Two thoughts.

1. If there is something wrong with the logic circuits, the manufacturer should fix them.

2. If you've given up hope on #1, why not just remove power from the logic boards rather than from the entire appliance? That can probably be done with a $3 toggle switch mounted to a convenient location on the control panel.

With respect to #2, remember that any modification that you make to the appliance may affect its UL approval.

80 AMPS!? Are sure you don't mean a double pole 40A? Anyway, David has good ideas, but I would push Jenn-Air hard to make them right.

On the first point, the ovens are probably 15 years old, and when I did call Jenn-Air, they told me they never heard of such a problem. Their customer service sucked, to put it politely. We had the memory board replaced twice in each oven. The Sears repair guy said it was because of a power surge. Jenn-Air said this couldn't be true. So, we're out about $500/repair.

On the second point, the logic board also controls temperature and the timer, so it can't be disabled. I guess you're saying to disable it when we're not using the oven and enable it when we are?

On the third point, I don't care about UL approval. If and when we sell the house, we'll replace the ovens and microwave.

Yes, I meant a double pole 40A.

So, can I put a 30A switch in-line with the oven power supply and turn it off and on (safely) without running to the fuse box? Seems to me that if a 40A double pole fuse is good for an oven and microwave, that a 30A switch should be sufficient.

There is a switch on the front panel that controls the oven light, for when the door is closed. It is integral into the glass control panel. Can I just disconnect this, cut the power line to the control board, and use this switch to control power to the panel? This would then switch power on and off to the control board, while leaving the oven hard-wired.

Either that, or I can install a new switch on the side of the oven (the panel is glass, so I can't drill through it).

You guys are geniuses.

Your original idea to put a switch in the incoming power line is a lot better than the current direction this has headed - to modifying the oven itself.

60 amp double pole disconnects are readily available at places like Home Depot and Lowes for about $10.

Your comment that a 40A breaker indicates that a 30A switch is "sufficient" makes me think that you should hire a professional to do this work. A 30A switch might indeed be sufficient, but how you get there from seeing a 40A breaker is beyond me.

sbs9: If a 40A double pole breaker is sufficient for both a microwave and oven, then doesn't it necessarily follow that both the microwave and oven must each be less than 40A?

There is a 120V switch on the control panel that turns the oven light on and off when the door is closed.

There are two power feeds from the main 120V (black) line: one to the contacts for the oven and broiler coils and one to the control panel. I cut this second line, connected it to the (former) switch for the lights, and now this switch turns on and off power to the control panel. When we're not using the oven, the switch is off.

If you're going to replace the ovens when you go to sell anyway, why not go ahead and do that and enjoy using non "rigged" and non defective ovens now? What you're describing is a royal PIA to deal with and it's counter productive to deal with the defect rather than just replacing it.