4 components coveredField manual · Microwave
Inverter microwaves (Panasonic, LG NeoChef and others): field service manual
Covers: 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.
An inverter microwave still uses a normal magnetron, but its high voltage comes from a switching power board with a small transformer instead of the 60 Hz transformer, capacitor and diode. Power levels are made by varying the output instead of switching full power on and off. For the field tech, the practical rule is: the magnetron, door switches, fuse, fan and cutouts are testable as usual; the inverter board is a replace-only part diagnosed by the brand's self-diagnosis and service procedure.
Safety first
- DANGER: inverter boards and the HV output can hold a lethal charge after the unit is unplugged
- Untrained users must not open the cabinet
- Every internal step: unplug, wait, discharge with an insulated resistor tool, verify 0 V, then work
- Never measure the HV output or board voltages while energized; never jumper or bypass the magnetron leads (a forum test like that vaporized the jumper wire)
- Never operate with the wrapper removed or with interlocks bypassed
- Do not attempt component-level board repair in the field
How it works
Line power passes through the fuse, noise filter and door interlocks as in a conventional unit, then to the inverter board.
The inverter board rectifies the line and switches it at a high frequency (roughly 20-45 kHz, varied by the control). A small high-frequency transformer on the board steps this up, and on-board rectifiers produce the high DC voltage for the magnetron. The board also feeds the magnetron filament.
Output is controlled by changing the switching (pulse width), so the magnetron can run at reduced power continuously instead of cycling full on/full off. LG markets its NeoChef range as varying output between about 300 and 1,200 W; European BSH documentation describes continuous reduction down to about 300 W. At the very lowest settings some designs still pulse.
The control board talks to the inverter board and watches for microwave output. On Panasonic units, if no output is detected after Start the control stops and shows an H-code (for example H98; see the microwave error codes file).
Because the board contains filter capacitors and high-voltage parts, it can hold charge after unplugging, just like the capacitor in a transformer unit.
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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): Large stainless refrigerator set flush between kitchen cabinets by Alex Qian, Pexels License
