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Yamaha Stagepas 300 loss of one channel

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 problem

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N_Cook
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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

Reply to
N_Cook

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