Sansui 661 power issues

Discussion in 'Exclusively Sansui' started by Bert Beukema, May 14, 2018.

  1. Bert Beukema

    Bert Beukema Active Member

    The Netherlands
    Hi Guys,

    So on my repair desk is an old Sansui 661. This one has an odd problem. It will play fine and my systems don't detect any issues. All voltages check out. However, when I open the volume, at a certain point (not very loud) it will crash. Same thing happens when bass or loudness function are triggered (button and potentiometer). On a dim bulb it is very visible; it will initially be very dim as it should be. Pressing the loudness function immediately triggers an overload (which also starts to flip out the speaker relay). Turning the volume knob slowly will increase the brightness of the dim bulb exponentially until the system crashes. Oddly enough, the receiver lamps will also start to pulse brighter and dimmer.

    Obviously the first suspect is the power section, i've rebuilt it with vishay capacitors and film where possible. This did not change the problem. I'd also did the same with the amplifier output stage, also no change to the problem. Transistors were pulled from the power section but checked out fine; replaced them with new specimens as a precaution. No change to the problem.

    I can understand the volume potentiometer causing a power increase in the system and something failing. But the loudness and bass functions are really simple, there is not a lot there that would cause the system to crash. As a precaution I changed the transistors and capacitors on the equalizer board, that didn't change anything.

    Does anyone have a clue as to which element might be suspect in this regard? Perhaps the fact that the lamps are pulsing is a hint?




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