I have the same problem with my GE Spacemaker. I was told by an electrician friend (who is extremely smart) that the "magnetron" has failed. this is a Bulb unit which causes the microwaves when it heats up. to replace it would require soldering wires and buying the part which is WB27X10489 $138.00 alone with no labor. I cannot justify buying a $140 part on a 6 year old unit, and I cannot be sure that this will fix it or I won't damage it fixing it myself. There is also a circuit card on this unit which costs about 130$ so I will simply be buying a new unit for 290$ . Perhaps this is a problem with ALL GE Units? I'm starting to wonder!!!
Carl C., October 2006