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Repost: NAD 7020e has its signals crossed

Discussion in 'Electronic Repair' started by Nigel Burnett, Aug 29, 2004.

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  1. Reposting as this hasn't shown up on rogers nntp. Their news servers are reposting stuff from 2002 however!

    NAD 7020e receiver just failed most strangely. If only one source is connected to the appropriate input (such as CD),
    the signal can be heard on both channels at about 1/2 volume when tape monitor or video is selected. Tuner is also
    audible regardless of which input is selected.

    I've disassembled it and cleaned contacts etc to no avail. There's no visible damage under illuminated magnifier.

    tia for help

    Nigel
     
  2. Jerry G.

    Jerry G. Guest

    If this receiver uses a IC for the input switching control, this IC is most
    likely defective. I have seen this before in other models. It would be easy
    to verify following the service manual, and with a scope and DVM to follow
    up on the supply voltages and the signal paths.

    Your best bet is if you are skilled enough you can try servicing it by
    changing the control IC, or if not, you can give the receiver out to their
    authorized service rep to have it serviced.

    --

    Jerry G.
    ==========================


    Reposting as this hasn't shown up on rogers nntp. Their news servers are
    reposting stuff from 2002 however!

    NAD 7020e receiver just failed most strangely. If only one source is
    connected to the appropriate input (such as CD),
    the signal can be heard on both channels at about 1/2 volume when tape
    monitor or video is selected. Tuner is also
    audible regardless of which input is selected.

    I've disassembled it and cleaned contacts etc to no avail. There's no
    visible damage under illuminated magnifier.

    tia for help

    Nigel
     
  3. JVC dude

    JVC dude Guest

    does sound just like the symptoms you get with an IC based input switcher,
    but someone says its mechanical based yes?
    Is it those circular sets of brown wafers? twisted/ missing contacts can
    give weird symptoms on them. If they are the long rectangular type then they
    are unlikely to fail, you would just get odd missing channels.
    AW

    reposting stuff from 2002 however!
    connected to the appropriate input (such as CD),
    monitor or video is selected. Tuner is also
    visible damage under illuminated magnifier.
     
  4. definetly mechanical - rca jacks to m/b to cable to m/b to switches - long rectangular dpdt push/latch push/unlatch.
    classic 1986 technology. ohming them out says everything is ok. I suspect tape monitor switch but how the other
    signals are sneaking around the back is quite baffling. Signal applied to either channel (say on CD input) can be
    heard on *both* channels at 1/2 volume when tape monitor is pushed. This should be easy - I wish it had just
    blown up; I wouldn't feel obligated to fix it :)

    Nigel
     
  5. jakdedert

    jakdedert Guest

    Is it dirty? There are many possible leakage paths in old equipment. If
    there is dust which has become conductive from humidity--combined with
    possibly not optimum pcb design--it could act like that.

    Perhaps there is an output/intermediate stage which has lower gain than
    normal. Something like that would necessitate cranking the volume to
    compensate, thus exacerbating any normal leakage. Most consumer gear has
    'some' leakage, but it's not noticable at normal gain levels. How far are
    you turning the volume control? Most amps should produce moderate
    real-world levels at well under the 12 oclock position on the volume control
    (In fact on nearly every amp/reciever I've used, halfway up is where
    distortion occurs with most signal sources.). Is there a 'mute' button, and
    is so, is it on?

    jak
     
  6. boomer

    boomer Guest

    Those switches are most likely the problem. Spray them ALL with
    contact cleaner. Works best if there's an open rear on the switch,
    but you can try getting it into whatever holes are available. On the
    really long switches, it can be hard getting the cleaner where it
    needs to go. Sometimes you can release a wire clip at the front of the
    switch and actually pull out the push rod for cleaning. If all else
    fails, i've had luck drilling a small hole for the spray tube in the
    extreme rear of the switch if there's a little room.
     
  7. JVC dude

    JVC dude Guest

    I'm intrigued by this.

    I presume from the details gathered so far that the inputs are self
    cancelling switches ie tuner, cd phono etc cancel one another ~(or should
    do!) and the monitor switch is as you say a dpdt latching type.
    The tell tale symptom must be the fact that a single channel appears on both
    channels. there are very few possibilities for this to occur since each
    channel is quite independant, even in all the switching the channels are
    seperate. The only areas I can think are around the balance control: a
    fractured/damaged balance pot may cause this; or a problem in the tone
    stage if it uses an Ic .(psu problem probably).
    I can't see how this symptom is linked to the other one where the inputs are
    bridged. An incorrectly positioned selector switch may cause the bridging,
    and would even explain the loading down to 1/2 volume but wouldn't be
    permanent, it would change as you pressed the selectors and the switches
    certainly couldn't cause a mono problem.
    Perhaps there are leaky caps with the acid causing tracking? this should be
    clearly visible, yet I assume you would have seen it. Improbable however.
    Broken tracks? not likely. certainly a missing earth would not account for
    both symptoms. Bridged solder somewhere: plausible.

    Sorry I can't pin it down closer yet. could do with a circuit diagram.
    AW
    if you have more info :
    try me direct service at wilkinsons dot tv
     
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