Vintage Synth Repair

hi all.
new to this group, was hoping somebody out there can help me with
a repair .... one note is striking at TOP volume. the tech folks at
kurzweil wont help and i dont have the time to send it in. also if
anybody knows where to get a service manual that would also help.
i can repair most of the stuff i've got including a few old ARPS and
KORGS. all help welcomed.
thanx,
andy