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Yamaha Stagepas 300 loss of one channel

Discussion in 'Electronic Repair' started by N_Cook, Apr 21, 2012.

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  1. N_Cook

    N_Cook Guest

    As peresumably another bloody PbF fault both channels are fine with me and
    failing channel not known. From my reading of the circuit as the owner could
    carry on with
    one channnel (half mono rather than half stereo, as a mono amp) the
    protection circuit must have stayed inactive. So ps and DC of both pa must
    be ok so leaves output wiring from an amp which is pretty robust or mixer
    stage between the dividing path of IC203 , IC206 , speech/music switch and
    the "stereo" master pot or preamp area of an output amp, or is there another
    area that could lead to this situation. When it was consistent failed, the
    owner swapped leads around and confirmed not a speaker or speaker-lead
  2. N_Cook

    N_Cook Guest

    That daughter board with the reverb that slots down into the small fan
    outlet duct is also in line. If absent then it kills the output audio , both
    ch, and protection stays inactive. The 4 opamp section rather than the
    reverb section
    is a line in or out there is broken then loss of a channel, reverb filter is
    monofied I think.
    Nothing hot on that board in use, just
    somewhere to stow it presumably.
    Incidently its headers need a needle inserted to separate as nibs hold the
    header in more firmly than usual headers.
    As this is an early one without the extra vent holes then perhaps overheats
    a PbF joint on this board or headers although no obvious cracks/movement
    seen under x30.
    Looks like one of those suck-it-and-see / cross-fingers jobs, redo main
    solder joints there, sets to header pins and return to owner if engraving
    tool vibration/hot air ellicits nothing. If it recurs then at least get them
    to note which channel
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