Vintage Synth Repair

my newly acquired sbx-10 has a tempo problem. when i got it, one of
the pads(for the tempo knob) on the pcb was lifted. i desoldered,
scraped away some of the trace and resoldered, plus i soldered a short
piece of wire from the terminal to the next contact down the line,
just to be sure. still nothing. i brought it to a tech who tested it
and said the pot itself was fine. so the problem is somewhere else.
the tap button works, so i know the tempo function is working, but
there's a problem somewhere between it and the knob. any thoughts?
does anyone have a service manual?
thanks,
shayne