I don't have one of those, so all I could offer would be some general guidelines.
If the unit is old or well used, I'd start by checking the motor brushes.
If the problem is in one direction and not the other, I'd check the limit switches and directional switches.
Otherwise, just do a general check for loose wires, etc.
If there's a section of cable that flexes "tightly", or if there's a kink, I'd suspect a broken conductor inside the cable.
I kinda doubt that an intermittent problem would be do to fried electronics, though I suppose a poor solder joint on the PC board might be the cause - luckily, that's something you can usually find by inspection.