Problems After SC Board Replacement - Panasonic G20

[spmurph]

I had a "certified" Panasonic tech come out to service my G20 plasma. Set was dead with seven blinking lights. He diagnosed it as a bad SC board.

Replacement seemed to fix it, but after he installed it, I noticed what looked like purple snow in the bottom left-hand corner and, depending on the video source, horizontal bars would appear periodically. He came back to look at it and made sure all the buffers were connected. He called Panasonic and they sent him out another SC board. He replaced that one, same problems. He also swapped out another board but I can't remember which one. Doesn't matter because that didn't work either.

Here are some pictures of what the problem looks like:

Purple Snow:


White Bars:



The tech took some picture and said he was going to send them to Panasonic and get back to me. That was two months ago

[tom66]

Re: Problems After SC Board Replacement - Panasonic G20

You have a common issue.

The tech has not adjusted the VAD after replacing the board, which is listed in the service procedure for this panel. Most techs don't realise every panel is different and VAD or VSUS needs to be adjusted to suit each panel. You can either increase VSUS to compensate, or adjust VAD to what it should be. VSUS is easiest, but VAD adjustment will eliminate any IR (image retention) effects as well.

You will need a digital multimeter and a plastic screwdriver.

[tw2005]

Re: Problems After SC Board Replacement - Panasonic G20

The full model number of this TV is? If it's p42G20,p46G20,p50G20,P54G20 etc i think we're going to find the SC will be a TNPA5081. There's no adjustment on the SC, or SS and probably no panel sticker with voltages either.

I have not found any info in the manuals either like the generation before this. In the service menu you can select VSUS low / high. best to download the service manual yourself and have a read. maybe change the level there and see what happens.

I belive the PSU may have voltage adjustments there but the manual does not mention anything about them either.

i can't make much with such a close up but the second pic with the bands i'm wondering if it's the buffer boards?

SC and buffers are a common fail if this is a model with the TNPA5081. A boards as well.

Maybe get into the service menu and run the inbuilt patterns and the picture inverting procedures to see if it's generated by the A board or a panel issue?

I have not faced this symptom before so I'm just throwing some other ideas out there,

Was there any documentation telling what was done? It'd be helpful to know what the other board was, would Panasonic have records on it?

[spmurph]

Re: Problems After SC Board Replacement - Panasonic G20

It is a P50G20.

I am not sure what the other board he tried to replace. Whichever one it was, he didn't come to the conclusion from testing because every time he was here he had to call Panasonic and troubleshoot over the phone with them. I guess I could get that information from him.

[tom66]

Re: Problems After SC Board Replacement - Panasonic G20

If you could take a photo of the SC and P boards we can indicate where to test and adjust.

[tw2005]

Re: Problems After SC Board Replacement - Panasonic G20

Jumping the gun a little here Tom, but this should be the board Rev AW I believe. The one I have here was shipped from the UK and was out of the TX-P50G20B. At least that's how it's marked.

PSU I can't be 100% on but the adjusting pots are the same Vr251,Vsus & Vr401,Vda.

[tw2005]

Re: Problems After SC Board Replacement - Panasonic G20

It is a P50G20.

I am not sure what the other board he tried to replace. Whichever one it was, he didn't come to the conclusion from testing because every time he was here he had to call Panasonic and troubleshoot over the phone with them. I guess I could get that information from him.

The way i see it, your TV was fine before failure? 7 blink, SC board replaced( twice now with same faulty picture), No mention of buffer board replacement just connection check.

I would expect a "certified" Panasonic tech to be well and truly aware of this generations common failures and given a SOS7 can be Buffers,SC or both why would you not carry new buffers and a SC to a SOS7 callout.

If I just replaced the SC and saw that I'd swap out the buffers first before I tried another SC.

What worries me are the buffers sus but not damaged enough to blow the SC in the short term but potentially the SC could go again.?

I could be completely off track but highly suspicious. It'll be interesting to see how you go with it. I've still got the back off mine if we need an idea what voltages these run at although my panel may be a different version MC127F19M13.

yours could be Number: MC127F19R13 which has the REV AW SC or if it's the same as my panel probably the AF

[tom66]

Re: Problems After SC Board Replacement - Panasonic G20

We don't touch Vda; we touch Vad. Vda adjustment has the potential to damage the panel COF drivers, which are not replaceable. However, it looks to me, like Panasonic have made everything non-adjustable, so we may need to tweak Ve, if available, and Vsus, to compensate. Or an exact SC must be used.

[tw2005]

Re: Problems After SC Board Replacement - Panasonic G20

What you see is all there is Tom. The SC has Vsus, 15V, 5V. The SS has Vsus 15V,5V.
The A board i suspect controls the others on the SS and SC?

[tom66]

Re: Problems After SC Board Replacement - Panasonic G20

I suspect Panasonic have got their panel tech so precise that they don't need adjustments any more. Even on 2008 panels there is only Vad on the SC and Ve on the SS, and Vad is specified as a fixed -140V.

[tw2005]

Re: Problems After SC Board Replacement - Panasonic G20

Don't know but it's Panasonic, probably smarter than the average.

[tom66]

Re: Problems After SC Board Replacement - Panasonic G20

It probably comes down to labour costs.

Japan, where Panasonic makes most of its panels, has high labour costs, and so they try and minimise the amount of hand-tweaking the engineer has to do on each panel, maximising the panels they ship and minimising the per-unit labour cost. To do this, they have to invest in more precise machinery and have a higher quality control standard.

Korea and China, where Samsung and LG make most of their panels, have low labour costs, so the extra cost of making the panel more precise is not necessary because it is economical to have an engineer sit their and tweak the pots. Overall Samsung and LG PDPs are cheaper to buy for OEM use, the labour cost and lower manufacture costs are likely the main reasons.

[sun130]

Re: Problems After SC Board Replacement - Panasonic G20

I have a TXP50VT20 with similar problem...but am only someone at the 'replace a board' by elimination process .I find it difficult to understand a Panasonic technician not replacing all three boards...SC, SU, SD. as it seems common for failures to be in more than one.
I have read in equal numbers the opinion that they "should all be replaced at the same time" and "replace only the SC" ...which of these is correct?
I have a replacement SC board on its way but have tried trawling around to find an idiots guide to testing my buffer boards without success...I think that I need to do this at least AND be able to test any second hand replacement before fitting .....I am no techie but would appreciate any help

[vinceroger69]

Re: Problems After SC Board Replacement - Panasonic G20

tom66 guide is good
http://www.youtube.com/watch?v=51SZsfH60EY

[tw2005]

Re: Problems After SC Board Replacement - Panasonic G20

you'll need a multimeter capable of measuring above 6 Megohms but generally if the buffers fail there'll be a short or resistance goes substantially lower..

This is for the V20 but pinouts are the same for these tests, They quote 2.2Mohm for Vfo but the results I've seen on mine are around 1.9M.

As for the Sc, all you can do really is do a quick test for short on Vsus at Sc2, and go around the board and check all the heatsink mounted transistors for dead short across their legs.

If you're still unsure about the buffers but want to test the SC with power, connect the board normally,leave the buffers disconnected then you short the 2 pins at SC50 together on the SC, power the Tv and if the TV turns on then that confirms the Sc passed.

[sun130]

Re: Problems After SC Board Replacement - Panasonic G20

Thanks for the help......I've watched the TOM66 video many times but cannot figure how to apply it to my TNPA5336 and TNPA5337 boards, they are so different...Where is the "Y main output" ?...there are only the SU41,SD42 and SD46 connectors......am I making any sense?.......The SC test I understand and can do......Maybe this is all just beyond my capabilities......

[tom66]

Re: Problems After SC Board Replacement - Panasonic G20

I recommend tw2005's guide above over my video for Panasonic plasmas. Easier to do, more reliable.

[sun130]

Re: Problems After SC Board Replacement - Panasonic G20

Thanks for the help...............tw2005, can I see the rest of the document that this thumbnail came from?..I think it might be interesting reading....
thanks

[tw2005]

Re: Problems After SC Board Replacement - Panasonic G20

Thanks for the help...............tw2005, can I see the rest of the document that this thumbnail came from?..I think it might be interesting reading....
thanks

https://www.badcaps.net/forum/showth...=26322&page=11

post 201

What SC board have you got? Your SD/SU board numbers have me curious, I was expecting TNPA5090,91

[sun130]

Re: Problems After SC Board Replacement - Panasonic G20

Yeh....it wasn't a test !!.....Stupid me picked up another set that I happened to have..Sorry my mistake. Of course you're right, the boards are TNPA5090,91.
I had already found the rest of the document and am learning/reading without actually doing anything yet.....
Thanks once again...