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Old 09-12-2017, 08:38 PM   #1
mmischni
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Default Panasonic Viera TH-42PX75U with 7 Blinks

Hello,

I have a Panasonic plasma born December 2007. It recently started giving the 7 blink error code. I followed the flow chart for 7 blinks (attached below) in the troubleshooting guide that I found for this model. With the SC board disconnected as indicated, the TV does not stay on, but instead gives an 8 blink code. I checked the specified voltages and both were present, indicating the SS board was the culprit. I tried a replacement SS board from ShopJimmy, but the problem was the same. A different SC board swap also yielded no difference.

When the SC board is connected, 7 blinks. When it is disconnected, 8 blinks.

Any ideas of other checks I could do?

Thanks,
Matt
Attached Images
File Type: jpg 7Blinks.jpg (169.4 KB, 15 views)
File Type: jpg Overall_Layout.JPG (1.47 MB, 15 views)
File Type: jpg SS_Board_Replacement.JPG (1.51 MB, 14 views)
File Type: jpg SC_Board.JPG (1.70 MB, 15 views)
File Type: jpg SU_Board.JPG (1.78 MB, 10 views)
File Type: jpg SD_Board.JPG (1.92 MB, 13 views)
File Type: jpg P_Board.JPG (1.46 MB, 11 views)
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Old 09-13-2017, 01:53 AM   #2
Moreno83
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Default Re: Panasonic Viera TH-42PX75U with 7 Blinks

Take your multimeter , put it in DC range. Put the propes on the upper left connector of the powerboard , i think it will read something like P22. Its the connector that goes to the SC board. What voltage do you read?

Also try the following , meter in continuity and put both pins on the SC2 connector of the SC board , do you get a beep? It is ok if it beeps for 2/3 seconds. Longer beep is not good.
Usually the SC ( ysus ) fails on these plasma tv's. ( or buffer ).
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Old 09-13-2017, 05:47 AM   #3
mmischni
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Default Re: Panasonic Viera TH-42PX75U with 7 Blinks

Hi. The upper left connector on the power board is P2. It goes to 195V before the TV shuts off. Vsus is supposed to be 194V according to the sticker in the TV. Continuity test at the SC2 connector flashes around 150ohms, then goes to "out of range" so it doesn't seem to be shorted at that point at least.

I agree the SC sounded like a common failure, and that is one reason I replaced it when replacing the SS did not help. But the troubleshooting guide makes it sound like if the SC is faulty (or the buffers, SU/SD), disconnecting the SC should let the TV stay running. But I get a shutdown and 8 blinks after that. Maybe there are multiple failures? Or the diagnosis circuitry is being fooled by an unusual fault?

Thanks again!
Matt
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Old 09-13-2017, 08:45 AM   #4
Moreno83
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Default Re: Panasonic Viera TH-42PX75U with 7 Blinks

Ok so the powersupply works , thats good. 195V is good.

If the tv does not run without the buffers then there is a good chance the sc board is faulty. Especially with the long beep you are measuring.
There are some parts on that SC board that are soldered ( and screwed ) to the heatsinks.
They are labeled with "Q" and the parts are mosfets. Measure those components continuity/diode mode. Put the propes on the outer legs. Beep is bad.
If you find 1 or 2 ( usually more ) of these then your sc board is bad.

I cant find the part number on the board , its probably hidden under the buffer boards.
Google that part number with repair kit. "TNPA56... repair kit" and see if you find the components that are usually short on this board so you can measure them.
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Old 09-13-2017, 07:07 PM   #5
mmischni
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Default Re: Panasonic Viera TH-42PX75U with 7 Blinks

Thanks for helping out.
So the TV does not run with the SC board disconnected (two connectors, 1 power and 1 ribbon). I assume that means the buffers are also then disconnected, as they only seem to be connected to the rest of the system through the SC board. Does it tell me something to remove the buffers and turn it on with the SC connected and the buffers removed?

I tested all the Q components across the outer legs and none are shorted. Some have values in the 1800 range (is that ohms in the diode mode?), some have lower values like 600s, or 250s. None appear to be dead short. There are some similar components labeled with D that have continuity across the outer legs. These helped convince me to try a new SC board, but maybe they are supposed to be this way. Components on both boards, old and new, measure about the same.

The number on the SC board is TNPA4182. I didn't find any repair kits for this immediately available (meaning I only looked a couple pages deep in Google...)

Thanks,
Matt
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Old 09-15-2017, 08:01 PM   #6
mmischni
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Default Re: Panasonic Viera TH-42PX75U with 7 Blinks

So how about this? Once I disconnect the SC board, I get 8 blinks. If I use the troubleshooting flowchart for 8 blinks (attached), it leads me to the D board. TV still shuts down with the SS connectors and power connector removed and a jumper on P12. The Vsus voltage exists at pin 1 of P11.

What do the experienced troubleshooters think about the likelihood of a faulty D board being the root cause? It seems that something about this fault may be causing the TV to report a code that doesn't jive with the standard troubleshooting wisdom...
  • I think the power board is OK as power is always where it is indicated that it should be.
  • New/different SS board and new SC board do not fix or change the problem.
  • Disconnecting the SC board (and by extension the buffers?) does not let the TV stay running, so I THINK the buffers may not be the likely cause...

Thanks!

Matt
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File Type: jpg 8Blinks.jpg (212.9 KB, 7 views)
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Old 09-17-2017, 06:22 PM   #7
mmischni
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Default Re: Panasonic Viera TH-42PX75U with 7 Blinks

Any other ideas for me?

Is the D board the location of the on-board diagnostic circuitry? If so, maybe that would jive with what I am seeing. A fault on the D board maybe causing inaccurate blink codes, or otherwise confounding the diagnosis the TV gives. Maybe.

Thanks,
Matt

Last edited by mmischni; 09-17-2017 at 06:34 PM..
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Old 09-19-2017, 10:27 AM   #8
mmischni
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Default Re: Panasonic Viera TH-42PX75U with 7 Blinks

Looks like the D board handles the following processes:
  • Format Converter
  • Plasma AI
  • Sub-Field Processor
Unfortunately I don't know exactly what those processes are. Do any of these sound like they would include on-board diagnostics? Only Board A with the microcomputer sounds like another possibility.

Thanks!
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File Type: jpg Panasonic Board Layout.jpg (201.6 KB, 9 views)
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Old 09-20-2017, 08:33 AM   #9
mmischni
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Default Re: Panasonic Viera TH-42PX75U with 7 Blinks

A replacement D board was available for $24 from ShopJimmy, so I ordered one. Installing that gave me 6 blinks! Now I was getting somewhere. Using the 6 blink trouble shooting, it led me to re-seating connectors between the D and C boards, and between the two C boards. Believe it or not, that got things running. Ran it for 1.5 hours last night with no issues.

So for posterity, a new D board and re-seating connectors was the ultimate fix for my 7 blink code. It could be that the faulty D-board was confounding the on board diagnostics, I am really not sure.

The initial 7 blink code caused me to buy an SS board that I did not need, and reading the forums caused me to buy and SC board I did not need (I followed the trouble shooting flowchart, but didn't listen to what it told me because the SC board seemed like a common fault, and I was measuring the wrong transistors!). When I decided to do what the flowchart indicated, I got there in the end. I'll get some money back for the returnable SC, and I have a spare SS should I need it. And I didn't spend a few hundred to get it diagnosed/repaired. And I don't have to buy a new TV and figure out how to connect all my old devices on these new TVs with so few legacy inputs!

Seems like an uncommon failure, but maybe this record will help someone else some day. Hopefully this plasma will last a few more years until the OLEDs come down a bit more in price.

Matt
Attached Images
File Type: jpg 6Blinks_1.jpg (354.3 KB, 13 views)
File Type: jpg 6Blinks_2.jpg (212.6 KB, 12 views)

Last edited by mmischni; 09-20-2017 at 08:34 AM.. Reason: Forgot to attach 6-blink diagnostic
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