I've got a head scratcher here, looking for an assist. I have a model PE4000-60, which would travel very slowly. I checked it out and found a bad drive motor brush. No problem, replaced the brush and sent it on it's way. The next day it came back with weird travel issues. Sometimes it would plug ok., sometimes not. sometimes when I changed directions, it would keep going in the same direction. When I brought it in to troubleshoot, I noticed a humming sound from the drive motor when the handle was up and no requested travel. The humming noise was as if the drive motor was being pulsed. it would hum for a couple seconds, then stop, then hum for a couple seconds, then stop.

This happened three or four times, then the motor controller burnt up. Actual smoke coming from the controller.

everything checks clean electrically, no shorts or grounds. I put a new motor controller in and also put a new drive motor in. when I pull the handle down and the line contactor comes in, the drive motor humming sound starts again. I unplugged the truck to keep from smoking another controller.

Any ideas??