Over the last couple of days pulled apart MIXA #2 to diagnose the problem, Both MIXA's have bung "ON" switches, but the failure modes seemed a little different, so I figured maybe I had enough parts to get one going. I can get new switches online, but was not sure which part is broken/fried.
The failure was simple, the selector dial has a blade on it on the inside that operates the "on/off" switch, and my blade had broken off. I pulled apart MIXA #1 and it's selector dial is intact. I transplanted this part into MIXA #2 and operations are normal. I make a mental note to be gentle on the selector dial, but new parts are available.
I also discover the contact inside the switch on MIXA #1 was jammed due to some carbon scoring. After cleaning and lubricating it is working normally too. I use a youtube hint and fix the broken selector dial with superglue and baking sode, and MIXA #1 is now working fine also. MIXA #1 now rests honorably in stand-by storage, and MIXA #2 is back in service! Win Win. No pictures.