Microwave - Not Heating / Please Help

[spidercharm]

Hi All, 

Whirlpool microwave / oven combo - cabinet mounted (Model # GMC305PDS07) . Few weeks ago, microwave stopped heating. Display, timer, lights, turntable etc. works fine. 

I have seen several videos, studied the circuit diagram carefully and did troubleshooting for all the parts - switches, diode, capacitor, magnetron, fuse etc. and they all seem to be okay.

1) Transformer (when removed) is testing fine on it own. Less than 1 ohm across the terminals and no shorting with the body. 

2) Transformer (terminals removed from transformer), I can see 120v coming in primary input terminals. I think this means circuit board and switches are fine. Note: I see 120v at input terminals even when microwave is not running - not sure if it's supposed to be that way. 

3) When transformer is connected, I don't see 120 v input coming in to terminals. This tells me transformer is shorted (based on 2 above). However, I have no idea if something else could be wrong (because transformer is testing fine on its own as I mentioned above). 

I have spent 2-3 weeks on it and would greatly appreciate your help. 

Transformer is one of the expensive part, so wanted to make sure I am not missing anything before ordering replacement. 

Thanks in advance.

[KaveMan]

Somethings amiss...you shouldn't see 120v at the primary side of the transformer if the unit is off. You sure you measured right?