I have worked on the roboscan line for a while dealing with everything between the 1220,518,218 and the little 812. fixing them for DJ's and local night clubs. There could be lots of problems. Lets pin point this:
Did that fixture that was not powering up power at all? (did it start-up for a second then stop)
Did you check all the fuses? (if I recall there is a fuse on the circuit board as well, with that being said opening that light may get a bit dicey. I'll give you tips if we need to go down that path.)
Did the fan power up?
Open circuit will be the last thing to check. (This happens when 1 or more leads that carry power is open)
Are you running them in 110V-120V or 208v-220v?
The more info you can give me the better. Lets keep the old lights alive!![:D]