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NN-G55 AR
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.
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 inoperative,
therefore, to make sure it is grounded properly before beginning
repair work.
2. Inverter Warnings
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 NEVER TOUCH ANY CIRCUIT WIRING WITH
YOUR HAND NOR WITH AN INSULATED TOOL DURING
OPERATION.
3. When parts must be replaced, remove the power
plug from the outlet.
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).
(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.
5. Avoid inserting nails, wire, etc. through any holes in
the unit during operation.
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.
6. Confirm after repair
(A) After repair or replacement of parts, make sure that the
screws of the oven, etc. are neither loose nor missing.
Microwaves might leak if screws are not properly
tightened.
(B) Make sure that all electrical connections are tight before
inserting the plug into the wall outlet.
(C) Check for microwave energy leakage. (Refer to proce-
dure for measuring microwave energy leakage.)
IMPORTANT NOTICE
1. The following components have potentials above 250V while
the appliance is operating..
• Magnetron
• High voltage transformer (Located on Inverter (U))
• High voltage diodes (Located on Inverter (U))
• High voltage capacitors (Located on Inverter (U))
Pay special attention on these portions.
2. When the appliance is operated with the door hinges or
magnetron fixed incorrectly, the microwave leakage can reach
more than 5mW/cm2. After repair or exchange, it is very
important
to check if magnetron and the door hinges are correctly fixed.
