I went to collimate and found that the whole secondary mirror assembly rotated!!
Oh my gawd!
This is not very good for collimating, because I know that the mirror has to be in a particular position in respect to everything else on the scope.
I posted a message onto the Cloudy Nights "Cats & Casses" asking for help, and got a reply back straight away from 'Uncle Rod Mollise' telling me how to take the corrector plate off to tighten the assembly. Thanks Rod.
Sleeping on it though I thought I'd have a go another way.
I thought that if I could pull on the assembly whilst turning it in a clockwise direction, it might just catch enough to tighten... and guess what? bingo! it worked.
All I had to do was make sure that the assembly was aligned correctly and I would be back in action. I just need to re-collimate ;-)
Here's a picture that I took a couple of years ago showing the correct orientation with respect to Bob's Knobs (NB. I think the indent positions pertain to my scope only, looking at pictures of other scopes, the positions vary):-
Corrector plate removal instructions. (In an emergency do not break glass)
1. The corrector must go back on in the same rotational orientation as before USUALLY the small, engraved serial number on the corrector goes to three o'clock. Maintain the original orientation of the secondary holder.
2. If there are shims present around the edge of the corrector, these must be replaced in their original positions--mark 'em.
3. When you are done, do not tighten the corrector retaining ring too tight--just finger tight.
4. DON'T BREAK THE CORRECTOR AND DON'T DAMAGE THE SURFACE OF THE SECONDARY!