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Panasonic TH-42PX80U Repair Adventure

post #1 of 5
Thread Starter 
Background: I am an electronic hobbiest, not a technical repair person like TWiz. Therefore, the following procedures will not be proper in a professional environment, and may involve risk.

Panasonic TH-42PX80U Service Manual
Panasonic TH-42PX80U Technical Guide

A couple of years ago, I was able to inexpensively obtain a Panasonic TH-42PX80U plasma set with a broken plasma screen. Those 11th generation 2008 models were highly available with broken plasma screens because of shipping mishaps. My hope was to find another inexpensive TH-42PX80U with an intact plasma screen but with circuit board problems, and I would just swap the boards out between the two sets and have a cheap working plasma.

Well, a couple of weeks ago I found a TH-42PX80UA that the owner said a lightning strike had caused a surge and fried one of the boards. A repair shop said the A-Board was bad and would cost $500 to replace. The owner decided this was too much and purchased a new plasma, thus this broken one was available inexpensively.

When I inspected the TV, it would turn on with a solid LED indicator, and the plasma screen would light up, but the OSD (On Screen Display) did not work. Seeing the plasma screen itself was intact and working, I figured replacing some of the boards from my other broken-screen TV would produce a working plasma.

So, thus begins the tale of creating a working plasma.

The first step was to remove all of the screws on the back cover. There seems to be an excessive number of screws, but probably necessary when you take off the back and realize how flimsy it is.

Panasonic was thoughtful in providing hanging posts for the back cover, so it would not fall off when removing the screws.

After the back cover is off, the next step was to remove the A-Board cover. Notice that the HDMI screws have to be removed also.

Next, the connectors and ribbon cables needed to be uninstalled from the A-Board, and then the grounding screws removed for board removal.

With the replacement A-Board installed, the TV was tried out.

Uh-oh, the LED indicator was now flashing 7 blinks and inoperative. According to the service manual and technical documents, the 7 blinks indicated a bad SC, SU, or SD board. Using the information provided in the above manuals, I was able to isolate the SU and SD boards, and determine that the SC-board appeared bad. Next step was to remove the bad SC-board.

Uh-oh again! When comparing the size of the replacement SC-board, it was larger!! The replacement board on the left was from my broken-screen TH-42PX80U, but the bad SC board on the right was from my intact-screen TH-42PX80UA.

Got it? Panasonic, in their wisdom, had produced a modified model for the 2008s around Sept 2008, and designated them with an "A" suffix. And they use different boards. This apparently also happened with the 10th generation 2007 models.

So, I had to modify something to get the larger SC-board installed. The grounding posts on the plasma screen aluminum heatsink were not removable, so without insulation those existing posts would touch the larger replacement SC board and short out something.

I temporarily installed a paper sheet to act as an insulator, and test-fitted the new board to see if the posts where insulated.

Next, since the board could not be fully mounted on those misaligned posts for grounding purposes, I had to ground each grounding point with wired aligator clips after the board was installed with screws.

Fired up the TV, and it worked great! OSD was available, and no LED blinks!!

Now, to permanently mount the SC board. As an insulator, I tried to use stiff plastic, but it was not flexible enough. So instead I used heavy vinyl shelf liner.

I had to ground those grounding points that could not be mated with a post. Bell wire and bolts/washers/nuts were used to provide a ground loop, and a terminal to affix to a grounding point on the aluminum chassis.

The SC board permanently installed.

Tested the TV once again, to be sure it still worked. Then installed the A-Board cover, and the back cover. The TV has been working great this past week!

One note: Because of using the A-Board from the TH-42PX80U, it may not have been compatible with the SC-Board from the TH-42PX80UA. Once the SC-Board from the TH-42PX80U was used, compatibility between the boards existed. The SU and SD boards from both sets are equivalent.

Final thoughts ... when buying any boards from eBay, try to determine if it came from an earlier unit or a later "A" unit. They are not compatible!
post #2 of 5
I love happy endings. Good job.
post #3 of 5
This is actually a pretty cool repair.

It does show a few good points:

1.) It is nearly essential to have the service documentation.
2.) Models versions with a suffix ("A") are probably different in some manner.
3.) The mounting holes need to be screwed into the chassis for grounding.
4.) Some basic troubleshooting aptitude is needed by the DIY, as this poster has shown, not just to come to the forum looking for step-by-step Kreskin type instructions.

BTW, you are correct. We might test with the wire-grounded different board just to get it to fire up but would order the correct board to complete the repair.

Congrats on a successful outcome.

T Wiz
post #4 of 5
Thread Starter 
Thanks, tfoltz and TWiz for the kind comments.

Keeping TWiz's comment in mind about obtaining the correct board to complete the repair, I recently found a TH-42PX80UA with a broken plasma screen on eBay for $50.

I removed the A-board and SC-board from that broken TV, and installed them into the working intact TV after removing the rigged boards. I now have a perfectly working TV with the correct boards for a total of $110 ($60 for the intact screen TV off Craigslist, and $50 for the eBay parts TV).

I really like the TH-42PX80UA. There were thousands sold, which makes parts readily available. Although only 720p, it has great color and resolution. It has the anti-reflective screen, analog audio output, uses few boards, simple to repair, and very energy efficient.

And, it may be one of Panasonic's most reliable plasma models because of its simplicity. Most failures are due to mishandling (cracked screens) or electrical surges (by not using surge protectors), and not a fault of the actual TV.
post #5 of 5
How you never blew your house up as a kid is beyond me. Good job
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