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Ashdown MAG 300 amp, 2004

Discussion in 'Electronic Repair' started by N_Cook, Jul 30, 2013.

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  1. N_Cook

    N_Cook Guest

    Both 6.3amp fuses blown, 2 diodes of the bridge rectifier s/c. Internal
    failure of this bridge, dodgey looking splodge logo, presumably Fronter
    logo and 8amp rating, marked
    AC BP8-04
    or something else to change as well?
    Main caps look ok and ESR (for what its worth in such cases) ok
    The 2 failed diodes are
    -ve to AC
    +ve to other AC
    Suspiciously 2 solder points look like crazed PbF solder but all is SnPb,
    melted and reformed? the 2 points are at the -ve terminal and the AC
    terminal of the other failed diode. Output devices DVM-D cold test as
    expected. No heated traces or even obvious gaseous eruptions from the
    bridge or anything out of the normal. No reported preceeding noises
    prior to failure.
     
  2. N_Cook

    N_Cook Guest

    No , output devices, cold test , seem fine.
    Looking at the Fronter datasheet, the bridge has to be derated to only 3
    amps at 40 deg C, which seems surprisingly low temp. This amp was all
    day sitting outdoors in the cloudless sun and failed after 1 hour of use
    in a set. So 40 deg C was quite likely exceeded, so probably the reason
    for failure.
    As constricted in space , without going off board, I see a heatsink
    being bolted to the replacement same rating bridge, or wiring off board
    and bolting to the chassis
     
  3. N_Cook

    N_Cook Guest

    I cannot see how an honest rated 8amp bridge could be in a 15mm square
    pack. Replacement will be 4 amp 200V rating, with a hole to take a vaned
    heatsink, no hole in the original (perhaps to get 8A it uses the central
    area). The fan airflow in these amps is fine for the output heatsink but
    the bridge is sheltered by the main caps and wiring knot, vane will be
    off-centre poking into clear air, off the edge of the board
     
  4. N_Cook

    N_Cook Guest

    I picked up the wrong bridge, the original Frontier one does have a
    central hole
     
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