As Dave says sometimes the filters can stick and not return into the light path. I've got two colour heads for the Mod70 and if I wind the filter a bit too much (e.g. just past 170) and switch the lever to "out", which is the white light setting, when I reset the lever to "in" the filter doesn't drop into the light path. It's the same on both heads and by just turning the filter control a touch the filter drops down.