Question about a bill validator

[spidermonkey]

I picked up a Midway Mortal Kombat 4 cab a while back. It has two coin mechs and a bill validator in the upper left hand corner. I think its a "CC" brand door but I'd have to check again to confirm. Anyway, my question is how did these work when you inserted a dollar bill. Did it consume the amount of quarters that was required to start the game and spit out the remaining quarters or did it just give you back your four quarters and then you had to deposit however many quarters to start the game?  If it did recognize the doller bill to start the game then what sent the signal to start the game ? I know how the coin mechs work but do the bill validators work the same way ? Is there some kind of switch inside that gets tripped when the bill goes in causing the game to start ? I'm just trying to figure out if the validator can be utilized with MAME or should I just forget about it and leave it disconnected ? I know there's really no point in having a working bill validator in my own home but then again there's no point in having working coin mechs either but I still love knowing that they work and sometimes use em. . I guess I just figured that since it does have a validator then why not have it functional right ? Any ideas on which way these work ? I was pretty much out of the arcades by the time games came with built in validators so thats why I don't know if they are just change makers or a 2nd means to activate the game.
Thanks for any input.

[paigeoliver]

A bill validator works by sending the PCB a set number of "pulses" per bill (which is configurable). They are usuable in Mame. But many of them require a controller board or box, which is often absent in resold units.

It hooks up similarly to a coin mech, but obviously requires power (exact type depends on model, but you should be able to look it up).

[Ken Layton]

Bill acceptors are a whole different breed, but in game applications they are NOT changemakers. When you put a bill in your are buying non refundable credits toward game play just as if you put 4 quarters in the machine.

Before 1996 there were no standards for bill acceptors. Everything wired different between different makes & models. Even connectors were different. Models like the Rowe OBA and Ardac MBA required a seperate control box to operate. Modern post-1996 bill acceptors usually conform to either Mars Electronics or CashCode standards for mounting, power connector, and interfacing standards. In general a bill acceptor (or it's control box) has a relay inside it. This relay has a set of contacts that you connect either in parallel with the existing coin switch or to coin switch #2 input on you gameboard. Either your bill acceptor or it's control box has dip switches that you set for the number of and duration of the pulses output. Example: If you are wired in parallel with the existing coin switch you set the dip switches to have the bill acceptor output 4 pulses per dollar (each pulse representing a quarter).

There are many early bill acceptors out there still working but they may not be upgradeable for the new $5 bills.

In my opinion the best and easiest to repair bill acceptor is the Rowe OBA. Even though that model is around 25 years old it was in production for a long time and Rowe still supports it! They even have an upgrade retrofit kit (cost $50) to allow it to accept the new $5 bills). Belts and parts for it are plentiful and frequently on sale.

The best bill acceptors made currently are Mars and Cashcode if you want to buy brand new. Mars are very expensive, though (in the $400 range).