Panasonic NNS252BF - MICROWAVE OVEN/OTR Service Manual Download

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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.

CAUTION

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

8.1. Check the grounding

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.

8.2. Inverter warnings NEW H.V.

DANGER OF HIGH VOLTAGE AND HIGH

TEMPERATURE (HOT/LIVE) OF THE INVERTER

POWER SUPPLY (U)

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.

WARNING OF INVERTER POWER SUPPLY (U)

GROUNDING

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 OF DISCHARGING HIGH VOLTAGE

CAPACITORS

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.

WARNING

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.

WARNING

Never touch any circuit wiring with your hand nor with an insulated
tool during operation.

8.3. When parts must be replaced,

remove the power plug from
the outlet.

8.4. When the 18 Amp fuse is

blown due to the operation of
short switch:

WARNING

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).

1. This

mandatory.

Refer

"Measurements

and

Adjustments" for these switches.

2. When replacing the fuse, confirm that it has the appropriate

rating for these models.

3. When replacing faulty switches, be sure mounting tabs are

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

8 CAUTIONS TO BE OBSERVED WHEN

TROUBLESHOOTING