I bought in the states a brand new microwave/convection hood combo which I delivered to my country in south America a couple of weeks ago.

Yesterday it just started to make a quite louder than before humming and noise when microwaving and it doesn't heat the food at all.

Everything in the control panel is working, it display sensing in the preset automatic modes and displays the elapsed time when in manual.

The convection mode is working fine. Unfortunately the unit is still under the full year warranty, but sending it back to the states for a in home warranty service repair is out of question because it will cost me a lot more in shipping expenses of what the whole oven is worth.

My older Whirpool microwave/Hood combo came with a troubleshooting guide inside a bag behind the control panel which help me a lot in the past when I had to pinpoint a faulty door lock switch but as far as I know this newer one didn't have one.

I called the bigger appliance parts supplier in my country which deals with Whirpool and his manager, who is a close friend, told me this oven is quite new and has not been imported and sold here yet.

I am a retired broadcast engineer and had a lot of experience with electronic devices, so I can replace any part but have no idea how to check if the magnetron is faulty, besides the fact I don't have the oven troubleshooting guide or schematics to help me.

The replacement magnetron cost plus shipping to my country would be less than $100, which is way better than waste the oven at all but I need to be 100 % sure it is bad before ordering the part, which by the way I found is the same used by many other brands and models.

How could I check if it is bad or what else could be at fault and causing the microwaving problem ?

Any help will be deeply appreciated

Still a work in progress, can only when my people let me free to do the tests.

I know everybody is afraid and against H/V measures but been familiar with the subject I hook a Fluke 1000:1 40KV high voltage probe to my auto polarity DMM ( my old Simpson analog multimeter is not banana plug compatible with the probe) and did the following tests with the Microwave oven hooked and a glass of water:

1) Working now with the High Voltage transformer, I measured A/C voltage between the secondary ground and the secondary wire which goes to the capacitor input and got 2650 VAC which under load is quite well over the theoretical value of 2800 VAC so I guess at least the transformer seems to be fine.

2) Then I measured the DC voltage at the capacitor output which as you know goes to the joint point of the positive side of the diode, one of the H/V transformer secondary winding filament outs and one of the filament inputs of the magnetron. It measures 130 VDC instead of the of the desired under load value of about 5300 VDC.

3) Now I unhooked of the magnetron the black and red jacketed wires which goes to it's filament wires input and did again the tests which surprised me a little bit: I measured about 2100 VAC at the capacitor input and around to 3250 VDC at the capacitor output.

I don't understand why under no magnetron load the A/C volt drooped a bit and didn't have a quite bigger DC higher voltage which I guess should go up to more than 5700 VDC !!!!!!

Again if any body with experience fixing microwaves could give me a tip, it would be great because I need to order the parts and they would take time to be delivered to my country and still have the appliance all disassembled over the dinning table, my wife is just so close to kill me, and she is more dangerous than the microwave H/V output !!!!!!! :D