Precautions To Be Observed When Troubleshooting - Whirlpool MH9180XL Service Manual

PRECAUTIONS TO BE OBSERVED WHEN TROUBLESHOOTING

The microwave oven is a high voltage, high
current appliance. It is free from danger during
ordinary use, but extreme care should be taken
during repair.
CAUTION
Service technicians should remove their
watches whenever working close to or re-
placing the magnetron.
DANGER
HIGH VOLTAGE AND HIGH TEMPERA-
TURE (HOT/LIVE) OF THE INVERTER
POWER SUPPLY
The high voltage inverter power supply cir-
cuit 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. 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 it
when the AC input terminal is connected to
the power line. One of the IGBT switching
power devices (collector) is directly con-
nected 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
INVERTER POWER
SUPPLY GROUNDING
Check the high voltage inverter power sup-
ply circuit grounding. This high voltage in-
verter 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 DAN-
GER. Be sure to have proper grounding by
the grounding plate and screws.
DISCHARGING 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. Use a screw-
driver with an insulated handle, and short the
inverter output of the magnetron filament
terminals to discharge it. Be sure to touch the
chassis ground side first, and then touch the
output terminals.
There is high voltage present, with high
current capabilities in the circuits of the pri-
mary and secondary windings, the choke
coil, and the heat sink of the inverter. It is
extremely dangerous to work on or near
these circuits with the microwave oven ener-
gized. DO NOT measure the voltage in the
high voltage circuit, including the filament
voltage of the magnetron.
Never touch any circuit wiring with your
hand, or with an insulated tool during opera-
tion.
Never insert a wire, nail, or any other metal
object through the lamp holes on the cavity,
or any other holes or gaps. Doing so may act
as an antenna, and cause microwave leak-
age.
Before touching any oven components or
wiring, always unplug the oven from its
power source, and discharge the capaci-
tors in the high voltage inverter.
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WARNING
WARNING
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