Panasonic plasma TC-P42S30 transistor on SN board blows 1 second after power on.

[mattpd]

Here is the service manual I found:

If you look on page "S-36" you will see the problem board. When I first got the TV, It would not power on and gave a 14 blink code. I see that 14 blinks is not listed in the service manual but I tripled checked the count and it was 14. There were 4 blown transistors that I replaced from a donor board. These were Q401, Q402 and two others that I don't remember off hand.

After this repair attempt when I turn on the TV I get sound and picture for 1 second and then the TV shuts down with a 6 blink code. I pulled the board and checked all the components that I replaced, and they were still good but transistor Q441 was shorted. I replaced Q441 and again it comes on for 1 second and then 6 blinks. I only have one more of these transistors left so I need to find why it is shorting before trying again. Any ideas?

And on another note, why is it that in the service manual if you look on page "S-50" Q441 is not listed. In fact the lowest part number is Q1101 and it goes higher from there... Am I missing something?

[tom66]

Re: Panasonic plasma TC-P42S30 transistor on SN board blows 1 second after power on.

The part numbers on Panasonic schematics start with a prefix, e.g. "16", "21" then the part number. So Q411 might be Q16411, or whatever the prefix is for the SN. Have you checked if you are getting good Vs (around 200V)? Any defect with the picture when it's working for that one second? Will set work with transistor missing?

[mattpd]

Re: Panasonic plasma TC-P42S30 transistor on SN board blows 1 second after power on.

Thanks for the quick reply, and thanks for the tip.

It did see some horizontal lines when it powered on the first time, but I am almost certain it was because the ribbon cables were not seated completely. I will try the board with the transistor removed tomorrow. As far as testing Vs, can you advise the proper procedure?

[tom66]

Re: Panasonic plasma TC-P42S30 transistor on SN board blows 1 second after power on.

There is a test point on the power supply. You can check across the Vsus points, near "Discharge". You should get around 200V, but the exact figure will be written on the panel sticker.

[mattpd]

Re: Panasonic plasma TC-P42S30 transistor on SN board blows 1 second after power on.

Ok, I will try both things tomorrow.

[mattpd]

Re: Panasonic plasma TC-P42S30 transistor on SN board blows 1 second after power on.

So, I hooked the board up with the transistor missing. I think I heard a pop when I powered on the TV. The TV came on with no blink codes, but there was also no picture or sound. Unfortunately there is now a short to ground somewhere... Any tips on locating the part that has the short?

[tom66]

Re: Panasonic plasma TC-P42S30 transistor on SN board blows 1 second after power on.

You would have to test every transistor. No quick way that I'm aware of.

Are you sure the part is a transisor? For example you aren't replacing a diode? If it is a transistor, it's definitely the right type? (IGBT and MOSFET are not typically interchangeable.)

[mattpd]

Re: Panasonic plasma TC-P42S30 transistor on SN board blows 1 second after power on.

The replacement parts came off an identical board. I think 4 were MOSFET and one was some other kind of transistor. The only way I know this was by hooking them to a component analyzer. I cant find any information on these parts, i guess because they are manufactured by Panasonic.

After some more investigation I have noticed that there is NO picture for the 1 second the TV comes on, only sound. Also, I found the short. It was in all 4 of the MOSFET I replaced. So I think there are 5 different transistors that blow as soon as the TV is powered on. Q401, Q402, Q421, Q422, and Q441.

[tom66]

Re: Panasonic plasma TC-P42S30 transistor on SN board blows 1 second after power on.

I would suspect the SN buffer chips unfortunately they're not on a separate buffer so you're SOL if you want to replace them unless you like soldering 128 pin QFPs.

[mattpd]

Re: Panasonic plasma TC-P42S30 transistor on SN board blows 1 second after power on.

Is that one of the 12 Panasonic chips that are glued to the board? Just out of curiosity is there a way to tell which one is bad? I do have some chip-quick and a rework station, so its not out of the question to swap one, although that glue on the pins makes me think twice. It's all for fun/learning now anyway as I have already ordered a new board to get the TV working.

[tom66]

Re: Panasonic plasma TC-P42S30 transistor on SN board blows 1 second after power on.

Yeah, it's those ones. If you can isolate the sus waveform to them, you can feed them 12V DC and see which gets hot... but as they're on the board, it could be tricky.

This thread has someone trying it with an LG: https://www.badcaps.net/forum/showthread.php?t=23438