SX-3700 powers on, audio through tape, no speaker output

Discussion in 'Pioneer Audio' started by Gavin Riggi, Aug 11, 2018 at 3:56 PM.

  1. Gavin Riggi

    Gavin Riggi New Member

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    Snagged an SX-3700 and went to put it through its paces, but got nothing on both A and B speaker outputs.

    There's no relay click. Upon visual inspection, no caps are bulging (with the exception of the two large 50v8200uF ones, but I believe that is slight warping of the plastic lids they have). Fuses are not blown.
    I worked all of the switches and pots quite a bit in the hopes a dirty one was the culprit, but no dice. I'm now hoping for some of the infinite wisdom from you find folks.

    Oh, and levels show, but only when the B speaker switch is off.
     

     

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  2. Bob

    Bob AK Subscriber Subscriber

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    do a complete screening. try all switches in the sound path - eg could be a crapped up monitor
    switch.

    try headphones.

    try tape out to another amp - this will verify sound chain to this point,

    try cassette/ipad/CD input to tape in, then tape monitor, verifies the
    front-end working and potentially the amp working.

    post here.
     
  3. Gavin Riggi

    Gavin Riggi New Member

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    Headphone output does not work, tape monitor and in is functioning.
     
  4. Bob

    Bob AK Subscriber Subscriber

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    could you detail how tape in is functioning - this mean there's sound somewhere?
    a and/or b and/or headphones now work?

    tape monitor should be the very last input before line-stage and subsequent power stage
     
  5. Gavin Riggi

    Gavin Riggi New Member

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    A, B, and headphones do not work. Only the tape out has audio. Tape in is functional.
     
  6. Bob

    Bob AK Subscriber Subscriber

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    again, in detail, what does "tape in is functional?" mean?

    the button works?
    there's sound?
    meters show 'audio incoming from tape in' "AND" tape monitor switch is engaged?
     

     

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  7. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    First a good visual check of the insides. The next troubleshooting tactic is check all the power supply feed voltages.
    Also: Check the power supply for any loose components. The set is known for the TO-220 regulators to unsolder themselves.
    Some of the your observations don't seem too add up. Maybe I'm wrong. Or somebody has been tinkering around in there.
     
    Last edited: Aug 13, 2018 at 4:01 PM
  8. Gavin Riggi

    Gavin Riggi New Member

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    Again, there is only audio via the tape out. The tape input is functional, as in when I have a device connected to tape in and enable monitoring, that audio is heard via tape out (I must be out of the loop on what else functional would mean for an input).


    Yeah I figured I'd probably end up needing to get in there with a multimeter and service manual in hand, was hoping there was something quick and dirty I might've overlooked. I'll take a look at the power board for any cracked solder as well.

    Compared to the image in the service manual, the only thing potentially out of the ordinary is a change in cap configuration on the power board, but I'd imagine that was a design change or it's the SX-820 (same manual) as the one on the left has a pioneer ceramic disc cap instead of the standard one, but the space from the right one is empty (beneath the black and yellow wires to the large cap's 1 o'clock).

    Edit: I connected an amp via the headphone jack, and when cranked I can hear the Pioneer's audio, albeit very quiet and heavily distorted with some serious hum, but only when either: a) the speakers I have connected are deselected or b) when no speakers are connected regardless of speaker selection (the hum goes away too). If I have only one channel connected and that set selected, I lose that channel on the headphone out. This happens with both A and B. Hum is there regardless of volume.
    [​IMG]
    [​IMG]
     
    Last edited: Aug 13, 2018 at 7:59 PM
  9. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    This receiver is not for the fainthearted and/or an inexperienced audio tech. But doing some basic voltage checks may give some clues.
    Messing with the receiver anymore will endanger a successful conclusion.
    You know what a DBT is? If not build one and bone up on the schematic.
     
  10. Gavin Riggi

    Gavin Riggi New Member

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    I'm fairly good with circuits and am familiar with DBTs but have not yet built one for myself as I don't have a lot of turnover of receivers with unknown condition. Since I currently don't have a multimeter either, I think I'll take it to a guy I know that's been doing stereo repair for 40 years for aa$30 eval in the interest of saving time. I appreciate your guidance.
     
  11. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    The SX-3xxx series use Pioneers NSA circuit design, which uses high frequency transistors for the amps driver stages. Where most silicon components can be found in equivalent modern packages the ones used in the NSA are extremely hard to match with new. The best replacements come from donor sets.
    Hopefully the receiver only needs a PS rebuild or something that can be repaired with cheap modern components.
     

     

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  12. Bob

    Bob AK Subscriber Subscriber

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    there's another issue here. normally/usually tape out precedes the tape in. example:
    selected tuner/phono sends signal to tape out for recording, then tape in is the
    monitor signal coming into the receiver from the tape recorder. this allows
    signal monitoring for a three head design, and level monitoring for two headers.

    so your external signal coming in should not appear going out.

    in any case, you've exhausted most non- schematic tracing/diagnosing.

    time to send it out.

    I'd send you a free DMM but you'd have to tell me you can read a schematic,
    be able to trace the signal, pull questionable devices and test them.
     

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