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Vibration failure of components in bass combos

Discussion in 'Electronic Repair' started by N Cook, Jun 11, 2007.

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  1. N Cook

    N Cook Guest

    Yet another one, an unsupported 3W resistor , with a fractured wire.
    Doesn't matter what maker, none of them seem to take this failure mode into
    consideration. The common factors bass combo (so far only bass ones ), large
    Rs suspended off the board, can be mounted vertically or horizontally, the
    fracture always at the pcb and looking at the cross-section of the wire and
    a copper colour then presumably work-hardening via vibration of wires with a
    high copper content.
    I'd never seen Rs supported on ceramic bead insulators with this failure so
    used them on replacements. Then i thought a rigid pillar could exaserbate
    the problem by a fulcrum effect plus chance of them vibrating / rattling in
    use. So later I used beads or PTFE vias for tin-plate (discarding the pins )
    for most of the stand-off and finishing with a blob of RTV silicone.
    This one I'll try blocks of that orange silicone rubber cut from the
    pressure roller at the output of a junked photocopier. Small hole "drilled"
    through each so making fuzzy contact with the R wire and theoretically damp
    any tendency to vibrate. Incidently anyone know what the incredibly firm
    adhesion system they use for bonding that rubber to the steel shaft running
    through the rubber.
    Has anyone seen the pro solution to this problem by any maker or any other
    ideas?

    With a number of such large Rs in a line then I tie each to adjascent with
    stout silicone sleeving with slight tension in the sleeving and anchor to
    the pcb at the ends.
     
  2. Ron(UK)

    Ron(UK) Guest

    Makers like Peavey use hot melt glue or something that looks like very
    thick PVA woodglue.

    Ron(UK)
     
  3. Meat Plow

    Meat Plow Guest

    They've been using that in their lead guitar amps also since the 70's. I
    have 3 of them. I think whatever it is has a much higher melting point
    than hot glue.


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  4. N Cook

    N Cook Guest

    Glooped over the body of the R and the leads or just the leads, cross-linked
    to something else or just glooped onto the pcb ?
     
  5. Ron(UK)

    Ron(UK) Guest

    All the examples I`ve seen have had the stuff poured over the component
    body to an adjacent component or to the pcb, never on the leadouts. They
    seem to use something akin to Evostick around the bases of verticle
    smoothing caps.

    The hard white stuff - more like pva glue than hot melt - tends to
    discolour and crack off the component in time, probly due to heat.

    I doubt using standoffs improves the reliability much unless maybe it's
    the old fender method of using a brass tube fixed through the pcb with
    the leadout wire soldered at the lower end but free to move in the tube.

    Crossover networks often have big components secured using cable ties
    around the part and through the board.

    Big components fall off circuit boards, it`s a law of nature (and bread
    and butter work for repair technicians ;^)


    Ron(UK)
     
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