Photoplay Bill Acceptor

My Photoplay Spirit 2.1 always had a working NV4 smile bill acceptor.
It's no longer accepting any bills -at all-. It takes them in about 1-2mm and spits them back out immediatly, so it's not that
it rejects the bills, it doesn't even try to scan it.
I've recalibrated it according to the manual (push the channel-button while powering on with a white piece of paper in it's mouth) and the paper goes in and out, fully works.

What could be wrong? Why isn't it accepting bills at all? The only thing I might have changed around is the configuration of the serial ports, but on the other hand I would expect it to work even if there's no serial connection, it just won't add credits then, but it should read it, doesn't it?

Sorry for the video being only 30% of the screen because of the ipod that took it, but here's the video: http://youtu.be/9-kLrPwR9oI