Update: no luck. Looks like I'll be calling George for options.
>>Here is how you can test whether one of the two motors or encoders might be non-functional. Plug the short part of the Y cable into the RA motor box. Turn power on and push the E-W buttons at 600x (do not push N-S buttons). If the motor slews properly, then it is good, and your R.A. Y cable connection is also good. Now plug the short end of the Y cable into the Dec motor box. Turn power on and push the E-W buttons at 600x. Again, if the motor slews properly, then that motor circuit is also functioning correctly.
The short part of the cable was already plugged into the RA motor box. The behavior was unchanged - the initial quick slew, and any push of the E-W buttons results in a very quick slew, the mount freezes while I'm holding the button down, then the west slew resumes when I let go.
The short cable couldn't reach the DEC motor housing, so I had to plug the long end of the Y cable into the controller. Don't know if that messed anything up; either way the Dec motor was unresponsive.
>>Try this first and see what happens. Best to call George here during the day and he can walk you thru any further tests. In any case, the mount is modular, and we can repair any portion without you having to send the entire mount in.