Microwave shuts off intermittently, already replaced door switch assem

I have a model 401.80082700 serial 725MM00044. Intermittent problem. Microwave goes through heating cycle and then totally powers off…no display, no light, no power. After 15-30 seconds the display comes on and instructs to press clock and reset time of day. After doing so the microwave is fully functional and may operate several times before powering off again. Occasionally the display appears fainter than normal, esp the center of display. I have replaced the door switch assembly but after several days the intermittent problem has returned. What do you think? TY