Arcing In Wave Guide

[Jon Myres]

recently went on a service call for the new Whirlpool slim fit microwave (WML75011HV1). Compliant was no heat and after doing some test I determined the unit needed a new magnetron. After replacing the magnetron the unit heated water, but started to arc through a small screw above the magnetron in the metal wave guide. Checked the screw and it was loose and could not be tightened. Called tech support to find out what this screw does and got nowhere other than deemed non-repairable. Anyone know what that screw is? Why it could be loose and why it’s blowing mags?

[johntech]

If the wave guide is damaged it is not repairable because it is part of the cabinet. Not sure what screw you are referring to and they do not show the cabinet on the break down to reference. If the magnatron is arcing it will fail. Any time I run into bad magnetron I use a mirror to look into the wave guide for damage from arcing, if it is damaged then the microwave would need to be replaced. Microwaves are attracted to sharp metal edges so I can’t see any reason a screw would be in the wave guide. If the screw would not tighten then most likely it became very hot and expanded or burned the hole larger. So that explains why the screw is loose and why it is blowing mags but I can not tell you why the screw is there in the first place or what it does. I have worked on that style many times and have never noticed a screw in the wave guide.