Try to clean the round steel guides of the laser head. Use a very fine oil and remove all dust/dirt.

I'll give that a go tomorrow. I have replaced the laser so that bar is definitely clean, do you think it could be lacking oil/grease?

Yes. There is a plastic/bronce bushing guide inside the head. Without some oil/grease it becomes sticky. Clean it first with some alcohol, then use a fine oil. I use a oil for lock cylinders of doors.

I tried that this morning no improvement. The head is linear, and the guide rail has been recently removed and replaced as part of the renewal of the laser head assembly.

The disc now reliably spins for a couple of seconds and stops, and has not read the toc since it was recapped. I am trying to deduce the stage it is reaching before failing and it seems that :-

It establishes a disc is present

corrects focus height

spins disc and attempts to gain tracking.

this is the point where it fails, so it could be :-

failure in tracking logic or insufficient spin speed to successfully track.

I'm now looking for a motor!