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Need help repairing vintage receiver

Discussion in 'Electronic Repair' started by Mark, Jan 8, 2004.

  1. Mark

    Mark Guest

    Hi

    I recently got hold of an old Hitachi SR-703 receiver that's been in
    an attic for 15 years.

    I hooked it up and it appeared to work, the FM signal strength meter
    was high, the stereo beacon was on and it sounded good. Then after
    about 1 minute the stereo beacon went out and I lost the sound. The
    signal strength meter was still high, the FM centre meter was still in
    the centre, just no sound and no stereo beacon. I can tune in all my
    local FM stations with high signal strength but still no sound and no
    stereo beacon.

    AM works fine, phono, and aux inputs work fine, power supplies appear
    OK. The FM muting button is switched off.

    I've checked the entire tuner board for dry joints and found none.
    I've replaced the stereo decoder chip (HA1196), I've replaced the FM
    IF amplifier chip (HA1137). The only other chips on the tuner board
    are an HA1151 which I believe is an AM decoder (so I assume it's OK)
    and an HA1142 which I believe is an input preamplifier (also assumed
    OK).

    I don't have a circuit diagram so I'm lost for ideas. The fact that it
    worked perfectly for 1 minute after 15 years storage suggests
    something like a dried out capacitor, but I would have expected this
    kind of fault to affect other areas of operation.

    Any ideas greatly appreciated, it would be a shame to scrap this well
    built and once well respected piece of kit.

    Thanks
    Mark
     
  2. Aries Quitex

    Aries Quitex Guest

    Fine unit, as far as I know.
    Resolder, anyway. There is a 10% chance that there are dry joints, but you
    just don't see them.
    Maybe there is a crystal resonator that aged under the extreme climatic
    situations on the attic? Sometimes they are in an orange or blue
    plastic-case about the size of a 6-pin DIL, but stand upright on 2 pins.
    Also there are units in small ceramic 3-pin housing.
    Lesson one from first year of R&TV-Tech apprenticeship:
    Always junk the 100µF capacitors against new ones.

    Due to whatever reason they have the highes fault rate of al ElCaps.

    When you have an oscilloscope handy (Lucky one, if) check if there's any
    audiofrequency (AF)-signal coming out of the FM-Board (assuming that a
    1985-model still used separate boards for amp, fm and am)
     
  3. Asimov

    Asimov Guest

    "Mark" bravely wrote to "All" (08 Jan 04 02:48:52)
    --- on the heady topic of "Need help repairing vintage receiver"

    Check the ESR of the electrolytic caps around the stereo decoder IC,
    quadrature coil or detector, and tuner board supply filters, often at
    one edge. The tuning voltage comes from the tuner front end but the
    audio comes from the 10.7MHz quadrature coil (or dectector) ahead of
    the stereo decoder. You should find a mpx signal at the output of the
    dectector using an audio signal tracer, if not then it could be the
    detector itself or its driver. What IC is used for stereo decoder?

    Ma> From: (Mark)

    Ma> Hi

    Ma> I recently got hold of an old Hitachi SR-703 receiver that's been in
    Ma> an attic for 15 years.

    Ma> I hooked it up and it appeared to work, the FM signal strength meter
    Ma> was high, the stereo beacon was on and it sounded good. Then after
    Ma> about 1 minute the stereo beacon went out and I lost the sound. The
    Ma> signal strength meter was still high, the FM centre meter was still in
    Ma> the centre, just no sound and no stereo beacon. I can tune in all my
    Ma> local FM stations with high signal strength but still no sound and no
    Ma> stereo beacon.

    Ma> AM works fine, phono, and aux inputs work fine, power supplies appear
    Ma> OK. The FM muting button is switched off.

    Ma> I've checked the entire tuner board for dry joints and found none.
    Ma> I've replaced the stereo decoder chip (HA1196), I've replaced the FM
    Ma> IF amplifier chip (HA1137). The only other chips on the tuner board
    Ma> are an HA1151 which I believe is an AM decoder (so I assume it's OK)
    Ma> and an HA1142 which I believe is an input preamplifier (also assumed
    Ma> OK).

    Ma> I don't have a circuit diagram so I'm lost for ideas. The fact that it
    Ma> worked perfectly for 1 minute after 15 years storage suggests
    Ma> something like a dried out capacitor, but I would have expected this
    Ma> kind of fault to affect other areas of operation.

    Ma> Any ideas greatly appreciated, it would be a shame to scrap this well
    Ma> built and once well respected piece of kit.

    Ma> Thanks
    Ma> Mark

    .... Which sparks some mnemonic circuitry.
     
  4. Asimov

    Asimov Guest

    "Aries Quitex" bravely wrote to "All" (08 Jan 04 12:16:29)
    --- on the heady topic of "Re: Need help repairing vintage receiver"

    AQ> From: Aries Quitex <>
    AQ> Lesson one from first year of R&TV-Tech apprenticeship:
    AQ> Always junk the 1005F capacitors against new ones.

    AQ> Due to whatever reason they have the highes fault rate of al ElCaps.

    I thought it was 1uF 50wv electros...

    .... KPLA: Klingon radio: All glory, all the time!
     
  5. Jerry G.

    Jerry G. Guest

    The easiest way to fix this, is to get a 100 mHz scope, and trace the signal
    path starting from the tuner section through. You will find where the signal
    is stopping. I suspect an IF, detector, or AGC problem. It may be as
    simple as the signal not passing through the selector switch, or there may
    also be a muting problem.

    --

    Greetings,

    Jerry Greenberg GLG Technologies GLG
    =========================================
    WebPage http://www.zoom-one.com
    Electronics http://www.zoom-one.com/electron.htm
    =========================================


    Hi

    I recently got hold of an old Hitachi SR-703 receiver that's been in
    an attic for 15 years.

    I hooked it up and it appeared to work, the FM signal strength meter
    was high, the stereo beacon was on and it sounded good. Then after
    about 1 minute the stereo beacon went out and I lost the sound. The
    signal strength meter was still high, the FM centre meter was still in
    the centre, just no sound and no stereo beacon. I can tune in all my
    local FM stations with high signal strength but still no sound and no
    stereo beacon.

    AM works fine, phono, and aux inputs work fine, power supplies appear
    OK. The FM muting button is switched off.

    I've checked the entire tuner board for dry joints and found none.
    I've replaced the stereo decoder chip (HA1196), I've replaced the FM
    IF amplifier chip (HA1137). The only other chips on the tuner board
    are an HA1151 which I believe is an AM decoder (so I assume it's OK)
    and an HA1142 which I believe is an input preamplifier (also assumed
    OK).

    I don't have a circuit diagram so I'm lost for ideas. The fact that it
    worked perfectly for 1 minute after 15 years storage suggests
    something like a dried out capacitor, but I would have expected this
    kind of fault to affect other areas of operation.

    Any ideas greatly appreciated, it would be a shame to scrap this well
    built and once well respected piece of kit.

    Thanks
    Mark
     
  6. Sofie

    Sofie Guest

    ...... gee.... I always thought it was the 330uf and 1000uf @ 6.3 V and 10
    V.
     
  7. Mark

    Mark Guest

    Stereo decoder chip is Hitachi HA1196, I replaced it already.
     
  8. Sunny

    Sunny Guest

    My SR-503L (purchased new in 1979) is still *in* the attic because it
    developed the exact same problem shortly before the last time we moved
    house, and I haven't gotten around to looking at it. It's very similar
    to the SR-703 - just has lower output power IIRC.

    Not sure if this could be a hint as to the cause, but for quite some
    time turning the FM mute on for a few seconds, then back off would
    restore sound on mine - this trick no longer worked last time I had it out.

    The owners manual includes a block schematic, but not a full circuit
    diagram. If this would be of any assistance I'd be happy to scan and
    mail to you.

    Needless to say I'd appreciate your posting the fix if found.
     
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