Just in case anyone is interested, replacing the failed Darlington
transistor fixed the problem. The RD53 now spins the disk again. Thanks to
everyone who helped.
Some people enjoy repairing things. I find it a bit of a drudge.
What I enjoy is the feeling of satisfaction when a repair succeeds :-)
Well done to all involved.
I am now looking with renewed interest at my pile of doorstops which once spun.
Regards,
Peter Coghlan.