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SX-650 Very Low Output on One Channel - All sources except tuner

Discussion in 'Pioneer Audio' started by spark1, Oct 23, 2018.

  1. spark1

    spark1 Super Member

    Messages:
    1,480
    Location:
    The Great Midwest
    My daughter bought an SX-650. She was clever enough to test it out before buying, but had only its tuner as a source. Seemed to work just fine.

    She brought it home for me to clean up and refinish the cabinet. I thought I would go ahead and check it out more thoroughly, so connected an iPod (known to be working with no problems) to the AUX. Right channel output is very low. Plugged it into TAPE 1 and TAPE 2...same result. Swapping input cables R to L and L to R makes no difference.

    I'm assuming that the fact that tuner output is good on both channels tells me the outputs (STKs) are good? If so, I sure would appreciate any suggestions on how to diagnose/isolate the problem.

    I can test components, measure voltages, do decent soldering work and follow directions, but I'm very weak with reading/interpreting schematics.

    All pots and switches have been cleaned with Deoxit, although given the symptoms my expectations for a Deoxit miracle were quite low (appropriately so, as it turns out!).

    Thank you for any help you can provide.
     

     

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  2. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

    Messages:
    4,851
    Location:
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    When the tuner is selected it plays fine?
    When on other line level inputs the right channel is low?
    More cleaning.
    Sometimes you might need to remove the pots gaining better access for the straw. Volume pot in this case.
    The toggles can be removed and taken apart for better cleaning.
    The power switch on these are known for poor connections causing low or no power. Bypassing the power switch with a jumper may shed some light if both channels are low.
     
    Last edited: Oct 23, 2018
  3. spark1

    spark1 Super Member

    Messages:
    1,480
    Location:
    The Great Midwest
    Output is perfect on both channels with its tuner as input.

    Output of right channel is VERY low when using external input (connected to AUX or TAPE 1 or TAPE 2).

    I very much appreciate your suggestions, but wouldn't a problem with the volume control or the power switch/speaker selector affect tuner input as well as other inputs?

    Unit was fully disassembled (front panel and front chassis plate) for cleaning pots and switches.
     
    Last edited: Oct 24, 2018
  4. Porkbuns

    Porkbuns New Member

    Messages:
    25
    If someone's serviced it before you can always check and see if someone's fiddled with the muting circuit. I doubt that's the case.

    I would say check one of the interconnect boards that go before the tone control. usually with pioneer designs the input switch assembly connects to a PCB (that filters signal). There might be bad connections or leaky caps there since the tuner usually bypasses this and goes straight to the tone controls.

    An oscillioscope would help out a lot. I'm going to think it's those culprits because the tuner is unaffected. Try tracing out the signal path and comparing between tuner and aux/tape monitor.

    Alternatively check your tape monitor pot (from record to source), there have been issues where that pot is dirty and it causes issues.
     
  5. Watthour

    Watthour Electron Rancher - JS3600

    Another vote for cleaning and lube of the mode switches.
     
  6. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

    Messages:
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    Correct, Not sure what my thought was on that statement.
    Still a good cleaning, probably more that others sets might need.
     

     

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  7. spark1

    spark1 Super Member

    Messages:
    1,480
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    I cleaned all pots and switches again, very thoroughly (as I had already done once). No change.

    I could certainly take the selector switch apart for an even deeper cleaning if there is still a chance it is the culprit, but If it is the issue, wouldn't the use of the tape inputs "bypass" the problem? As I mentioned above, the low output is unchanged when using tape inputs and activating the appropriate tape monitor switch.

    Doesn't the problem have to be downstream of the volume, balance and selector pots/switches?
     
  8. 7367ruffles

    7367ruffles New Member

    Messages:
    1
    Since you have cleaned the controls, I can only assume that the problem is downstream from the bass, treble, balance and source knobs. It may be bad solder joints on the non-tuner inputs, but I don't know unless you test further.

    Is the channel imbalance present in the tape/preamp outputs?
     
  9. avionic

    avionic " Black Knights " Subscriber

    Messages:
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    Location:
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    Function switch is still fouled or is " borked" or possibly the wiring to or from the switch. Wafer Switch Sa1..............
     
    Last edited: Oct 25, 2018
  10. spark1

    spark1 Super Member

    Messages:
    1,480
    Location:
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    I would not characterize this as a channel imbalance. It is much more extreme.

    As noted above, the problem occurs on all inputs except tuner.

    What testing do you suggest?
     
  11. spark1

    spark1 Super Member

    Messages:
    1,480
    Location:
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    Thanks. I'll dig deeper into the switch and wiring from/to.

    Do you know at what point the signal path from the tuner and from the other inputs becomes the same? It would seem to me that the problem must lie "ahead" of that point.

    Do you happen to know the relationship between the selector switch and the tape switches? Do the tape switches "bypass" the selector switch upstream or downstream from it? Seems like this might help to narrow down where the problem is?
     
    Last edited: Oct 26, 2018

     

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  12. avionic

    avionic " Black Knights " Subscriber

    Messages:
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    The wiper of the function switch.
     
  13. spark1

    spark1 Super Member

    Messages:
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    Location:
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    Thanks. That's what I would have guessed. Where do the tape switches sit in the path? Downstream from the selector? If so, I understand the emphasis on the selector as the culprit.

    Usually if it is a dirty/oxidized switch you get at least an occasional moment of good signal when miving the switch to and fro, but in this case a big nada.
     
  14. avionic

    avionic " Black Knights " Subscriber

    Messages:
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    Location:
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    The switch itself may be history.
     
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  15. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,806
    Location:
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    Same function switch.
     
    Last edited: Oct 26, 2018
  16. avionic

    avionic " Black Knights " Subscriber

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    Downstream between the switch Sa1 and the AWG-049 Tone board. Are you getting good audio out of the REC OUT/Tape Monitor? Probably not.
     
    Last edited: Oct 26, 2018
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  17. avionic

    avionic " Black Knights " Subscriber

    Messages:
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    Is the function switch a chassis mounted or board mounted switch? Board mounted.
     
    Last edited: Oct 26, 2018
  18. spark1

    spark1 Super Member

    Messages:
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    Location:
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    I haven't checked tape out...just tape in (which has the same low output in right channel). I will try it tomorrow. Sure do appreciate the help.
     
  19. spark1

    spark1 Super Member

    Messages:
    1,480
    Location:
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    Board.
     
  20. Porkbuns

    Porkbuns New Member

    Messages:
    25
    Might be time to bust out the Oscillioscope and trace where the signal gets weaker.

    Now that I think of it, it might be related to a filtering cap or a transistor on the tone control circuit. The SX-x50 series had two separate inputs to the tone controls if i remember. One was from the tuner (which was actuated through the input selector) and the other was from the rear inputs. It might also be worth your while to check of any power supply irregularities.
     

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