Thanks for the replies :-)
The drive is the later Philips type, with straight-line tracking. I checked the transport screws, they were in place and were fully unscrewed.
I removed and dismantled the CD drive, then cleaned the lens & mirror as per:
https://www.youtube.com/watch?v=qXGubkovMEE
The lens and mirror actually looked quite clean. There was no hardened grease on the tracking drive, and everything is moving freely, including the pickup along the guide rail. No bulging capacitors, or any other visual anomalies on the two boards.
Reassembled, and it's still no different, returning error 2 when pressing CD in Test Mode. Before reassembly, I manually moved the pickup to the outer most position. When pressing CD, the pickup moved to the inner most position, so it's fair to say there is at least power! The spindle motor hasn't once moved though, not even a blip.
I am wondering if someone has been in here before... One of the four screws that secure the drive mechanism to the steel chassis is silver, the other three are black. I could also see what appeared to be some telltale wear to the coating on the black screws.
@billbriscoe I agree, they are great units! I was mightily impressed with the first one I acquired. I've just never really noticed the Century before now, thinking (erroneously) they wouldn't sound that great. How wrong I was! My Mother who's in her 80s is now enjoying her expanding CD collection. It's easy for her to use, after I made up some cheat-sheets to guide her :-)