Hi Johan,
I can say conclusively now that my problem is due to the failure of this flexible coupling. I used a few drops of crazy glue to re-assemble the original polyurethane insert. After it was dry, I popped it into position together with an O-ring to keep it together in case it let go again. I reassembled the encoder in the spindle motor, and voila! it powered up normally and the spindle now responds normally forwards and reverse.
Please be careful when you remove the encoder, I scribed a line on the body of the encoder and the spindle mount to be sure it is clocked in he same orientation when it is reinstalled. the encoder is held on by the three cap-screws on the underside of the spindle mount - I would not recommend removing the screws on the top cover. Also, the button head screws holding the perforated cover were a PITA to remove - I stripped the Hex and had to use a chistle to free them up. I think they must have been secured with Loctite.
The Flexible coupling is NOT listed or pictured in the parts diagram. I could read the insert had the name "ROTEX" ; what found when I searched for this is that this is likely a Rotex GS series coupler and the size seems to be a #9 (GS9)... the broken flexible piece is referred to as the "spider" and it can be replaced as a separate item.
I should also give some of the credit for my success to a member of another CNC forum who was very helpful in guiding me towards the faulty item.... Thanks WRENCH !!!:banana:
At this time if I were to consider a retrofit I would try to utilize as much of the existing components as possible. I'm not sure if I would use Mach3; I'm leaning more towards the Dynomotion Kflop.
I found a few videos of a guy who did a really nice conversion to Mach3 using all of the original motors, it seems all the functions are working (its not clear what drives he used, he said in one of the videos they were "Berger Lahr" to match the motors...) I have no association with this individual....I just like the way he did the retrofit.
-
https://www.youtube.com/watch?v=QldE8tRRR7E (Part 1 - I guess this is the before shot...?)
-
https://www.youtube.com/watch?v=EqpDUYT6Yuk (Part 2)
-
https://www.youtube.com/watch?v=6-GK3EKs6ZM (Part 3)
-
https://www.youtube.com/watch?v=ebzOxl6z3TE (Part 4)
-
https://www.youtube.com/watch?v=lRab4ic2hjQ (Part 5)