GE JVM3160RF5SS trips breaker on start

[Kvothe71]

Lights are on and can set cook cycle but breaker trips immediately when I press start. Swapped breaker for new and same issue. 
Troubleshooting done:

Fuse continuity good. Three door switches pass appropriate continuity tests when door is open and closed. Capacitor measures fine. Did a simple Magnetron test across posts at less than an Ohm and is open from post to magnetron body.

Two things test bad - the Base thermostat and possibly another thermostat but I cant identify it. It doesn’t have continuity but I dont see anything saying what it is. It is in the top cavity that contains the fuse and is on the left side attached to the blower assembly with 2 posts. Does no continuity mean this is bad and if so, what is it and how do I access it?

Lastly, are there other potential causes I havent tested?

 

Thanks!

[Vance R]

26 minutes ago, Kvothe71 said:

Lastly, are there other potential causes I havent tested?

If you feel comfortable do this try unplugging one of the 120 vac wires to the HV transformer. Make sure it does not touch anything or insulate with electrical tape.  Run the microwave - if the breaker trips you have something in the 120 vac side of the transformer cause your issue with the breaker. If the breaker does not trip your issue is on the high voltage side of the transformer - cap, diode or mag and silght possiblity of the HV transformer.

Some thermostats in a over the range microwave are open at room temp. They close when things get to hot and turn on vent fan for safety.

[Kvothe71]

Thanks. Confirmed it was on hv side and retested cap. Forgot to tests posts to the body and it failed. Thanks for the tip!

[Thanus]

Good morning .. ultimately did ? and if so how did you repair unit. I’m still green to appliance repair. I have no on hand mentor and all my learning will be hands on ALONE learning. Trying to grow as I go. Job this week same issue would like to complete job, then reverse engineer the learning curbs at home of theories and procedures. I know that sounds crazy but I have a family of 5 with full time job so this works for my lifestyle currently. Looking Togo Appliance repair full time within next few months. Thanks for any assist in advance.