Pioneer SX-650 Help

Discussion in 'Pioneer Audio' started by Erik67, Apr 29, 2018.

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  1. Erik67

    Erik67 New Member

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    33
    Hey everyone, I have a Pionner SX-650 and I would like some help with it. It works good except it does not work on Phono or Aux. I have a service manual for it but I still need some help. I’ve worked on this receiver a little. I recapped the power supply board but that’s it. I bought this receiver used and it came with the Phono and Aux broken already. Also when using the tape function only one speaker works on stereo but on mono both speakers work. Any help would be appreciated since I’m a beginner at this.
     

     

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  2. Watthour

    Watthour Electron Rancher - JS3600

    Does FM work in stereo mode?

    If so, that eliminates everything from the tone amps onward. Doing that leaves nothing but the function/signal switches. In phono mode there are preamplifiers for each channel, but in TAPE and AUX modes there are only the switches.

    It would be good to verify that the switches have been thoroughly cleaned and de-oxidized, and then lubricated.
     
  3. Erik67

    Erik67 New Member

    Messages:
    33
    Yes Stereo does work in FM. I’ll clean the pots and get back to you.
     
  4. Watthour

    Watthour Electron Rancher - JS3600

    I'd be more concerned with the function switches, but you might as well get them all in good condition.
     
  5. Erik67

    Erik67 New Member

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    Ok I cleaned them all very well with deoxit. The Stereo now works well. I still have no Phono and Aux though.
     
  6. Watthour

    Watthour Electron Rancher - JS3600

    The AUX input is switched by contacts within the MIC jack. If you apply some cleaner to the leaf contacts on the jack and alternately plug and unplug a ¼" phone plug into the jack it should exercise the contacts and hopefully wipe them clean. In that way, when the phone plug is removed from the jack the AUX inputs should be connected to the rotary function switch. As long as all decks of that switch are clean, signal should get through.

    The PHONO input also routes through the rotary selector switch, but after a pair of OP amps used to amplify the signal to a usable level. It's possible the amps could be an issue, or the rotary switch.
     

     

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  7. Erik67

    Erik67 New Member

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    I excerized the contacts as you suggested and still nothing. If I plug in a pair of headphones and turn it up all the way though you can just barely hear it.
     
  8. Watthour

    Watthour Electron Rancher - JS3600

    The signal will have to be traced from the rear panel jacks to the input of the Tone Amp section. This can be done with the unit powered off by using an ohmmeter. Connect one meter lead to the center pin of the AUX input jack and the other to the TAPE 2 Playback jack center terminal. Turn on the TAPE MON 2 switch. Resistance should be 0Ω if the rotary switch and all connections are intact. Do this for both the L and R channels.
     
  9. Erik67

    Erik67 New Member

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    Ok will do when I get home thanks.
     
  10. Erik67

    Erik67 New Member

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    Ok I did it and it was 0 ohms for both channels.
     
  11. Erik67

    Erik67 New Member

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    I was wondering if it turns out to be the transistors in the equalizer amplifier assembly for the Phono. What could I use in place of these transistors. It says to use 2SA725-G and 2SC1313-G and 2SA726-G. Thanks
     

     

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  12. UncleBingo

    UncleBingo AK Subscriber Subscriber

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    The 725/726 are known bad offenders around here. If you can replace them do so. Look for an SX 650 recap list on this site (use Google search Audiokarma sx 650 recap)
     
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  13. Watthour

    Watthour Electron Rancher - JS3600

    That might solve the Phono problem, but doesn't explain the AUX problem.
     
  14. Erik67

    Erik67 New Member

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    33
    Ok thanks, any suggestions on what to do about the aux? Should I try cleaning the function switch again and mic?
     
  15. Watthour

    Watthour Electron Rancher - JS3600

    Since you could read 0Ω from the AUX jacks to the Playback jacks for Tape 2, that should eliminate the MIC jack and all the switch contacts - As long as the meter indication is actually 0Ω on the lowest resistance scale.

    All audio signals from every function are fed to that point by the selection of switches. Beyond that point, there is nothing but the Stereo/Mono switch and balance/volume controls. Those are presumably working since the tuner seems to be operational.
     
  16. Erik67

    Erik67 New Member

    Messages:
    33
    Yeah the tuner works great and so does the tape jacks. If I turn up the Phono all the way there is some sound just very scratchy and distorted, so I will replace the transistors and see if that fixes it. That doesn’t explain the aux though. I replaced the caps in the tuner and Phono section while I was troubleshooting the Phono and Aux as well. Thanks for the help so far.
     

     

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  17. Erik67

    Erik67 New Member

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    So I went to order the transistors and KSC1845EBU is no longer available. What can I use instead?
     
  18. Awesomeaudio

    Awesomeaudio AK Subscriber Subscriber

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  19. Erik67

    Erik67 New Member

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    Thanks
     
  20. slow_jazz

    slow_jazz Lunatic Member

    Messages:
    13,673
    Location:
    SE Michigan, Downriver....
    You could use an external RCA switch box to get more inputs.

    That's what I use with my SX-450.

    Hook up the switch box to the tape monitor that is working.

    Cheap fix.
     

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