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Pioneer SX-838 voltage problems???

Discussion in 'Pioneer Audio' started by Tomcow, Oct 6, 2018.

  1. Tomcow

    Tomcow Member

    Messages:
    60
    Ok.thanks for the post.One other quick question.the little diode inbetween the 470uf caps,what should that correctly read?
     

     

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  2. Tomcow

    Tomcow Member

    Messages:
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    I will post back later when I have completed the repairs.The electronics world is blessed to have you around!!Best Regards,Thomas
     
  3. Watthour

    Watthour Electron Rancher - JS3600

    Almost all (not all, but almost all) silicon diodes should present the same kind of readings. Zener diodes and tunnel diodes are different components than regular rectifier diodes, and will exhibit different readings, but that's not the case in this instance.
     
  4. Tomcow

    Tomcow Member

    Messages:
    60
    When the new one comes from mouser.Will it need to be mounted a certain way?(facing in or outward)Thanks
     
  5. avionic

    avionic " Black Knights " Subscriber

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  6. Tomcow

    Tomcow Member

    Messages:
    60
    Any input on modern replacements for the 2SC-1451’s in the Pioneer SX-838?About time they were upgraded!Thanks!
     

     

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  7. Watthour

    Watthour Electron Rancher - JS3600

    KSC2690AY or KSC3503 could be used. If you are replacing to improve reliability, consider replacing all the 2SA725 and 2SA726 devices as well. BC550C or KSA992F can be used. 2SC1312 devices can also be replaced with 2SC2240 or KSC1845. Do some more research, since there are several potential problem devices present.
     
  8. Tomcow

    Tomcow Member

    Messages:
    60
    Still in protection mode.Pin 13 on the power supply board supposed to be reading 35V and I am only getting around 14V.Also getting way too high voltage at pin 1 on protection board.The emitters on the output transistors are also reading in high voltage,when they should be well under 100mv.I got to track down the problem at its source,somehow.
     
  9. Tomcow

    Tomcow Member

    Messages:
    60
    Had A bad transistor on the power supply board. Relay clicks on now,only problem now is the regulator transistors,1 reads 47.5 V coming in,35V out on the emitter,the other one reads 25V coming in and only 13V going out.No sound yet at speaker terminals.Getting 40-45mv at the emitters on the output transistors on the right channel,300-320mv on the emitters on the left channel.Not quite there yet
     
  10. avionic

    avionic " Black Knights " Subscriber

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    Thats what it should be.. Q2 47v on the collector and 35 on the emitter. Q1 25v on the collector and 13v on the emitter.
     
  11. avionic

    avionic " Black Knights " Subscriber

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    Are the pre-out/ main-in jumpers in place?
     

     

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  12. avionic

    avionic " Black Knights " Subscriber

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    How are you measuring these. What are your meter lead connections?
     
  13. Tomcow

    Tomcow Member

    Messages:
    60
    With the black probe on ground,I measure the 4 emitters-on the output transistors,27 and 30 on the right channel,pins 33 and 36 on the left channel.jumpers are in place.Cant figure why there is no sound and why dc is so high on the left channel.Right channel adjusts to 0 dc and 30 my bias,still no sound.Will continue to evaluate.
     
  14. Tomcow

    Tomcow Member

    Messages:
    60
     
  15. avionic

    avionic " Black Knights " Subscriber

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    42,858
    Location:
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    Are both jumpers in place?
     
  16. avionic

    avionic " Black Knights " Subscriber

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    Have you got a separate amplifier or pre-amp? A quick way to determine if you have an amp or preamp problem.
     

     

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  17. petehall347

    petehall347 the brandy coffee man Subscriber

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    wet finger on each jumper should make a nice speaker buzz .
     
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  18. Tomcow

    Tomcow Member

    Messages:
    60
    Yes I do have 3 other receivers.I will try that(they all have pre-out main in jacks)
     
  19. Tomcow

    Tomcow Member

    Messages:
    60
    Really?????
     
  20. petehall347

    petehall347 the brandy coffee man Subscriber

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    yes . no harm if done quickly .
     

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