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Hi all, I have recently been given a non-working 42" Panasonic plasma TV model number TH-42PA60A. I have been informed that the power supply is faulty, and when I turn on the TV the screen comes on for a moment (and shows the OSD and everything seems ok) but then the relays click and the screen turns off after a few seconds. The longer you have the TV off, it seems, the longer the TV works before failing (up to a point, though). The red power LED flashes six times after the fault occurs (and keeps repeating the six flashes).
Upon inspection I found my power supply board to be a TNPA3911 part, but I do not know what revision number, if any.
Through my research, I found that this is a pretty common problem, with the board's replacement a probable fix, but since I was given this TV, and I don't really need it, I was not looking to spend the 150$ or so for the new board, which may end up failing in the same way.
More research showed me that Ebay sellers are offing repair kits for this type of power supply, consisting of a 10Ω 5W resistor, 8A fuse and the FS25SM power MOSFET (Nch) that is located at Q406. I went ahead and removed these parts, testing them to see if they were ok (since they are apparently at fault, hence the repair kit).
Everything tested fine, except I'm not sure about the MOSFET. I tried testing it according to the crude method found here: MOSFET testing. But I could not get it to work the way I expected (I have done this test before and know how it *should* work, but I think the MOSFET requires a higher voltage for turn-on, and thats why it didn't work).
Figuring I could sacrifice a lower spec'd N-channel MOSFET and see what happens, I removed the original part and replaced it with a RFP50N06 Nch 50A part that I had (but it has a much lower voltage). I tuned on the TV and it tripped my RCD, so no luck there. Now that I have substituted the old part back in, though, the TV does not turn on briefly like it used to, just flashed a sequence of ten flashes from the power led (it used to be six). (I also checked all the fuses to make sure they hadn't blown when the RCD tripped)
So, I wonder what's going on, and I hope someone can help me fix it up.
By the way, I also thoroughly checked for apparent capacitor problems as well as all fuses, any obvious overheating, damaged parts, cracked solder joints etc. I also have access to a scope and decent multimeter, just let me know what you think I should try.
Thanks everyone.
Upon inspection I found my power supply board to be a TNPA3911 part, but I do not know what revision number, if any.
Through my research, I found that this is a pretty common problem, with the board's replacement a probable fix, but since I was given this TV, and I don't really need it, I was not looking to spend the 150$ or so for the new board, which may end up failing in the same way.
More research showed me that Ebay sellers are offing repair kits for this type of power supply, consisting of a 10Ω 5W resistor, 8A fuse and the FS25SM power MOSFET (Nch) that is located at Q406. I went ahead and removed these parts, testing them to see if they were ok (since they are apparently at fault, hence the repair kit).
Everything tested fine, except I'm not sure about the MOSFET. I tried testing it according to the crude method found here: MOSFET testing. But I could not get it to work the way I expected (I have done this test before and know how it *should* work, but I think the MOSFET requires a higher voltage for turn-on, and thats why it didn't work).
Figuring I could sacrifice a lower spec'd N-channel MOSFET and see what happens, I removed the original part and replaced it with a RFP50N06 Nch 50A part that I had (but it has a much lower voltage). I tuned on the TV and it tripped my RCD, so no luck there. Now that I have substituted the old part back in, though, the TV does not turn on briefly like it used to, just flashed a sequence of ten flashes from the power led (it used to be six). (I also checked all the fuses to make sure they hadn't blown when the RCD tripped)
So, I wonder what's going on, and I hope someone can help me fix it up.
By the way, I also thoroughly checked for apparent capacitor problems as well as all fuses, any obvious overheating, damaged parts, cracked solder joints etc. I also have access to a scope and decent multimeter, just let me know what you think I should try.
Thanks everyone.
