Frigidaire OTR not heating - advanced tests needed?

Microwave Repair
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1

Hello,
I have a Frigidaire PLMV168CC1 over-the-range microwave purchased and installed in about 2004. Recently the microwave stopped heating. All functionality when attempting to heat works as always (display, timer, fan, light) and the only symptom of the issue is that no actual heating occurs. I have already done a substantial amount of testing to include:

  1. Confirm all three door interlocks function properly.
  2. Test HV diode (I replaced the diode as I initially thought this might be the issue and they are inexpensive). Turns out the original diode is still good.
  3. Test HV capacitor (as much as possible using digital Fluke 87 meter with analog like indicator to see charging and discharging with two 9 volt batteries)
  4. Test all thermal switches and confirmed NO or NC per the schematic located within the appliance.
  5. I have measured the resistance of primary and secondary windings of the HV transformer. The secondary side was ~5 ohms higher than spec. The primary side was normal.
  6. I have measure the resistance of the magnatron and it measured what what was suggested on multiple internet sites.
  7. Finally, I can confirm that when I attempt to heat there is 120VAC at the primary side of the HV transformer. I have to tool capable (nor do I want to) of measuring the secondary voltage of the HV transformer.

Questions:

  1. Am I correct in assuming that the issue is either with the HV transformer or the Magnatron (since I’m getting 120VAC at the HV transformer primary)?
  2. Would a useful HV transformer test be to connect a lower AC voltage (from a doorbell transformer, etc.) to the primary side so I can measure the secondary side?
  3. What else can I do to troubleshoot?

Note: I was ready to write this microwave off and purchase a new one until I discovered that all the new OTR microwaves vent (at least the microwave portion, not necessarily the range hood) from the top. This microwave and most others from this vintage have front facing vents on top. Our kitchen cabinet directly above the microwave is approx. 19" deep. All of the current microwave require a max cabinet depth of 12 or 13 inches and we don’t want to butcher our cabinets or mount the microwave 6-7 inches from the back wall. So… although this will eventually be an issue I am motivated to fix this! Thanks in advance for any replies and advice!