Ok the system is fixed, took a few hrs but testing takes days!
Turns out the DEC H bridge was dead and when I replaced this the DEC motor did un-commanded slews. Swapping the DEC to RA etc the fault followed the motor. Replacing with my motor, all was good.
I did some fiddling and found the DEC motor had a bad encoder, as compared to a good unit (some funny ohm meter measurements, though I have no cct diagram of what's in the encoder). I had a 2nd hand encoder so I replaced this and the motor is fixed. No more un-commanded slews or uncontrolled runaways.
Now the original fault, a few years back, was a dead RA H bridge. I replaced this and all was good. But it looks as if the motor (or one motor) had intermittent fail in the encoder and years later when re-assembled, it burnt out the DEC H bridge (the motor was assembled to the DEC channel this time).
Obviously this was the original fault years back but was intermittent as it passed all my tests (a few days of testing), Lester tested it ok and packed it away. Reassembling it a years or so later it killed the DEC channel as this intermittent fault came back but this time the motor was on DEC. At least this time it had a hard fault so I could go hunting for it. Well that's my story and I'm sticking with it!
Lester is lucky as a replacement motor would have cost ...a lot. Lester has the Maxon motors.
I love these motors.
I'm also thankful Lester sent it back to me as I had the history of this unit and was more critical in approaching it.
Tickets anyone!
