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Aiwa CX-NAV66 relay clicks then goes dead or stuck on time (standby)

Discussion in 'Electronic Repair' started by HandyMan, Sep 20, 2005.

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  1. HandyMan

    HandyMan Guest

    Hello all,

    I've got a tricky Aiwa CX-NAV66EZ I'm trying to repair. It has some odd
    problems:

    When plugged in, the unit may power up briefly during which time the
    relay clicks a bit madly then it goes dead (display goes off).

    Other times, you can plug it in and it stays on, doing it's silly
    "demo" thing, but when you press the power button or one of the
    function buttons (CD, tape, tuner, etc.) the display reverts back to a
    simple clock and won't come out of it again, no matter what buttons are
    pressed.

    It has also been known to go on and off perfectly, but after about 15
    seconds from plug in, whether you switch it on and off on the front
    panel or leave it alone, the display suddenly dies and leaving it
    unplugged for a minute or two is the only thing which will make it come
    back to life when plugged back in again. It's not doing this at all
    anymore though.

    Also, whenever the bugger did come on properly before dying, the volume
    control was not working properly. It would barely alter the volume
    digits or they'd flick back and forth. Don't know if this is linked.

    Any ideas before it gets thrown over next door?

    Thanks.
     
  2. Arfa Daily

    Arfa Daily Guest

    There are many, many variations of board used in the Aiwas, some of which
    have a discrete output stage using small transistors, some using large
    transistors, and some using various different flavours of STK hybrid. You
    can't even guarantee getting the same board twice in the same model ...

    The problems you describe are usually due to the protection circuit being
    triggered. It pulls a line on the system control micro, and causes a
    complete shutdown. Unfortunately, it's not that simple to track down the
    problem that's causing it, as the protect circuitry monitors supply rails,
    heatsink temp, output stage current and output DC offset.

    If you look around the main board, you'll find a wire link marked " /HOLD ".
    This is the output from the protect sense circuitry to the micro. If you
    measure it, you'll almost certainly find that it's low ie active.
    Unsoldering one end of the link from the board, will usually allow it to
    come back up as a result of a pullup resistor at the micro, on the front
    panel. This will then allow the unit to power, and allow you to figure out
    what's causing the protect circuit to fire. Typical cause is short circuit
    transistors in the outputs. This will almost always blow the 10A picofuses
    on the transformer board ( also some located on the main board in some
    versions ). The centre ( collector ) legs have an oval hole in the pcb,
    which allows for them to be unsoldered from the board to easily isolate the
    centre legs.

    If you manage to get this far and need some further help, mail me direct. I
    have hundreds of Aiwa manuals, and may well have this one, but note that the
    correct model number is the one shown on the back of the unit, not the
    system number on the front.

    The volume control problem is very common on all Aiwa models, and is
    unrelated to the other problem. It's due to the special grease which is put
    into the encoder shaft bearing to give it that
    ' stirring treacle ' feel. It migrates down onto the contacts, and then
    dries out. The encoder can be dismantled once it has been removed from the
    board, and the contacts and encoder wheel carefully cleaned with alcohol.
    The alcohol will make the grease go solid so that it can be picked out from
    the contacts with tweezers. Finish off with a small amount of switch cleaner
    before reassembly.

    Good luck, and hope the above helps ...

    Arfa
     
    Naufal likes this.
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