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Laney Cub 12R

Discussion in 'Electronic Repair' started by Phil Allison, Aug 12, 2013.

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  1. Phil Allison

    Phil Allison Guest

    ** Ever see one of these ?

    An evil mix of EL84s, ECC83s and SMD on the same PCB.

    Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
    sockets.

    But none of these were the problem.

    The amp would run OK for about 10 mins and then power itself down - all the
    lights go out and the sound fades away.

    Turning the power off and waiting a few minutes restored operation, but not
    for long.

    Who has come across this one?



    ..... Phil
     
  2. tm

    tm Guest

    I have never seen one of those but a first guess, look for a cracked smd
    resistor that opens up with heat.
    Maybe you can spray some freeze spray around to see if you can localize the
    problem.

    Is it RoHS?
     
  3. Phil Allison

    Phil Allison Guest

    "tm"
    ** All the clues are there.

    The amp powers itself off, valve heaters and the dial light goes out and
    will not restart by itself.

    A few minutes with the AC off does the trick.



    .... Phil
     
  4. Phil Allison

    Phil Allison Guest

    "Arfa Daily"
    ** LOL !!
    ** Give that man a Kewpie doll.................

    ** For some whacky reason, the Chinese included a PTC ( aka Polyswitch ) in
    series with the 6.3 volt AC heater supply - adding to their bad judgement,
    they picked one with too low a current rating.

    The heater draw in the Cub 12R is a tad over 3 amps ( = 20 watts) and is
    the largest load on the AC tranny.

    Seems these Polyswitch devices deteriorate with age, if run hot all the
    time - until they trip and go high resistance. With no heater supply, the
    dial lamp goes out and the amp goes slowly silent and the same scenario can
    be repeated indefinitely.

    From reading the Laney user's forum, the fault is endemic with the model and
    you need to fit a 6 amp rated PTC to fix it for sure.

    Or just leave it out.


    .... Phil
     
  5. josephkk

    josephkk Guest

    That sounds like it could easily be a dying polyfuse.

    ?-)
     
  6. Phil Allison

    Phil Allison Guest

    "Arfa Daily"

    ** Errr - he just answered one ...




    .... Phil
     
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