From the JCM DBV-200 Bill Validator Operation and Maintenance Manual (Rev B) (I acquired the manual from this from this site)
Referring to the dip switches on board the head.
"With the power off, set the DIP switches for the
test. Set Bank-2 #6 on. Turn on the power. Turn
Bank-2 #6 off. The motor will cycle. Insert a bill."
Once this is done the BV is supposed to accept a bill and then spit it out again.
I could not contact the owner who was selling the machine thru an antique dealer.
There was a note on the machine stating the BV needed an upgrade, but I had no idea what that meant.
This problem has existed since purchasing the machine so no I never have seen it work.
All associated cables have been checked for broken wires or bent pins, nothing abnormal was found.
All I can think of is to try another head