Troubleshooting Jenn-Air Double Wall Oven

We had a power outage last November which caused my mother’s double wall oven to go "black" when the power came back on. Electrician came and determined everything was fine electrically with the ovens. Didn’t have a chance to repair it. Four months later the oven magically started working again! The display was dimmer but both ovens functioned fine. Power went out again last week…ovens are dead again. I’ve turned off the circuit breaker for 20 minutes and flipped it back on and nothing happened. Please help! Thank you!