Panasonic TC-P42X3 PSU Repair

[NosukeX]

Hello all. I have been trying to fix this TV that I purchased, and it has been nothing but a headache. The original symptoms were no power at all to the set. I used the Panasonic Training Guide combined with the service manual, as well as various posts from this forum concerning similar models to determine that the A Board was at fault. I sent the A board to ModusLink for repair, and when I reinstalled it, the relays starting clicking and I tried to power on the set. The TV went into locked mode with 14 blinks, which indicated either the P or A board was at fault.

Initially, I could not find any defects on the P board, so I went looking at the SN and SS boards and concluded that the SN board was shorted, so I purchased replacement boards for both. Those didn't work either, so I examined the P board once more and found that 2 diodes were broken, and one was shorted out. Now that I have found a real issue, my question is: How do I determine what kind of diodes to order? I have attached pictures of the board in question. D525 and D528 were broken, and D104 is the one that is shorted.

[CapLeaker]

Re: Panasonic TC-P42X3 PSU Repair

maybe these diodes have a number written on them?

[NosukeX]

Re: Panasonic TC-P42X3 PSU Repair

The reddish orange diodes do not have anything printed on them. The black one does but I've not unsoldered it to check at the moment. The only thing I see on the glass ones are a yellow stripe near the cathode. Extensive research has me thinking that they are silicon standard signal diodes, but I remain unsure. When using my DMM in diode mode, I get a reading of about 560, which I translate to be 0.56V, or the expected value of a silicon diode as read through a cheap multimeter. I just wanted to know if I could simply go to the RadioShack in town and find a suitable replacement, or do I need to special order the diodes in question. I admit that I have been "learning as I go" with regards to the few TVs I've repaired. The power board in question is a MPF6907. I have the schematics for it, but they haven't been much help. I have uploaded it in case anyone has any more information that could be of use.

[vinceroger69]

Re: Panasonic TC-P42X3 PSU Repair

The black diode maybe ok when removed and tested some diodes do read shorted on the board bur are ok with one side lifted and tested.

[NosukeX]

Re: Panasonic TC-P42X3 PSU Repair

Just an update: After searching for hours looking for the part number of the 2 broken diodes, I stumbled across information indicating that were simply Panasonic brand switching diodes. So, today I went by RadioShack and picked up a pack of 1N4148 diodes and soldered them in, and for the first time ever, I saw the TV come to life!! After working on this TV for a month, it was quite a relieving moment. So far, the set is working fine.

For anyone who has this TV, I located a substitute for the impossible to find SN board, PN# TNPA5311AC. Rather than send my old board in to ModusLink, I opted to try PN#TNPA5311AE, normally found in a Sanyo DP42740, as the boards looked almost identical. I'm happy to report that the AE revision worked wonderfully. It also happened to be $70 USD cheaper as well. Thanks for the help people, I'm sure to be back soon when I acquire my next TV.