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Pioneer QX-949 Quad amp....

Discussion in 'Electronic Repair' started by Deke, Jun 20, 2004.

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  1. Deke

    Deke Guest

    This monster was recently given to me by a woman getting rid of her late
    husbands "junk". It hasn't been used for years, but it fires up, all the
    lights work, and the quad display works. All the controls are dirty,
    but they work. Problem is, the right front channel is weak until its been
    on about 5 minutes, then it pops on and off. I suspect bad solder joints, a
    gentle tap on the top will bring the right channel back up for a bit. Rear
    channels are functional also.
    Before I put it on the bench and get started on the basics, anyone have any
    experience with these units? The last one I saw (while drooling heavily),
    was in the Navy exchange on Guam back in 72 or 73.
    Want to get it fully functional, and replace a Proton 930 in the computer
    room
    with the Pioneer. Any info on known faults or weaknesses would be
    appreciated.
    TIA

    Deke
     
  2. Ricky Eck

    Ricky Eck Guest

    Ahhh, finally something from my time and days. I will say at first, that I
    have not worked on this model, but am extremely experienced with this era of
    electronics. It seems you have a simple problem, since you can tap it and
    it will work. I would say, also, it is a bad solder joint. Most of the
    time on the older units, the ones with all the wires, they eventually work
    them self's free from the years of being run. Meaning that the heat from
    them running, and then cooling off, will eventually break them free from the
    PC board. But first thing I would do is clean all the pots and switches.
    Get yourself some tuner cleaner (preferably one with a lubrication agent in
    it, you can usually find this at your local Radio Shack, or part store.) It
    will clean them out, and if this isn't the problem, then at least you know
    that they are clean when you do solve the problem. Sorry I can't be more
    help, but with out it sitting in front of me, I can't see the actual unit.
    Maybe someone else can look at the same pix I looked at and give a more to
    the point answer http://www.classic-audio.com/pioneer/pics/i_qx949.jpg What
    I would do personally, and remember, I am experienced at working on the
    older units. But I would take the top off, and turn it on. Take a Dowel
    rod, or something similar, that is non conductive, and LIGHTLY touch the
    wires, and the individual PC boards, till you find the one giving you the
    problem (Reason I say lightly is because if you tap too hard, it could
    vibrate to the board or wire that is in fault). Then inspect them for lose
    or broken connections. Now, like I said, it is hard to say exactly what it
    could be, with out actually having the unit in front of me, but this is the
    way I would go to trouble shoot the problem. HOWEVER, being that I don't
    know your experience in electronics, I do urge you to use caution. And if
    your experience in electronics is little to none, I urge you to take this
    unit to a qualified tech, dispose of it in the proper manner, or just put up
    with the problem till the unit expires.

    That's my story, and I'm sticking to it,
    hope that's helps.
    Rick
     
  3. That's a nice solidly built machine.

    Good shielding on the tuner, transformer and amplifier.

    Solid looking counterwieght for smooth tuning on the radio dial.
     
  4. Deke

    Deke Guest

    Thanks for the input Rick, I've been working in the electronics field, both
    private and military, since the late 60's.
    I'm really anxious to get into this amp, partially out of curiosity, and
    because I want to revive the old beast. And I have several cans of Channel
    Master "Shield" left (now illegal, but the ultimate cleaner/lubricant), so
    the controls wont be a problem. I've ordered the service manual.
    Just wanted any input from anyone else that may have worked on one of these.
    Thanks again.

    Deke
     
  5. I'd be willing to bet even odds the problem is either dirty switches (probably
    the tape monitor) or else the speaker protection relay contacts. Very common on
    these units.
     
  6. The speaker relay contacts may need cleaning. This model uses those little
    blue Sanyo coupling caps in the tone/pre and main amp input areas; they had
    lots of problems with those.

    Mark Z.
     
  7. Deke

    Deke Guest

    Alan and Mark Z.....Thanks for the input. I'm forcing myself not to even
    crack the case until I get the service manual, plus there's a reel to reel
    spread out on the bench right now, and its a small bench.
    Judging by its weight, 52 pounds, I think my first project will be to a make
    a wooden jig to hold it at a good angle to get to the bottom of the main
    circuit board.
    I noticed the right channel sound cuts off using headphones, so its probably
    in the pre-out section. Have to wait to get the schematics to see what the
    commonalties are.
    Thanks again! Now to get the Sansui SD-7000
    out of test mode, put back together, and off the bench.

    Deke
     
  8. The headphones are run off of the main amp - as they are in most amps. Just
    limiting resistors added. Doesn't eleiminate main amp or relay problems.

    Try tapping on the relay, when you get the chance, and see if that affects
    your problem.

    Mark Z.
     
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