Cautions To Be Observed When Troubleshooting; Check The Grounding; Inverter Warnings - Panasonic NN-T559WB Service Manual

5.

CAUTIONS TO BE OBSERVED WHEN TROUBLESHOOTING

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

5.1 Check the grounding

Do not operate on a 2-wire extension cord. The microwave oven
is designed to be used when grounded. It is imperative,
therefore, to make sure it is grounded properly before beginning
repair work.

5.2 Inverter Warnings

DANGER OF HIGH VOLTAGE AND HIGH TEMPERATURE
(HOT/LINE) OF THE INVERTER POWER SUPPLY (U)
This High Voltage Inverter Power Supply circuit handles 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 by its high current and high voltages.
The aluminium heat sink is also energized with high voltage
(HOT), so do not touch when AC input terminal is connected to
the power devices (Collector) is directly connected to the
Aluminium heat sink.
The Aluminium heat sink may be HOT by heat energy;
therefore, extreme care should be taken during servicing and
replacing.
DANGER OF HIGH VOLTAGE AND HIGH
TEMPERATURE (HOT/LIVE) OF HEAT SINK
HEAT SINK
CHOKE COIL
SAND BAR
RESISTOR
CUSTOM I.C.
PHOTO
COUPLER
CN 701
CURRENT
HIGH VOLTAGE REMAINS IN
TRANSFORMER
HIGH VOLTAGE CAPACITORS
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.
CAUTION
NEW H.V.
HIGH VOLTAGE
TRANSFORMER
HIGH VOLTAGE
DIODE
SECONDARY
WINDINGS
CN 703
WARNING OF DISCHARGING HIGH VOLTAGE
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.
Touch chassis side first then short to the
te rm inal of the m agnetron filam ent te rm inal
MAGNETRON FILAMENT
TERMINAL
INSULATED HANDLE
FILM
CAPACITORS
SCREWDRIVER
PRIMARY
WINDINGS
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.
10
H.V. INVERTER(U)
BE SURE TO HAVE PROPER
GROUNDING
GROUNDING PLATE
CAPACITORS
WARNING
WARNING