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NAD 7020e has its signals crossed

Discussion in 'Electronic Repair' started by Nigel Burnett, Aug 28, 2004.

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  1. 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 in advance for help

    Nigel
     
  2. Tim Schwartz

    Tim Schwartz Guest

    Nigel,

    The switching in this receiver is purely mechanical, and all before the
    the volume control, so what you are getting is really odd. I would have
    to guess at a cracked circuit board, or some blown ground foils, unless
    the switch latching mechanism has failed and allowing multiple sources
    to be selected, or there is major corrosion in this unit creating
    unwanted signal paths.

    Regards,
    Tim Schwartz
    Bristol Electronics
     
  3. rosecranz

    rosecranz Guest


    If you want to end that kind of noise, you should add a grounding plug
    to unused inputs.

    When I had the audiovirus back in an earlier lifetime, I used to use
    old RCA plugs cut off a cable, strip the wires and twist them
    together. I actually soldered them. I forget if some people used
    some special value resistor soldered onto the wires instead of just
    twisting them.

    I'm not sure what the deal is with your tuner, I'd think the tuner
    circuits would be turned off if it isn't selected.

    Damn noisy otherwise ;)
     
  4. Hi Tim,

    It is odd. I've ohmed out the signal paths and switches and everything seems ok. Disassembling the switches looks like a
    mechanical nightmare given that 5 ganged xwitches need 6 contacts each desoldered. Phew. It does appear that the Tape
    Monitor is the problem as any signal (even built in tuner) comes through at 1/2 vol. A signal applied to either left or
    right CD input can be heard on both channels when tape monitor is pressed.

    The unit hasn't moved for a year so cracked traces seem almost impossible. No corrosion or anything visible. It could be
    internal to one of the switches I guess. I'm really stumped esp with no schematic. *sigh*,
     
  5. Tim Schwartz

    Tim Schwartz Guest

    Nigel,

    What happens if nothing is connected to the tape in/out jacks? After
    that, try one pair of RCA cables looping from the tape out to the tape
    in, but no equipment hooked up to the receiver.

    Regards,
    Tim Schwartz
    Bristol Electronics
     
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