Maker Pro
Maker Pro

BIC D-121OR Powered Sub Auto-on not working



Jan 1, 1970
I am looking at this powered sub because it wouldnt turn on anymore, fuse
was blown. Opened it up, and 2 6800mF 63v caps where blown. Checked the
diodes and bridge they both checked out good. Put 2 new caps, and turned it
on with no audio being feed to it. The green power light comes on when the
switch is set to "on". When you put the switch to "off" a 24v relay goes
nuts, cycling at like 10hz. When you switch it to "standby" somes the relay
goes nuts and sometime it just turns on. When the switch is in "auto" the
amp should go into standby mode when no audio is detected, when in "off" it
just always be in standby mode. I noticed this unit has a 2SD669A / 2SB649A
pair and the resistor to the 2SD669A that feeds the emitter is a little
black. I traced it and it goes through a zener, and hooks the the emitter
of the 2SB649A? My question is how do they interact in a circuit together?
And would this cause the problem that I am having? Should there be
something else I should be looking at?

Thanks for any info