Technobeam : Litho disassembly problem

Hello, I'm french and I own 6 Technobeams since a few days. 2 of them had the "LTR SENS ERR", but that wasn't a problem of sensor, because the litho rotation motors didn't work at all.. I have others motors that I can use to replace the defective ones, but I don't understand how to get out the gobo/color block ? I don't see any screw that I could unscrew.. Could you tell me how to do ?

Thanks a lot

Olivier
(excuse me for my poor english)
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