what type do you have? flip it over and if there is a eprom in the opening, then a newer eprom will up grade it, if it is flashed memory, then the latest software will have to be downloaded into the unit. in any case, the unit , if working should take more than a dollar. probably the older style bills.
you can determine what it will take, do this stand alone test, using the machine and the power supply normally used to power the head, there are two banks of switches on the bottom, one has 10 switches, the other has 6, all should be in the same direction, with no power on the unit, flip number 6 in the 6 bank switch to the opposite direction, now apply power, flip number 6 in the opposite direction, unit should cycle briefly, now you can insert bills into the unit, doing this you are able to determine what it will accept ( you can do this with the head detached from the transport and hold it in your hand.
I have the ability to upgrade and calibrate the heads provided they are working units. I do not have parts to repair units that do not work!
Jim