On my Advantium 120 unit, the fan has one speed, high. Is there a way I can tell if the switch is bad or the motor is bad.

Generlly uWave oven fans have sevealr speeds. They are accomplished with an electronci speed control device in the form of a "Triac." That is a solid-state device that can fail sorted, which means the fan will run continuously on "high." It means the uWave oven needs a new controller, which will be expensive.

door switch is bad or out of adjustment I have a dometic that does this sometimes I just slam it a little harder

The door switches should be checked, often food partical buildup will cause one or more to malfunction.

The Turn Table motor needs to be replaced in the oven, this will require dis-assembly to get at the part, and please remember there is dangerous high voltage present if you are going to do the work yourself.

It sounds like the magnetron may have either failed or is not being supplied with the extremely high voltage required to run it.
Make sure the !!!!capacitor is discharged!!!!! before attempting any sort of repair.
Check the door interlock switches first then the high voltage diode with either an AVO model 8 on high resistance range for short circuit, the capacitor can fail and go short circuit, the feed fuse on the primary of the high voltage transformer and then finally, the magnetron is best checked by substitution.
Hope that helps.

Is there any unusual noise or is it louder or quieter than normal?

A loud buzz, hum, or groan is usually a shorted high voltage rectifier diode, but a sound like gurgling into an empty coffee mug is one symptom of a failed magnetron, and yet the mag can be bad without that sound.

We have a sound clip of what a microwave should sound like when the cooling fan and high voltage section are working.

If it sounds the same as usual or a little louder, I would suspect the magnetron or high voltage diode has failed.

If it is much quieter than usual I would suspect a bad upper door switch.

The service manual is here.

Also see this file on door switches.

You have a bad cavity switch. I would guess it is the one behind the vent cover, toward the left side of unit. You would need to remove unit from wall. Remove outer housing to expose cavity switch. You can see it from vent cover, I would test all cavity switches before removing from wall. You should have a diagram of unit folded up behind vent cover towards right side of unit. This tells all workings of unit. Will also tell where all cavity switches are.

remove the cover ... look on the floor of the unit near where the cord enters the cabinet.

This is a dead magnitron tube, You can fix it yourself.First order your part at marcone.com with your model #. When you get it you will need to pull the unit down and take off the case to switch the mag tube.

You have a bad door swicth or a bad wiring connector to one of the door switches... secondary swicth or the door sense switch.