Pioneer PDP-502MXE 50" 720p plasma Faulty PSU

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  • SchrodingersCat
    Member
    • May 2010
    • 43
    #1

    Pioneer PDP-502MXE 50" 720p plasma Faulty PSU

    Hi!

    I recently picked up one of these TVs 2nd hand for next to nothing in the hope of repairing it. The described symptoms were a "clicking noise, but no power" when the TV was plugged in.

    After getting the massive 50" TV home, I opened it up, and was delighted to see some very high-quality components inside compared to the other cheap and cheerful TV's that I have opened in the past. I had a read of tom66s thread here of the same TV with similar symptoms. He ended up repairing the TV by replacing the large FET and one of the power resistors on the primary side of the PSU. Sure enough, when I tested the Q281 MOSFET (Toshiba K2847 .9G , see attached image), it as shorted from Gate <=> Drain and was visibly damaged, and the resistor R134 (2.2 ohm, 7w ) was open circuit (both circled in one of the attached images). This resistor is in series with two other similarly rated resistors. I sourced three Toshiba K2847 .432 and four CGS SBCHE6 2R2 K SW JL power resistors (some for spares) from ebay. I replaced both on the board, having to mount the power resistor on its side as it was higher than the cover would allow.


    I powered up the TV and it was unresponsive. Then I noticed that the kettle lead that I had used had its 5amp fuse blown. As the internal fuse was a 10A HRC fuse, and it was such a large TV, I assumed that I would have to replace it with a 13 amp fuse, which I did so. I powered up the TV again, and this time I got four clicks from the relays, and after the last relay click, LED D407 lights on the PSU. The standby light continuously flashes, but the TV is unresponsive and does not power up.

    I checked the components again and noticed that the MOSFET that I had just replaced had shorted again, taking the third power resistor in the series with it (it was not open circuit). :-(

    There are three Toshiba MOSFETS on the primary labeled "K2847 .96", and the replacement MOSFET that I used was differently labeled "K2847 .432". From the spec sheet (see attached), this appears to be just a "lot number" so am I correct in assuming that this should be a correct replacement?

    I have a two spare Toshiba K2847 MOSFETS and three power resistors, but I am wary in replacing them now before I can track down the issue. I had to source them from Malaysia and would hate to have to pay and wait again if I was they just blew again. I assume that there is a short somewhere else down the line that is causing the MOSFET to short and blow the incoming power resistor. Would anybody how I would go about tracking it down?


    Thanks in advance! :-)
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    • tom66
      EVs Rule
      • Apr 2011
      • 32560
      • UK
      #2
      Re: Pioneer PDP-502MXE 50" 720p plasma Faulty PSU

      Those little vertical boards next to the FETs? Those can sometimes be damaged by the FET failure. Luckily all three are identical, so you can use one to compare against. You'll need to identify any possible failures on that board.
      Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
      For service manual, schematic, boardview (board view), datasheet, cad - use our search.

        Comment

        • SchrodingersCat
          Member
          • May 2010
          • 43
          #3
          Re: Pioneer PDP-502MXE 50" 720p plasma Faulty PSU

          Thanks for the response tom66! Im grateful for your help.
          Sure enough, when I removed the three RCC Controller A, B & C boards and compared them against each other, I found some faults with board A. This happens to be the board that is connected to the gate of Q201, the original large MOSFET that blew taking the power resistor R134 with it.

          On the RCC Controller A board I found that resistor R232 (2.2 ohm) was blown. There was a short between the base and emitter of Q208 (markings "D1835 S 0B", looks like to be a standard NPN transistor ). There was also a short between pin 1,4 and 6 of IC203 (markings 5233 034, not sure what this is yet, it could be a PITA to find a replacement).

          I came across this trouble shooting guide for the power supple board here: dafpolo.free.fr/telecharger/plasma/schema_plasma_pioneer.pdf

          This suggests that aswell as IC203, Q208, and R232, that I also test D224 and D226. However, I found these diodes to be pretty much consistent across the three boards, and so probably working fine.

          So, the plan of action is as follows:
          (Unless anyone has any better ideas). Replace the resistor R232 and see if I have a NPN transistor somewhere to replace Q208. While the NPN transistor is removed, I will test IC203 to make sure that its not causing the short across the IC.

          Finally, if I am happy with the repairs made to the RCC controller board, I will put the three of them back in the PSU board. Then I will replace the large power resistor that burnt out, but I will leave the large Q201 MOSFET out of the board. I will borrow an oscilloscope and see if i can see a some kind of satisfactory control signal from the repaired RCC Controller Board on the pad where the gate of the MOSFET should be (I can compare the signal to the gates of the other two MOSFETS immediately after I power the thing up). Finally, If I am happy, I will solder the MOSFET back onto the board, put a low 5amp fuse into the plug, and power up the TV hoping not to blow any other expensive or hard to source components.

          Wish me luck!
          Last edited by SchrodingersCat; 04-20-2013, 09:39 AM. Reason: typos

            Comment

            • tom66
              EVs Rule
              • Apr 2011
              • 32560
              • UK
              #4
              Re: Pioneer PDP-502MXE 50" 720p plasma Faulty PSU

              Service manual:
              http://www.tgohome.com/ServiceManual...&Search=Submit

              The IC203 I think is a dual opamp.
              Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
              For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                Comment

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