Microwave/Convection Oven has mind of its own: turns to Crisp mode on its own.

If you're sure the Magneton is bad, it's quite easy to remove and replace.

A convection microwave is a combination of a standard microwave oven and a convection oven. It allows food cooked in the convection microwave to be cooked quickly, yet come out browned or crisped as in a convection oven. However, most cakes cannot be baked in a microwave oven - only those without an open grain structure, such as brownies. There are microwaves which contain electric browning baking elements. A true convection microwave has a high velocity forced air fan to circulate the hot air uniformly.

more about Convection microwave

Try the directions on this site: Customer Questions and Answers for Electronic Control Board by Whirlpool

A loud humming noise in microwave mode will usually be a shorted high voltage diode or bad magnetron.

i don't have the manual of whirlpool magic cook 25c could you plz help me

Most likely needs a new magnetron

I have the same problem
any hints to solve it.
It's a 1988 vintage oven/microwave so I can't complain but it 's a pain if
I have to replace the unit

http://shared.whirlpoolcorp.com/product_literature/search_results.jsp?searchTerm=KEMS307DBS&siteCd=KAD#parts_list HEY ANDYCOOL,GO TO THIS LINK IT'LL SHOW YOU ANYTHING YOUR HEART DESIRES ABOUT THIS UNIT(DRAWINGS,USER MANUAL,PARTS LIST,INSTALLATION GUIDE,ECT.)SORRY BUT FROM THE LOOKS OF IT YOUR GONNA HAVE TO PULL THAT PUPPY.BUT YOU BE THE JUDGE OF THAT.GOOD LUCK,HOPE THIS HELPS!!!!

I would recommend changing the diodes as well. This will usually take care of the problem.

Thanks, I took it in for a 45 dollar analysis