur, try going back into service mode the select Option. mirror option, 02. see if the distotion moves to the top. I can't make it out in the photo and the zip file kept coming up as invalid.

The test pattern you have posted is generated on the D board. Not uncommon for these to fail with heat and age, potentially BGA solders failing.

It's tucked in behind the Sub woofer. Try freezing/heating that or straight up swap it.

Both A and D boards fail in these

[fluxflux]

Re: Panasonic TX-P46VT20E flickering after ~25 min.

Hi Both,

@Tom66:

Thanks, All three fans of the second hand VT20 are klicking (as of a bearing ball issue?). I will first swap the Fans of the Dumpster VT20 to the Second hand VT 20 and see if the error (11 blink) occurs) If the TV is stable i will swap boards.

@tw2005:

Thanks, The Zip is not really a zip. I just renamed ist. Please remove the zip-extention by renaming it - SORRY :-). I have not heated up the D-Board. Will do it.

[fluxflux]

Re: Panasonic TX-P46VT20E flickering after ~25 min.

Hi,

It seems to be the D-Board.

I've measured the temperature and at 60 C the flickering starts.

To reduce the temperature I've put a cooling pad and an old heatsink on it (see picture).
With no backcover on the temperature is now ~50 C. (after an 2h movie)

I'll now put the backcover on and will do some testruns.

Question: Should I reflow / bake the CPU on the D-Board?

Kr

FluxFlux

[fluxflux]

Re: Panasonic TX-P46VT20E flickering after ~25 min.

Hi,

just a quick update:

The issue still exists with backcover on (still ~14 min with the test picture).

The meassured heat at the heatsink is 49 C,

Note; I haven't swaped the boards between the two sets. Will do so if I have time to replace the fans at the "second hand set"to test it.

Some thoughts: When I've heated up the D-Board the issue appears. Why? Does the heat goes up and heating some other areas? Maybe the Power Supply which is above.

THX

FluxFlux