Thanks David,
The drum is not moving at all at the moment. It tries to do the normal start up process which involves rotations and various noises but it gets no further than what seems to be a failed initial two attempts at rotating which is indicated by two fairly quiet and soft thumps which seem to suggest the drum cannot (is unable to) rotate.
The black cog is on its shaft and meshing with the hollow arm from the top cover. The external teeth to this top cover hollow arm and thus the arm itself move up as the cover is opened and down as it shuts. At its uppermost the little cog has its flat face vertical at the front. I have removed the cog and the shaft will not rotate anticlockwise anymore which confirms that the white part to which the shaft itself is connected is fully up. I attach an image in the top cover 'up' position.
I will disassemble and replace the adhesive chair foot pad with some velcro. As a matter of interest:
a) How thick was the original pad? What was left of mine was about 1mm (1/25th inch). The felt pad is about 3mm. This means that when the solenoid is actioned the two hooks on the end of the solenoid lever do not withdraw as much as they did. Clearly I have achieved something as the nature of the problem has changed from a rotating, but noisy thumping drum, which only seems to print part or all of a single page, to a jammed printer!
b) What is this optical sensor fault I get on the print dialogue page and can I have affected something else? For example, is it possible that one of the four cable I had to detach is not re-located properly (although they looked and felt OK)?