I have owned as many

Question

I have owned as many as 6 Sharp convection Microwaves, they have all suffered the same fate. The timer when in convection stops at approx 5min in this time it has not heated hot enough and each time is reset it will work again for another 5min. If on duel power it stops on convection but works on microwave. It cost about $80 plus to repair depending on who you take it to. I have 4 units with this problem at this moment. My Sons, sisters a rental as well as mine. Can you help identify the part that causes the problem. Can you inform Sharp as I beleive they should have attended to this issue but the same moduel is in different models. Yours Sincerely Terry Dowsett