What did I do to fix my SX838??

Discussion in 'Pioneer Audio' started by Bill S, Feb 7, 2019.

  1. Bill S

    Bill S Thread Killer Subscriber

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    I've documented my issues with my SX838 here: http://www.audiokarma.org/forums/index.php?threads/another-sx838-help-thread.852969/

    Unit was still going into protection after replacing Q7, Q6 on protection board but it held for a few minutes before tripping. I left it for a day and today, I turned it upside down, powered it on and timed how long it would stay lit. Well, I'm at about 45 min and it's still playing at 1/4 volume. I do notice some discoloration (heat) on the PS board. The large R3 resistor measures 91C right now and Q1 right next to it is at 62C measured at the base of the heat sink. Q2 on the other side, further away from that resistor measures 54C at the same location. Any ideas as to whether this might be related to the protection problem? I'm thinking that with it upside down, the heat is dissipating better. Is replacing Q1 & Q2 as well as the resistor the solution here?
     
    Last edited: Feb 7, 2019

     

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  2. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Rebuild the power supply board.Correct voltages off the P.S. board will lessen your problems down the road with the other boards. PIONEER did these units(SX838-939-1010) a big dis-service when they built them with the P.S. UPSIDE DOWN on the bottom of the unit. No place for the heat to go. Replace the Q's with upgraded parts in the parts list elsewhere, and get some small finned heatsinks and add to the heatsink plate on the P.S.
    Replace resistors as noted in the parts list and raise them off the board 1/4" to 1/2" to get airflow around them. And install NEW 105*C rated Caps. The caps on the lists should all be 105*C rated.
     
  3. Bill S

    Bill S Thread Killer Subscriber

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    Thank you Larry. I had previously replaced caps but left Q1 and Q2 original. I will do that as well as resistors near the large, hot 220 ohm. Also the diode near that hot R. Do you have any suggestion for a replacement for the 5w 220 ohm wire bound resistor on that board? I will mount it higher off the board.
     
  4. rcs16

    rcs16 AK Subscriber Subscriber

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  5. Bill S

    Bill S Thread Killer Subscriber

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    Yep, thanks. I think Ive got a suitable replacement lined up. Just wondering if there was a preferred route. Not my first rodeo with Mouser. Choices can prove daunting with their selection. BOM lists typically have caps and trannys - not resistors. I'll have a go at it.
     
  6. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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  7. Bill S

    Bill S Thread Killer Subscriber

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    Thanks again Larry. I can try them and just raise them way off the board and insulate the leads.
     
  8. Bill S

    Bill S Thread Killer Subscriber

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    Think this board got hot?
    PS board.jpg
    The 220w resistor had opened up the solder joint toward the middle of the board. I checked it and it's still showing 215 ohms of resistance. I'll be changing the other resistors, the 2 diodes and transistors.I'm also looking for more suitable heat sink material. Caps were replaced about 6 years ago and are 105C rated. This should resolve things.
    --Bill
     
  9. Bill S

    Bill S Thread Killer Subscriber

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    Seems to be repaired - playing for a couple hours now. Resistors, diodes and transistors were replaced and resistors raised off the board. Thanks for the help!
    --Bill
     

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