Accidentally pushed the drum-tray back in without the drum? The green light won't show, and the tray won't budge - all you need to do is to carefully push a tiny lever below the tray, as pictured.
What to do if you have drum stuck in your RP 3700 that is not in the right position.
Original article: http://www.drucksalon.ch/828/how-to-remove-a-stuck-drum-from-a-riso-rp-3...
Procedure for converting the color of a Z-type drum. Steps 1 - 9 also work when machine does not recogonize a correctly installed ink tube.
There are several Risograph z-type drums, most of which are not universally compatible. Use the following charts to determine compatibility with your machine.