Swapped a bunch of components (flyback, vertical sync IC, horizontal deflection IC), tested HOT, replaced the mofset. Chassis worked fine plugged in from a Motocross Go cab until I unplugged the chassis (from the power plug at the chassis) while the cab was powered on. A voltage arc happened somewhere in the chassis killing a part that can only be obtained from another chassis (or something else).
Namco cabs like these were probably designed for something NOT to be unplugged while powered on and using components as a test bench from the cab was probably a big mistake.