I disassembled the controller and tested the CM600 IGBT, and it was OK. Tested it with a 12V lamp, and it turned on and off with the gate trigger. Great!
I set up a 24V supply and wired up the controller to a temporary brake switch and throttle potentiometer, and it was working also.
I put the system back together on the bench with a 12V DC brushed motor, and the motor spun up and down with the throttle.
Now I'm confused, because the system was dead on the kart, but now has risen on the bench. Either a miracle has happened, or I have an intermittent problem.
Maybe I had a battery problem ???? To be continued...