Microwave looks and sounds like it is working, but won't heat. Any suggetions? Model # JES738WH001. Thanks

I would say 90% of the time it is a bad magnetron or transformer. You should have a qualified tech check it out. Microwaves are dangerous to work on if you are not qualified.
BigJon

90% of the time it is a door interlock, top or bottom (the middle, if there is one, is usually a safety interlock that blows a protection fuse that kills the power source so that the Mic won't operate with the door open)
Sometimes and interlock assemblt has slipped out of alignment from use and can be realigned by loosening, closing the door and pushing into place until the small click of the switch is heard when it comes in contact with the door hooks (should be at least three separate clicks when latch is closed very slowly.
Often the small switchs are mashed and have to be replaced.
Listen when you run it. The fan and turntable/or stirrer run but there is no deep hum a few seconds after the unit starts, and no power surge that dims the light a little and vibrates the unit. That means the mgnetron hasn't started. Magnetrons are expensive and fairly indestructable compared to other components. They come with a five year parts warranty but they are the last thing in the heating circuit.
One interlock controls a control relay or control panel circuit that sends power to the high power side. That could be your problem, or a relay or control board, which could mean a control panel replacement - also pricey but boards are rebuilt and parts and service outfits get as much as 50% off their purchase price if they return a board for a new or refurbished one.

If you smell insulation, or if you inspect the back hi-power supply, youu may find a burnt or failed power diode (very common). This provides the buildup of voltage in the voltage doubler circuit. It is paired with a can capacitor that will pack a wallop if you don't discharge it to ground (of course, this is all done with the unit unplugged. The can cap could be bad (check for short to the case, otherwise it should rise and fall across the poles). The big tranformer could be bad. It would blow fuses if it was short to ground, but check the coil for continuity. Again, it is unlikely to go, compared to the interlock alignment or failure, the diode and the control board/relay.

I'm a noob here with a similar problem as the original poster of this thread.

GE Sensor Convection, JVM1190AY

I have troubleshot the unit and the fuses are intact. I went straight for purchasing a new Samsung magnetron.

Any more advice available for divingh into this machine? I have 15 years experience in resteraunt equipment, HVAC, automotive repairs but, have never taken on a microwave...

Besides the interlocks, and the HV section (cap, diode, txfrmr), there is a thermistor on many units (I'm not directly talking of the GE sensor convection, but probably it has one). This shuts off the control circuitry to the transformer for the magnetron if it is heating up.
Problem might be: obstructed or inoperable fan motor, slipped or blocked cowling duct, vanes of fan (or stirrer in models without a carousel) slipping or off, bad thermistor.
Again, discharge the HV, check for voltage coming in to the txfrmr.
If not there, check the thermistor, if there's one on the circuit diagram.
A bad magnetron will make it overheat, but that is last in the process (and least susceptible, though more prevalent in commercial and public use venues).

Thanks. Ill download a wiring diagram (hopefully) and take the unit into the garage for further troubleshooting before I finalize the magnatron order.

I also have similar problem with my GE Spacemaker XL1800 (over the range).
I do smell a burnt odor, so is it the diode?Are they easy to replace?Any pics or guides?
Thx