White countertop microwave on a kitchen counter
6 components covered

Field manual · Microwave

Panasonic NN-SN966S / NN-SD975S inverter microwave: quick sheet

Covers: Panasonic 2.2 cu ft, 1250 W countertop inverter microwaves: NN-SN966S (stainless, Genius Sensor) and NN-SD975S (Cyclonic Wave inverter), widely sold 2016 onward (Panasonic spec page; Consumer Reports; retail listings).

Single sourceBrands: Panasonic6 components

Large countertop inverter models and among the best-selling microwaves in the US. Instead of a heavy transformer and HV capacitor, an inverter board drives the magnetron and allows true low-power cooking. The famous failure codes are H97/H98 (inverter/magnetron circuit) — expensive parts, so diagnose carefully.

Safety first

  • Unplug before removing the outer wrapper; never run the oven with the cabinet off.
  • The high-voltage capacitor (transformer models) or inverter board can hold a lethal charge after unplugging: discharge per the service data with an insulated, resistor-type tool before touching anything.
  • Never measure live high-voltage circuits; all HV component tests are done powered off.
  • Door switches, interlock and door seal must be correct before return to service; a misaligned door is a microwave leakage risk.
  • If the oven arcs, smokes or shows burn marks in the cavity, stop and inspect the waveguide cover and cavity paint before reuse.

How it works

The control board reads the keypad and humidity sensor, closes the door-switch chain and relays, and commands the inverter board, which converts line voltage to high-voltage DC for the magnetron. Power level is set by inverter output, not by on/off cycling.

The inverter reports back to the control. If the expected feedback or oscillation is missing (H97) or an overload/overheat is detected (H98), the oven stops and shows the code. Repair sites report the control may lock the oven after repeated events; that claim is single-source.

A cooling fan pulls air across the inverter heatsink and magnetron; blocked vents and a dead fan cause overheating trips.

Components & tests

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Official manufacturer documentation

Always confirm values against the tech sheet for the exact model.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work. © 2026 OnCall Tech. Original content; not a reproduction of any manufacturer document.Generic part photos (not of this brand): White countertop microwave on a kitchen counter by cottonbro studio, Pexels License

Diagnostic guides for this appliance

Component test · Microwave

Magnetron: filament and filament-to-case tests (microwave)

The magnetron turns high voltage into microwave energy. An ohmmeter can catch an open filament or a filament shorted to the case, but it cannot prove the tube makes full power. Rule out the HV diode, capacitor and transformer before ordering a magnetron.

6 steps ~40 minadvanced
Component test · Microwave

Microwave high-voltage diode test

The HV diode works with the HV capacitor to double the transformer voltage for the magnetron. It is made of many junctions in series, so an ordinary meter only shows it is not shorted. A shorted diode is a classic cause of no heat with a loud hum.

4 steps ~20 minadvanced
Component test · Microwave

Microwave HV capacitor and bleeder resistor

The HV capacitor has a built-in bleeder resistor meant to drain its charge, but bleeders fail, so always discharge by hand. A shorted capacitor blows the HV fuse immediately. Resistance tests catch shorts; a capacitance reading is better.

4 steps ~20 minadvanced

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Inverter microwaves (Panasonic, LG NeoChef and others): field service manual

Countertop and some built-in microwaves that replace the iron-core transformer with an inverter circuit board: most Panasonic models (marketed as Inverter), LG NeoChef Smart Inverter, and inverter models from other brands. Confirm by looking for a finned circuit board in place of the heavy transformer.

4 components4 common failuresPanasonic, LG, Others with inverter power supply
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Over-the-range (OTR) microwave: field service manual

Microwave/hood combinations hung on a wall mounting plate under an upper cabinet above a range. The cooking section is a transformer (or, on some models, inverter) microwave; this manual covers what is different: vent fan, damper, cooktop light, filters, installation and power.

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Panasonic NN-SN966S / NN-SD975S inverter microwave: quick sheet · OnCall Tech