Panasonic Plasma TX-P42ST31B - broken screen

[jdwis]

Hi guys

I am new to Plasma & LCD TVs concept.
I know quite basics of electronics repairing, might not be called genius but to quite a good level.

My friend has got a Plasma TV model no TX-P42ST31B. The screen is broken and asked me if it can be fixed, advised its no good idea as its gonna cost nearly same or more than a new TV. So another option was if he could sell any possible good parts from it.

I have opened it and tried checking it but as I m new to this Plasma TV concept so have no much clue from where to begin. My general sense tells me to check it from Power supply. There are 2 fans on the back as well.

All the boards and connections are properly connected, when TV is switched on, 2 relays try to switch on, fan does not spin, the front LED light flashes red for 7 times and just for quick 2 seconds there is high pitch noise somewhere from the bottom, then nothing happens and the LED flashing cycle continues.

What do I do now, where should I begin.
Thanks

[tom66]

Re: Panasonic Plasma TX-P42ST31B - broken screen

If the TV worked before the screen got broke, then all the parts should be good.

The "SC" board is in particular demand right now and sells for about £50 and you should be able to sell that fairly quickly. The "A" board is also a common failure, and you can expect a similar price.

The other parts might be worth £20~30 each but you could find it difficult to sell them.

Replacing the screen is uneconomical.

Note: I have a feeling that on this chassis a dead/cracked panel will lead to 7 blinks, however it COULD indicate a failed SC board, possibly damaged by the cracked panel.

[jdwis]

Re: Panasonic Plasma TX-P42ST31B - broken screen

If the TV worked before the screen got broke, then all the parts should be good.

Thanks tom66 for the info.

If the screen is broken, is there any way to check which boards are working, like by disconnecting any connectors and checking voltages at any test points?

[tom66]

Re: Panasonic Plasma TX-P42ST31B - broken screen

You can check for good Vsus (200V or so); this will indicate if PSU is good and output is not shorted.

Sometimes the SN and SS have LEDs on them.

Note this TV uses a combined SC and SU/SD, to make one board, SN.

[jdwis]

Re: Panasonic Plasma TX-P42ST31B - broken screen

You can check for good Vsus (200V or so); this will indicate if PSU is good and output is not shorted.

There is no printed mark or sign for "Vsus" (or "Va" or "Vs" like other plasma power supplies) anywhere on this power board?
As you can see from above pic there is only 1 cable with 2pins going from Power supply to "sc+su+sd = SN board (left board), should I check the voltage there?

[tom66]

Re: Panasonic Plasma TX-P42ST31B - broken screen

Yes, that is the Vsus power connector. Be ware with 7 blinks it will shut off quickly.

I am going by some Panasonic PSUs that have these test points. This is a very new generation 2011 plasma, I haven't seen inside one of these. I have only seen inside a 2005 (I think) and 2010 generation.

Another thing -- if panel is cracked it should buzz loudly until it shuts down.

[jdwis]

Re: Panasonic Plasma TX-P42ST31B - broken screen

I had removed all the boards for inspection for any short etc but couldnt find anything so I need to connect all that again, once connected and checking the voltage I will update here soon.
For some basic understanding I was just going through some service manuals and with your knowledge I could understand those names for the boards, yes it does say SN, A, SS, C1 & C2.

[jdwis]

Re: Panasonic Plasma TX-P42ST31B - broken screen

I have now connected all the boards and cables, kept note of all voltages at various test points, here are those..

The details are of 2 conditions, once power on and then the voltage levels in next 15-20 sec...
SN Board:
# VSUS 207v in 15-20 sec it goes down to nearly 9,8,7 etc to 0
# TPVAD 74.... 0
# TPSOS6 4.28... 0
# TPSOS7 0.66 ... 0

SS Board:
# TPSOS8 5.. 0
# TPVe 155... 0
# TPSS1 (H.V. Dnager point) 40... 0
# VeRef1 2.5 .... 0
# VeRef2 2.5 ... 0
# P15v 15 ... 0
# P5v 5 ... 0
# TPSUS 207 ... 0

it seems all voltages are coming and then dropping, do u think is there any short in any boards or is it just the Protection mode kicking in due to broken screen.

[tom66]

Re: Panasonic Plasma TX-P42ST31B - broken screen

I would guess protection mode. Nothing seems obviously abnormal.

[jdwis]

Re: Panasonic Plasma TX-P42ST31B - broken screen

I would guess protection mode. Nothing seems obviously abnormal.

cheers tom thanks.

[tom66]

Re: Panasonic Plasma TX-P42ST31B - broken screen

In the worst case, any defect will be limited to the SN (scan board) == Y-sustain. Offer a return policy on the parts in case they are failed.

[jdwis]

Re: Panasonic Plasma TX-P42ST31B - broken screen

In the worst case, any defect will be limited to the SN (scan board) == Y-sustain. Offer a return policy on the parts in case they are failed.

Great, thanks.