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Old 09-06-2017, 08:52 PM   #1
mmischni
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Default Panasonic Viera Plasma TH-42PX75U 7 Blinks/8 Blinks/burned P board?

Greetings friends,

I have a Panasonic TH-42PX75U manufactured in 2007. It has been trouble-free until recently. One evening I turned it on and it then powered back off and gave 7 blinks.

First a question about the blinks. Everyone only speaks of a single number of blinks. I noticed on my TV, it blinks one fewer times for the first group of blinks, then blinks the full number repeatedly. So for my first code in question, the TV switches off, blinks 6, then blinks 7 repeatedly. When I disconnected the SC board, the TV switches off, blinks 7, then blinks 8 repeatedly. Is this how they usually behave and everyone just understands that? Just curious on this one. I have been troubleshooting assuming that the repeated number of blinks is the appropriate one!

With that out of the way, I repeatedly get into 7 blinks error code. I found and used the Panasonic Technical Guide/Troubleshooting handbook for my model of TV, starting on the page for 7 blinks (see 7Blinks image attached). This page indicates it could be SC, SU, SD, or P boards. However the flow chart led me to the SS board, because the TV does not stay powered up with SC disconnected (but I get 8 blinks then, instead of 7), 15V is on pin 1 of P25, and Vsus (195V for this TV) appears at pin 1 of P2.

I thought I was in good shape and ordered an SS board from ShopJimmy. The SS board swap did not change anything. I still get 7 blinks. I think now it is perhaps a used board (or refurb?) as it was only $24, packing seemed "used", and heatsink seemed more scratched than you would expect on a new. The listing made no mention of its status used or new, I was just assuming new. So I suppose I don't KNOW that the second board is good. Following the troubleshooting flow chart for 7 blinks with the new board installed leads me to the same place, replace SS board.

I am wondering about the flow chart, the defective board list for the 7 blink code (SS is not included on that list, but is on the flow chart), and the fact that I get 8 blinks with the SC board disconnected. This doesn't all work well in my mind and I wonder if multiple issues are at play, or if there is something I don't know (likely!) that is confusing me. There is an 8-blink troubleshooting procedure as well (see 8Blink image attached), but I don't know if it is appropriate to use this if I only get the 8 blinks when disconnecting the SC board. Following that procedure as written leads me to the D board. There are lots of instances online of apparent SC board failures (which the 7 blink code is apparently most often given for), and if I follow the 8-blink flow chart through to the end (answering NO to the middle diamond, even though I DO have Vsus voltage), and disconnect SC2 and SC20 with all the other changes made, including that jumper on P12, the TV powers on and stays on.

So it feels like the SC could be part of the problem, but I realize I am misusing the flow charts a bit and possibly projecting what I have read onto my TV. I would appreciate anyone who can give some advice on the symptoms and the somewhat basic troubleshooting I have here. I have attached some pics of the boards in the TV. Maybe that will help, but at this point, maybe the main faults are in how I am interpreting what I see, and that may not require pictures to set me straight...

Also in inspecting the boards, I noticed dark spots around D411 (a diode?) on the P board. I attached a close-up of that. I would have expected heat to be in the component, not around the leads. What do you make of this? Nothing in the flowcharts implicates the P-board. D411 appears to have about 8ohms in either direction. That doesn't seem very diode-y to me. As my disclaimer, I am a mechanical engineer who knows enough electronics to make my mechanical projects work. My DVM is a $6 Harbor Freight model, although I DO have access to better stuff at work.

Thanks for any re-direction or advice you can give!!

Matt
Attached Images
File Type: jpg 7Blinks.jpg (169.4 KB, 7 views)
File Type: jpg 8Blinks.jpg (212.9 KB, 5 views)
File Type: jpg Overall_Layout.JPG (1.47 MB, 12 views)
File Type: jpg SS_Board_Replacement.JPG (1.51 MB, 10 views)
File Type: jpg SC_Board.JPG (1.70 MB, 9 views)
File Type: jpg SU_Board.JPG (1.78 MB, 6 views)
File Type: jpg SD_Board.JPG (1.92 MB, 7 views)
File Type: jpg P_Board.JPG (1.46 MB, 9 views)
File Type: jpg P_Board_D411.JPG (1.19 MB, 14 views)

Last edited by mmischni; 09-06-2017 at 08:55 PM.. Reason: Add model name to title
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Old 09-07-2017, 05:20 AM   #2
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Default Re: Panasonic Viera Plasma TH-42PX75U 7 Blinks/8 Blinks/burned P board?

Remove the power board and look at the backside for bad solder joints. It might just be dust. Also test the diode.
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Old 09-07-2017, 08:11 PM   #3
mmischni
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Default Re: Panasonic Viera Plasma TH-42PX75U 7 Blinks/8 Blinks/burned P board?

The back of the board looks ok to me. Picture attached, back side of diode highlighted. I realized that I was probably testing the legs of that adjacent coil device rather than the diode. I removed the diode from the board and it tests open in both directions. It says T2D79 on the diode. A Google search of those numbers didn't show much promising. I did find some options using the Panasonic PN (B0BB17000009). Prices ranging from $10 to $25 for one diode. While this doesn't offend me too much if I get my TV back, it seems high for a single diode. What do YOU think?

EDIT - Continued searching led me to a discussion of a diode with a similar number (T2D93) and a tech on justanswer.com who stated that this diode is a config of two diodes back-to-back that would test open both ways, even if good. Does this sound like something that could be the case for me? Sounds like this config is used for snubbing, and this component being parallel to something that looks like a coil would jive with that. -END EDIT

Once it is replaced, I assume I will still be troubleshooting for any other faults it's death caused?

Thanks,
Matt
Attached Images
File Type: jpg P_board_D411_Back.jpg (276.2 KB, 13 views)

Last edited by mmischni; 09-07-2017 at 08:42 PM..
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Old 09-08-2017, 01:26 PM   #4
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Default Re: Panasonic Viera Plasma TH-42PX75U 7 Blinks/8 Blinks/burned P board?

Looks like a diode plus 170V zenner diode in series within one package.
http://www.elektroda.pl/rtvforum/topic1983642.html
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Last edited by dick_barton; 09-08-2017 at 01:31 PM..
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Old 09-08-2017, 06:09 PM   #5
mmischni
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Default Re: Panasonic Viera Plasma TH-42PX75U 7 Blinks/8 Blinks/burned P board?

So I should probably put that diode right back in, as my diode tester probably isn't the right tool to know anything about that diode.

Any thoughts on the rest of the issues and how they have worked out in the trouble shooting?

Thanks!

Matt
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Old 09-20-2017, 08:39 AM   #6
mmischni
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Default Re: Panasonic Viera Plasma TH-42PX75U 7 Blinks/8 Blinks/burned P board?

I know posting a second thread on the same issue is poor form, but I thought maybe I over-did it on details in my first post, and no one wanted to read it all. So I tried again with just the basics on a second thread.

Ultimately, the power board was a dead end. That diode was not testable with my equipment (and knowledge), and appears to be OK, despite the dark areas around the leads.

For posterity: The final solution, despite a few wrong directions, was a new D board and re-seating cables. See my other thread where I followed the successful path to repair!

https://www.badcaps.net/forum/showth...175#post772175

So long,

Matt
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