A "Thank You", and some tips on repairing Panasonic Plasma TVs

[volleyrca]

Hey all,

I have a Panasonic TH-42PZ700U, which worked great for 10 years until a few months ago when it died with the, apparently common, 7 blinks failure. While I wish I had known about that problem, and the firmware upgrade that is supposed to prevent it from recurring, I'm happy to report that I was able to successfully repair my TV based on the information in the "Panasonic TH-42PZ77U SC board repair 7 blinks" thread on this forum, and in the "Master thread for Panasonic plasma not turning on" thread on AVSforums, in particular post 536.

I didn't want to revive a thread that has been cold for over a year, but I wanted to share a quick recap and a couple tips and advice I picked up in the process...

• The TV is a Th-42PZ700U, which is about 10 years old, and it failed with 7 blinks.
• Following Service Hint SH-B34-08-03 I disconnected the SD and SU boards from the SC board and still got 7 blinks, but when I unplugged the SC board (connectors SC2 and SC20) the power LED was solid red when the TV turned on
• I removed the SC board and followed the instructions from the linked AVSforums thread (also included in the 7-blinks thread on this forum) to test the FETs. Sure enough three were failed ones from the same group where that poster found a failed FET
• I ordered replacements from Encompass, the official Panasonic parts supplier, but despite showing as "In Stock" they were actually back ordered. It took two weeks to get 1. Meanwhile, I ordered some "5N2307" parts from a Chinese supplier on Amazon, and from Aliexpress (there was virtually no other useful information in the product descriptions), and they all arrived around the same time.
• The replacements all had very similar markings, and similar resistance measurements, so I picked two of the ones from Aliexpress to install along with the OEM one.
• It was tricky both to remove the failed FETs and properly solder the replacements. Here's what helped:
  • pre-heat the board (safely) -- I was able to use a hot-air pre-heater from Zephyrtronics (which some friends own), which we placed under the board, but a helper using a heat gun from a safe distance could probably be OK
  • Desolder both legs of the FET first
  • Apply some solder to the metal tab on the back of the FET where you're placing the tip of the soldering iron to help with heat transfer
  • If there's not much solder on the pads on the board (there wasn't on mine), tin them very lightly (you still want the pad to be very flat for installing the replacements), liquid flux is helpful to use for this, too
  • Have a friend help with installing the replacement FETs - I positioned the FET and pressed down on it with tweezers while my friend used a soldering gun to heat the metal tab (with some solder between the tip of the gun and the tab, as for removal). When the solder on the pad melted we could see it flow out to the edges of the FET. After getting the back of the FET soldered on, then solder the legs
• Some tips for what I think is the best way to reconnect the SD and SU boards to the SC board:
  • Have a friend help, an extra pair of hands will make it easier to connect the second board to the SC board after the first one is connected
  • Remove the long, thin metal bracket that runs horizontally and attaches with three screws to the top of the metal housing around the A/V connections
  • Remove the the housing holding the fans above the top of the SC board (or at least remove the leftmost, upper left, and upper right screws, and loosen the rightmost screw, so it can be easily moved
  • Remove all the small white ribbon connecting the SD and SU boards to each other if you haven't already (I did this when disconnecting them from the SC board)
  • Working on the SD/SU boards one at a time, remove all the screws from the SD/SU board so that with the ribbons still connected it can rotate to be perpendicular to the plasma display. Then, from the underside of the SD/SU board and SC board you can mate the card edge connectors applying pressure to the edge of the SD/SU board where the ribbon connectors insert, and to the SC board using the nickel-sized circular holes at the top/bottom of the board
  • Rotate the connected SD/SU and SC boards back into place (this is where having the fans and metal bracket out of the way is necessary). There is just enough slack in the ribbon cables to do this
  • Why I did it this way and what not to do: I actually ended up reinstalling the repaired SC board, removing it to check something, and then reinstalling it again. On the first reinstall I found it was very difficult to reconnect it with the SD and SU boards, because the ribbon cables connecting the SD and SU boards to the plasma panel don't leave much space where one can press on the edges of those boards from the front side, and I didn't feel that I could apply enough force to get the card-edge style connectors to mate without the risk of damaging the ribbon cables/connectors or other components. At first I chose to disconnect the ribbon cables, but it's rather tricky to get them reconnected properly, and if not connected properly there will be black horizontal lines running across the display. The second time I reinstalled it as described above.
• If for some reason you do need to disconnect the ribbon cables, what I found helpful to reconnect them properly was:
  • Carefully push the ribbon all the way in to the connector, and then carefully apply pressure to the curved area of the ribbon with a credit card and to the edges where it widens near the end inserting into the connector, and then very slowly close the connector, to prevent the ribbon from being pushed out as it closes.
  • Also, I made a test pattern to show on the TV (hooking it to my laptop with an HDMI cable), that had 8 equally-sized 135-pixel-tall horizontal stripes, and at the top and bottom of each stripe were 2-pixel tall stripes that were different colors from each other. This let me accurately see which ribbon cables were not properly connected so I could work through them one at a time, and not unnecessarily disconnect any that were connected properly
• Install the firmware upgrade right away

Thanks again to the posters on this forum (and the 7-blinks thread) for providing so much of the info that made it possible for me to make a successful repair.