SX-626. The trials and tribulations of troubleshooting when you hardly know what your doing.

Discussion in 'Pioneer Audio' started by kaplang, Dec 31, 2018.

  1. kaplang

    kaplang Works for me ! Subscriber

    Let me start out by saying that my troubleshooting and schematic reading skills are marginal at best. That being said here is what i think I need to know to try and get the Pioneer SX-626 working again. Or at least a starting point

    The main amp unit AWH - 002 has several pins connected to ground that include E1,E2, E3 and E4 if I am understanding the schematic correctly. I currently have everything disconnected from the board except for +B of 56 volts DC to pin B1, B2 and pin E5 to ground. With only these 3 connections the 4 pins E1,E2,E3 and E4 are all showing a reading of 56 volts DC and that makes no sense to me since those are suppose to be ground connected. I have tested every component on the amp board out of circuit and have found nothing that explains why 56 DC volt readings are showing on pins to be grounded.

    Anybody want to jump in here give me some help. It will be greatly appreciated and who knows, I’ll probably learn a few things

    Cheers and Happy New Year
    George

    Main amp unit AWH-002
    30BEF1FA-B23F-47FA-BC0B-0AA057A7BE48.jpeg 34DAFC09-AEB7-4AC8-8C84-75385A011EE9.jpeg 92E2D71C-67BE-4B51-A48F-84827C1CF6B3.jpeg
     

     

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  2. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
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    Location:
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    If they are supposed to be connected to ground and they are not they will be pulled up to 56v (or whatever voltage they are connected to). The schematic plainly shows they are not interconnected on the board, so they MUST be grounded by their external connection. When no current flows to cause voltage drops everything sits at the highest potential, just like a bird on a power line.
     
  3. UncleBingo

    UncleBingo AK Subscriber Subscriber

    Messages:
    1,819
    What were the symptoms before you pulled the amp board? Troubleshooting these is way easier if you leave stuff connected. Also, some components can test "Okay" on a simple meter, and still be far from okay. Caps and transistors, for example.
     
  4. kaplang

    kaplang Works for me ! Subscriber

    The symptoms were no output right channel and outputs on left channel would get very hot to touch. Problem has been resolved. Right channel had 1 shorted output transistor, a shorted PNP transistor and a baked resistor. Replacing those got the right channel back. The heating outputs on the left channel turned out to be an open on the pot that manages the bias setting. I cleaned it and the problem went away.

    I try to do all of my component readings out of circuit and along with owning a DMM I have an actual transistor tester and a capicator meter that I trust.
     
    Last edited: Jan 11, 2019
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  5. UncleBingo

    UncleBingo AK Subscriber Subscriber

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    Sweet! Good work. The usual suspects strike again.
     
  6. kaplang

    kaplang Works for me ! Subscriber

    I got a lot of help from some of the other usual suspects. Several AK members that got me to the point of repair and I thank them all.
     
    UncleBingo likes this.

     

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