No sound sx 838

Discussion in 'Pioneer Audio' started by Pickup1963, Jun 8, 2018.

  1. mbz

    mbz AK Subscriber Subscriber

    Messages:
    2,030
    Location:
    Melbourne, Victoria
    Happy that you asked questions when in doubt, no dumb questions on AK.
    I can manage an oil change, check the radiator, change a tyre, that's about it.

    Test points
    Q7
    collector- pin 34
    emitter- pin 32
    Base-test at R29/D2 junction

    Q9
    collector- pin 37
    emitter- pin 35
    Base-test at D4 cathode

    Q8
    collector- pin 29
    emitter- pin 31
    Base-test at R30/D3 junction

    Q10
    collector- pin 26
    emitter- pin 28
    Base-test at D5 cathode

    Test the collector-emitter combinations first

    Nice graphic from markthefixer on diode testing.
    Red/Black give mm probe orientation, two expected results
    650mV or thereabouts and OL/Open loop/circuit.
    DiodeTest.JPG
     

     

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  2. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    I only downloaded the parts of the manual that I thought I would need.....so I finished the download turns out it has the location of all components
     
  3. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    I just got your other post I'm going to get right on that I have those posted in an hour or so
     
  4. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,763
    Location:
    Glen Burnie Md.
    Pickup; When listing voltages it's easier for us, if you list them in a Vertical format, 1.) list the board number you are testing, and denote if the voltage is A.) + or -, B.) ACV or DCV. Someone down the line may use this thread a a basis for repairing his/her SX-838 with the same problem.

    For example your voltage listing on post #8 should look like this.

    Protection Circuit Assy
    (AWM-025C)

    Pin 1: -39.6DCV............(BAD)(Left Channel In)
    Pin 2: -12.9DCV
    Pin 3: -.303mVDC.........(High but adjustable with bias adjustment on amp)
    Pin 4: gnd.
    Pin 5: -39DCV................(BAD) (Left Channel AMP )
    Pin 6: -39DCV................(BAD) Left Channel AMP )
    Pin 7: -275mVDCV........(Should come down when pin 3 is brought in line with bias adjust)
    Pin 8: -.309mVDC.........(same as Pin 7)
    Pin 9: +35.2DCV
    Pin 10: +34.9DCV
    Pin 11: +34.9DCV
    Pin 12: 7.3ACV

    It identifies the individual board by number and name,(which in some cases can be different in the same model, so it needs to be identified), the individual pin's, and voltages with regard to polarity and whether AC or DC. My notes on the right in paraenthesis are based on expected voltages vs. actual. (See pin 3, 7, & 8 for expected voltages. These are the right channel voltages which look a bit high, but probably can be brought down without too much trouble with BIAS Adjustment on the Right Channel)

    Note that millivolt is written mV as MV would be MEGAVOLT (1,000,000).

    You've probably got shorted output's and possibly drivers on the LEFT CHANNEL.
     
  5. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    OK.....I was wondering how it should be listed
     
  6. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    Here's the voltages off of AWH-031
     

     

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  7. Pickup1963

    Pickup1963 New Member

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    Can't get the format right ....get all voltages in columns and when I post it all changes
     
  8. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    I just wanted to let y'all know that I haven't given up....I got life going on right now thanks
     
  9. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    don't give up on me I'm not giving up on the receiver I just got life happening right now
     
  10. darkhosis

    darkhosis Active Member

    Messages:
    466
    Location:
    Seattle, WA
    While you're waiting for their assistance (I think we all have lives that interfere with the AK stuff sometimes) check out this video of a SX-838 repair. Really helps familiarize you with the machine

     
  11. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,763
    Location:
    Glen Burnie Md.
    When you are listing voltages in columns use periods as place markers.........due to the formatting on the forum will only allow 2 spaces at a time. So periods will keep it all lined up. Gin it up in Notepad or Wordpad with th periods to line up columns, then copy and paste here.
     

     

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  12. Pickup1963

    Pickup1963 New Member

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    PIN 1: +42 vdc. PIN 2: -42 vdc. PIN 3: -5mv. PIN 4: -13 mv PIN 5: -58 mv. PIN 6: -71 mv. PIN 7: . PIN 8: ..... . . PIN 9: -41 vdc. ........ .. PIN 10: -4vdc. PIN 11: 0.00. PIN 12:-13 vdc. PIN 13: grnd. PIN 14: +35Avdc. PIN 15: -24vdc. . PIN 16: grnd PIN 17: -41 vdc. PIN 18: PIN 19:grnd. PIN 20: -40vdc. PIN 21: -39 vdc. PIN 22: -38 vdc. PIN 23: -39 vdc. PIN 24: -42 vdc. PIN 25: +42 vdc AWH-031-A
     
  13. Pickup1963

    Pickup1963 New Member

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  14. LesE

    LesE 110284 Subscriber

    Messages:
    804
    Location:
    Ontario, Canada
    Post assist:


    AWH-031-A

    PIN 1: +42 vdc.
    PIN 2: -42 vdc.
    PIN 3: -5mv.
    PIN 4: -13 mv
    PIN 5: -58 mv.
    PIN 6: -71 mv.
    PIN 7: . PIN 8: ..... . .
    PIN 9: -41 vdc. ........ ..
    PIN 10: -4vdc.
    PIN 11: 0.00.
    PIN 12:-13 vdc.
    PIN 13: grnd.
    PIN 14: +35Avdc.
    PIN 15: -24vdc. .
    PIN 16: grnd
    PIN 17: -41 vdc.
    PIN 18:
    PIN 19:grnd.
    PIN 20: -40vdc.
    PIN 21: -39 vdc.
    PIN 22: -38 vdc.
    PIN 23: -39 vdc.
    PIN 24: -42 vdc.
    PIN 25: +42 vdc


    Right channel appears to be blown. Q6, a 2sc1451, may have gone open as they are know to do which could cause the bias to go to max resulting in widespread damage.
     
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  15. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    Could the microphone have caused the damage. I was given the unit a while back and was told it had lights but no sound so I put it in the attic, got it out couple days ago plugged it in.....it had a little sound and no lights so I changed a fuse and have lights plugged a mic in spoke a few words then pulled the mic and sound quit completely
     
  16. darkhosis

    darkhosis Active Member

    Messages:
    466
    Location:
    Seattle, WA
    I had a 70's drum machine that passed very weak, distorted signal when I first tried it. The second time it got a lot louder after it had been on for 15 minutes, and then went back to being quiet and distorted the next day. It's a sign of failing components that haven't completely died. I recapped the drum machine and it made a total difference - works great now. You'll hopefully see the same result when you restore the 838
     
    Last edited: Jun 14, 2018

     

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  17. mbz

    mbz AK Subscriber Subscriber

    Messages:
    2,030
    Location:
    Melbourne, Victoria
    Either Q12 has failed open or Q14 failed near short.
    Other transistors are likely culprit eg, Q8,10,8,,,
    These should be checked, measure Vdc at
    Q8b/R30
    Q8e/R32
    Q10e/R34
    Q10b/D5
    Q6e/R48
    Q6b/R20
     
  18. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,355
    Location:
    uk.. the middle bit
    yes that is possible .. maybe other faults too for it to happen . really need to narrow things down to one channel or both .
     
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  19. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    Thanks I'll check those out. How complicated is restoration? I guess if i don't try I'll never learn
     
  20. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    ( AWH-031-A) Q8b/R30: -39.5 vdc. Q8E/R32: -40.7 vdc. Q10E/R34: -40.7 vdc. Q10B/D5: -41.6 vdc. Q6E/R48: -42.0 vdc. Q6B/R20: -42.1 vdc
     

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