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missing SMD component

Discussion in 'Electronic Repair' started by Cydrome Leader, Nov 26, 2012.

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  1. I had a bench power supply finally act weird, which I only noticed when
    playing with one of the UV LEDs, which even radio shacks sells now.

    At one point, when in CC mode, the LED started to flicker and the power
    supply made a weird clicking sound.

    Outside of CC mode, the output looked OK. The B output (dual output unit)
    worked fine.

    The maker, TTI in the UK kindly supplied the service manual which I wanted
    for the recalibration steps.

    It turns out one of the internal -5v regulators (just a zener) for
    powering the front control panel was completely missing. I had no idea it
    belonged there as the board looked pretty clean with nice solder fillets
    on the 3 pads where the sot-23 zener belonged. Super close inspection
    showed there may have been glue/flux/something where the body of the diode
    was.

    I guess it never wetted correctly at the factory and then 5 years later
    FINALLY fell off.

    So the lesson is two fold

    - check the power supplies inside broken power supplies
    - maybe missing parts weren't options or ECs.

    If anybody in the US has a spare BZX84C5V1 5.1V 350mW sot-23 zener they
    can drop in an envelope, I'll send a few bucks your way. drop munge from
    my email address.
     
  2. One of the three leads had no electrical connection, but had a solder pad,
    with just a nice lump of solder.

    The energy in that section is pretty low, but who knows, maybe it did melt
    and fly away.
     
  3. mike

    mike Guest

    You can get 'em off ebay dirt cheap free shipping.
    I bought some, but they were SOD-323.
    Is the board spacing so close you can't cobble in a leaded part and be done
    with it?
    Insistence on the correct part is overrated ;-)
     
  4. N_Cook

    N_Cook Guest

    It does not take much of a jar to loosen a SMD that was only marginally held
    in the first place.
    As unlikely it will get jarred now on the bench, I would wire in a
    conventional zener , perhaps with a sub-mm drill hole through the pcb, if
    concerned about structural integrity
     
  5. It would actually be more work to take the PCB out of the chassis to do a
    weird retrofit, although there's plenty of space.
     
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