[Towertalk] HAM IV strange defect

[Roger]

My HAM IV rotator has a strange failure.
One night I turned on the control box and tried to turn the beam (a single 
Force 12 C-3, nothing more). It did not turn (the needle did not move and 
the antenna really did not move too). I tried to rotate to the other 
direction. No operation. I gave up. A month later, without touching 
anything, it worked again. It kept OK for, say, two months. On a given 
night it stoped working again. One week later it came back to life. Then 
after a month it stoped working again. This cycle repeated several times.

When I had the chance, during a "stop", I took it from the tower. 
Before  disassembling it, I connected it (in my garage) to the control box 
using a short piece of cable. It worked perfectly... I left everything 
assembled in the garage and some days later I tested it again. The rotor 
did not turn. I disassembled it, but I did not find any signs of damage. 
Even the break wedge seems to work perfectly. In resume, the rotor simply 
keeps this strange behaviour but, inside it, every piece seems brand new.

Has anybody already experienced this kind of failure? Assuming that the 
cable is not the problem, may I suspect of a problem in the control box? 
What components should I investigate?

Your advice will be much appreciated.
73 de Roger, PY1OL