Thank you Marco. I've checked just about everything. I ran both the hydraulic and drive motors. I've checked all 4 diodes (both blocks) with a Handyman. Checked all contractors and sent the main card out for testing and repair. I checked all power cables. The only thing that hasn't been checked yet is the rubber insulation sheet under the transistors. I mean I checked the heat sink for short to chassis with an ohm meter, but not with the Handyman. I know Clark's use to get pin holes in that sheet causing shorts. This thing is definitely a problem child. But thank you for chiming in. I already burnt up 2 new transistors. They blow on the self diagnostic check.