(ET) My E-15 motor controller has broken!

[cleanair mail2 deniz com]

After about a year of faithfull service my E-15 has motor driver has
failed.
   I have probably ignored some warning signs:

  1.  The control of the motor has been somewhat "jerky" lately.  More
apparent in the lower gears.
 
  2.  Reversing, sometimes doesn't work, unless you come to a complete
stop, and wait for a couple of seconds. What happens is the instead of
reversing, it drives forward until you step on the brake.

  Problem 1 seemed to occur more with the mower on.  I was thinking that
this might be related to the varistor shown in the manual pg 1-33.  The
varistor is to prevent in-advertent triggering of the SCRs.

  My current problem happened yesterday when I was towing some logs with
the tractor.  The log got stuck and stopped the tractor from moving
several times.  One of these times I pulled the tractor backwards, by
pulling the tow cable.

   After this putting the control in forward or reverse only results in a
lot of relay chatter, and no movement.  It breifly moved once after this,
but then stopped again with the relay chatter again.  

  Do these symptoms suggest anything obvious to anyone.  I am about to
embark on a troubleshotting session using the manual as my guide, but
thought I would ask here first, in case anyone has been down this road
before.

  Thanks,
    Matt O'Brien