NN-S651WF, NN-S541WF - Panasonic Home Appliance Service Manual (repair manual). Page 10

Unlike many other appliances, the microwave oven is high-voltage, high

current equipment.  Though it is free from danger in ordinary use, extreme

care should be taken during repair.

   

Do not operate on a 2-wire extension cord.  The microwave oven is

    designed to be used when grounded.  When it is inoperative, make

    sure it is grounded properly before beginning repair work.

CAUTION
Servicemen should remove their watches whenever
working close to or replacing the magnetron.

This High Voltage Inverter Power Supply circuit supplies

very high voltage and very high current for the magnetron

tube.  Though it is free from danger in ordinary use, extreme

care should be taken during repair.  As you can see, it looks

like a TV flyback transformer, however the current is

extremely large and so danger exists because of its high

current and high voltages.

The aluminum heat sink is also energized with high voltage

(HOT), so do not touch when AC input terminal is connected

to the power line because one of the IGBT  switching power

devices (Collector) is directly connected to the Aluminum

heat sink.

The Aluminum heat sink may be HOT from heat energy;

therefore, extreme care should be taken during servicing

and replacing.

Check the High Voltage Inverter Power Supply circuit grounding.

This High Voltage Inverter Power Supply circuit board must have

a proper chassis ground by the grounding bracket to the chassis

ground; otherwise, this H.V. Inverter circuit board will expose

very high voltage and cause extreme DANGER!  Be sure to have

proper grounding by the grounding plate and screws.

Warning about the electric charge in the high voltage capacitors.
For about 30 seconds after the oven is turned off, an electric charge
remains in the high voltage capacitors in the inverter power supply
circuit board.
When replacing or checking parts, remove the power plug from
the outlet and short the Inverter output terminal of the magnetron
filament terminals to the chassis ground with an insulated handle
screwdriver to discharge.  Please make sure to touch chassis
ground side first then short to the output terminals.

There is high-voltage present, with high-current capabilities in the

circuits of the primary, and secondary windings, choke coil and

heat sink of the Inverter.  It is extremely dangerous to work on or

near these circuits with oven energized.

DO NOT measure the voltage in the high voltage circuit including

filament voltage of magnetron.

Never touch any circuit wiring with your hand nor with an

insulated tool during operation.

(A) This is mandatory. Refer to “Measurements and Adjustments”

for these switches.

(B) When replacing the fuse, confirm that it has the appropriate

rating for these models.

(C) When replacing faulty switches, be sure mounting tabs are

not bent, broken or otherwise deficient in their ability to hold

the switches.

Never insert a wire, nail or any other metal object through the

lamp holes on the cavity or any other holes or gaps, because

such objects may work as an antenna and cause microwave

leakage.

When the 18 Amp. fuse if blown due to the operation of

short switch, you must replace Primary latch switch and

short switch. Also replace power relay B (RY1) when the

continuity check reads shorted contacts (1-2).

MAGNETRON

FILAMENT TERMINAL

INSULATED HANDLE

SCREWDRIVER

Touch chassis side first then short to the terminal of the magnetron

filament terminal.

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