The truck is about eleven years old and although in a very clean and straight condition may have been misused from time to time.
I'm inclined to agree with tom w with his opinion that the battery voltage may have been low or the truck was used to push some equipment.
At the same time I'm puzzled that all of the heating is in the inside of the controller and nowhere else and was trying to reassure myself by trying to find out if there was an internal problem with these controllers.
Anyway at this stage the controller has to be replaced and the owner has deferred repairing it because of the cost.
Many thanks to everyone for your opinions and help.
Where did the source of heat originate? If the controller cover is badly burned around a power terminal, the burnt controller could be due to a loose cable connection. If the cables aren't torqued down to spec, this could cause an intermittent connection or not allow full contact, which would increase the resistance of the joint, thus increasing the heat exponentially.
If the cover is not burnt around any terminals, but the damage was confined to the inside of the module, I would suggest sending it back to Crown for a failure analysis. That should shed some light on the failed components and the possible cause.
Your description would lead me to look for a low voltage and/or high current problem.
Maybe like operating the unit with a low battery or pushing with it. Most units these days have low voltage cutouts on them, but, sometimes they are not adjusted correctly, have failed completely or have been bypassed.
Is the truck protected against static electrical discharge? Have seen many GE controllers which fail because of static electricity.
Nice to see all the crown guys jumped right on this to help you out!
I'm afraid that I have ZERO experience with that controller so I can be of no help at all.
Except of course as a smart-azz :-)