Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

[MTWallet]

I've done a lot of reading the last few days to try and make sure I'm on the right track. Just asking to make sure there isn't something else I should check before diving in.

Kiddo was watching the telly the other day when it went out. He wasn't able to describe the exact circumstances, just that the picture went away. Older daughter tried to help by pushing power button and got the 14 blink code. I followed the shop jimmy diagnostic on youtube and found SC2 is shorted. No short on P board when the cable is disconnected. TPSC1 on SC board is not showing a short, so I did not diagnose the buffer boards any further. Removed SC board and SC2 is still shorted. Ordered the repair kit from shop jimmy and am awaiting its arrival.

I am just trying to cover my bases before I take this on, don't want to replace the transistors and plug it all back in just to have it blow again. Is there a way to test the buffer boards other than TPSC1, if so, should I since that point was not showing a short? I have read that some suggest replacing the buffer boards as well as the SC board, is that really necessary? I assume once I pull the transistors and resistors off the board (just the ones to be replaced!), I should no longer get a short between the pins on SC2? I saw somewhere that one model of SC board should have a 5Mohm reading on one pin and 0ohm on the other after replacing all the parts. I don't know if that applies to this board (TNPA5351 v2).

Finally, any recommendations on how to remove the heatsinks that are on a couple of the transistors? And then what to use to put them back on? Thermal tape good enough, or should I use a thermal epoxy?

Thanks for any input or direction on where to read more about this issue! And for the record, I am quite comfortable with a soldering iron and hot air rework station, so the physical task of replacing bits and bobs shouldn't be an issue. Thanks again.

PS, I will be away from the keyboard over the next couple of days, so I may be slow to answer any questions.

[MTWallet]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

So, should I assume no responses here means I'm on the right track?

Still looking for best way to remove those heatsinks though.

Got my parts in and am ready to start swapping parts tonight.

Thanks!

[Terryfictv]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Why remove heat sinks? Isolate which parts are shorted first!
Two pairs of FET's are the usual culprits....as a first step,
cut the legs of each, but do not remove FET until confirmed shorted with your meter.
Would you like the location numbers?

BTW, the resistors in the kit do not need replacement unless they check
open with your meter. The two diodes should be replaced along with the four FET's.
http://www.shopjimmy.com/panasonic-t...tc-p55st30.htm

[MTWallet]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Thanks for the reply! I'm all for only replacing what is broke, but not sure which pieces are bad at this point. I got a package from shopjimmy with 6 parts of one number FET and 2 parts of another FET, also a small strip of the resistors. There are no diodes, unless they started making them look like FET's! Locations shown on the packaging of the kit are Q401, Q402, Q403, Q421, Q422, Q423 for the 6, and D401 & D421 for the 2. The resistors show to go at R401, R402, R403, R421, R422 & R423. On my board, Q421-Q423 have heatsinks on them and are inaccessible without removing them. I don't have the kit in front of me at the moment or I would relay the numbers to you.

And yes, any info on what to check first would be quite helpful!

[Terryfictv]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

D401 & D421 are diodes. If you cannot get to a heat sink mounting screw,
it is sometimes much easier to remove large cap blocking your screwdriver !
Then put it back after you finish with the replacement of the shorted part.

[MTWallet]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Do you have a specific recommendation for testing the FETs? I only have experience with smaller NPN/PNP transistors.

As for the heatsinks, they are glued, not screwed. I may try the freeze board and try to pop off with razor blade method that seems to work well on epoxied HS's if they don't seem to want to budge.

[flocko]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Heat sinks are held with silicone and should come off if cut and twisted, all Q numbered parts are IGBTs and are tested for shorts with DMM set to low OHMs should read OL on meter if good between any combo of legs and tab,but will read low OHMs if shorted. all D numbered parts are Diodes and can be tested in diode mode with DMM most SMD diodes are tested legs to tab , and will read only one way if good, open or short if faulty, The R marked parts are resistors and should read the value marked on them out of circuit, I hope this is of help Flocko

[Terryfictv]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

After removal of shorted Q's or D's, check resistors in circuit.All R's
should be good! Only if they are open ( bad ) then replace.I have
not found it necessary to replace any R's yet !

[MTWallet]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Thank you flocko and Terry, I went ahead and hot air removed all the Q's and D's last night. I will test them and hold on to any that are good for future spares. The heatsinks were silicone blobbed and also thermal taped, so after razoring the silicone away from the side of the heatsink, they twisted off without a fight. I tested the R's afterward and they all read 7.6 Ohm, which should be about right as the replacements show to be 7.5 Ohm. Will get the solder pads cleaned up tonight and hopefully get the new parts installed and see how it works!

[flocko]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Just make sure to get the solder on the tab flowing. I use an old 80w iron with a bent screwdriver type bit and tin the backs (tab)of the new IGBTs and diodes ,heat the pad till the solder flows then slide the SMD in to place remove the iron, I do not trust hot air and low temp solder paste ,seen a few were they look to be on Ok but have high ohms between tab and pad. Flocko

[Terryfictv]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Did you note which parts go where? Also, the total count of parts in
SJ kit info is different than your count......you may not have the right kit !
Make sure you match part number & location. No subs....

[MTWallet]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Kit had the right number of parts for my board. 6 transistors and 2 diodes with 6 resistors. The shopjimmy site shows that kit in the search, but when you put it in the cart, it is the kit for the v2 board, which is what I have. Got everything put back on the board last night, but didn't get it in the TV yet. No short at SC2 anymore and everything at those R & D locations ohm out as they should. I.E. the tabs of each group of R's & D's show 0 ohm to each other, and the legs that lead to the resistors have 0 ohms as well. Also the other leg on one set of R's & D's shows 0 ohm to the long series of solder stripes, and the other set R & D show 0 ohm on the second leg to the small dots of solder, but not the strips. I checked these all from the pads with nothing installed before I started yesterday, so I'm confident that everything is in place as it should be with nothing shorted from my re-install of the parts.

Anywhere else I should check before firing it up?

[tw2005]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Always good practice to check the SD/Su boards too just in case they're shorted. In most cases thy're ok but should never assume. Can be caught out by it and blow another SC

[MTWallet]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

tw2005, thank you for your reply. I searched for about an hour last night looking for your info on testing shorted SD/SU boards. I found a post where you had posted a photo of an SD board showing to test at connector SD42. The points were labeled VFO, VSCN_F and VF5V, also showed to point VFG (GND). Is this the test your are talking about? Do I test the same points on the other two white connectors (SD46 and SU41)?

[Terryfictv]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Locate Panasonic Training Manual TC-P2012T1....
It has all the details.

[MTWallet]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Thank you Terryfictv, but neither google nor the site search helped me with those terms.

I did find a troubleshooting guide for 2012 TC-P50ST50's that seems to run down the same as what tw2005 posted as shown below. I think this is the same info.

tw2005, I think I finally found your post for isolation test and buffer checking. Is this it?

https://www.badcaps.net/forum/showpo...5&postcount=11

[tw2005]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

Thank you Terryfictv, but neither google nor the site search helped me with those terms.

I did find a troubleshooting guide for 2012 TC-P50ST50's that seems to run down the same as what tw2005 posted as shown below. I think this is the same info.

tw2005, I think I finally found your post for isolation test and buffer checking. Is this it?

https://www.badcaps.net/forum/showpo...5&postcount=11

give that a go or like I suggest if you set the meter to diode or continuity , place one probe on the earth plate on the buffer and then slowly slide the other across the face of the panel ribbon connectors making contact with each individual pin and watch for shorts. there's a VT30 post and he has shorted Su and the boards are almost the same as the St30 so it's worth checking these to be sure. In fact it's an important check, I've been caught on the 2010 models where the buffers usually survive but had one that sd/su and sc all shorted, put a new SC in and blew it up because I assumed the buffers would be ok.

[Terryfictv]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

See attachment

[MTWallet]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

give that a go or like I suggest if you set the meter to diode or continuity , place one probe on the earth plate on the buffer and then slowly slide the other across the face of the panel ribbon connectors making contact with each individual pin and watch for shorts

Oye! So you are talking about the copper colored ribbon cables that wrap around and connect to the SU/SD boards on the very left edge? If that's the case, I was totally not reading what you were saying right.

[MTWallet]

Re: Panasonic TC-P55ST30 SNAFU'ed, SC board blown, I think...

See attachment

Thank you kindly. I have been using this one, not sure if it is hiding here on the forums somewhere or not.