Panasonic NN-GD376S User manual

© 2006 Panasonic Home Appliances Microwave
Oven (Shanghai) Co., Ltd. All rights reserved.
Unauthorized copying and distribution is a violation
of law.
NN-GD376S
NN-GD366M
NN-GD356W
BPQ (U.K.)
EPG (France, Italy, Finland, Spain, Portugal, Greece,
Poland, Holland)
WPG (Switzerland)
Microwave Oven
ORDER NO.PHAMOS0605031C2

2
NN-GD376S / NN-GD366M / NN-GD356W

3
NN-GD376S / NN-GD366M / NN-GD356W

1 SCHEMATIC DIAGRAM 5
2 DESCRIPTION OF OPERATING SEQUENCE 6
2.1. Variable power cooking control 6
2.2. Inverter power supply circuit NEW H.V. 6
2.3. Inverter defrost, Auto menu & Auto reheat 6
3 CAUTIONS TO BE OBSERVED WHEN TROUBLESHOOTING
7
3.1. Check the grounding 7
3.2. Inverter warnings 7
3.3. Part replacement. 8
3.4. When the 10A fuse is blown due to the operation of the
short switch: 8
3.5. Avoid inserting nails, wire etc. through any holes in the
unit during operation. 8
3.6. Confirm after repair 8
3.7. Sharp edges 8
4 DISASSEMBLY AND PARTS REPLACEMENT PROCEDURE 9
4.1. Magnetron 9
4.2. Digital programmer circuit (D.P.C) and membrane key
board. 9
4.3. Low voltage transformer and/or power relays (RY1, RY2)
10
4.4. Fan motor 10
4.5. Door assembly 11
4.6. Turntable motor 11
4.7. Quartz heater 12
4.8. H.V. Inverter Power Supply 12
5 COMPONENT TEST PROCEDURE 13
5.1. Primary latch switch (door switch and power relay B)
interlocks. 13
5.2. Short switch & monitor 13
5.3. Magnetron 13
5.4. Membrane key board (Membrane switch assembly) 13
5.5. Inverter power supply (U) 14
5.6. Temperature thermistor 14
6 MEASUREMENTS AND ADJUSTMENTS 15
6.1. Adjustment of Primary latch switch, Secondary latch
switch and Short switch. 15
6.2. Measurement of microwave output 15
7 TROUBLESHOOTING GUIDE 16
7.1. (Trouble) Oven stops operation during cooking 16
7.2. Trouble related to Digital Programmer Circuit 18
7.3. Troubleshooting of inverter circuit (U) and magnetron
NEW H.V. 19
7.4. Simple way of H.V. Inverter/magnetron troubleshooting
20
7.5. How to check the semiconductors using an OHM meter
20
8 EXPLODED VIEW AND PARTS LIST 21
8.1. EXPLODED VIEW 21
8.2. PARTS LIST 22
8.3. DOOR ASSEMBLY 23
8.4. WIRING MATERIALS 23
8.5. ESCUTCHEON BASE ASSEMBLY 24
8.6. PACKING AND ACCESSORIES 26
8.7. H.V. INVERTER MAIN PARTS LIST 26
9 DIGITAL PROGRAMMER CIRCUIT 27
9.1. SCHEMATIC DIAGRAM (NN-GD376S) 27
9.2. SCHEMATIC DIAGRAM (NN-GD366M, GD356W) 29
9.3. PARTS LIST 31
CONTENTS
Page Page
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NN-GD376S / NN-GD366M / NN-GD356W

1 SCHEMATIC DIAGRAM
5
NN-GD376S / NN-GD366M / NN-GD356W

2.1. Variable power cooking
control
High Voltage Inverter Power Supply (U) controls output power
by the signal from Digital Programmer Circuit (DPC). Power
relay always stays ON, but PWM (pulse width modulation)
signal controls microwave output power.
NOTE:
The ON/OFF time ratio does not correspond with the
percentage of microwave power since approximately 2
seconds are required for heating of magnetron
filament.
Variable Power Cooking
POWER SETTING OUTPUT
POWER(%)
APPROX.
MANUAL MICROWAVE
DUTY
ON(SEC) OFF(SEC)
HIGH 100% 22 0
DEFROST 30% 17 5
MEDIUM 70% 22 0
MEDIUM-LOW 50% 22 0
SIMMER 30% 17 5
WARM 10% 9 13
2.2. Inverter power supply circuit
NEW H.V.
The Inverter Power Supply circuit powered from the line
voltage, 230-240V 50Hz AC input supplies 4,000V DC to the
magnetron tube, and functions in place of the H.V. transformer,
the H.V. capacitor and H.V. diode.
1. The AC input voltage 230-240V 50Hz is rectified to DC
voltage immediately.
2. DC voltage will be supplied to the switching devices called
IGBT. These devices are switched ON-OFF by the 20 to 40
kHz PWM (pulse width modulation) signal from the
microcomputer in the DPC.
3. This drives the High voltage transformer to increase voltage
up to 2,000V AC.
4. Then the half-wave doubler voltage rectifier circuit,
consisting of the H.V. diodes and capacitors, generates the
necessary 4,000V DC needed for the magnetron.
5. Output power of the magnetron tube is always monitored by
the signal output from the current transformer built into the
inverter circuit.
6. This signal is fed back to the microcomputer in the DPC to
determine operating conditions and output necessary to
control PWM signal to the Inverter Power Supply for control
of the output power.
2.3. Inverter defrost, Auto menu &
Auto reheat
When the Auto Control feature is selected and the Start pad is
tapped:
1. The digital programer circuit determines the power level and
cooking time to complete cooking and indicates the
operating state in the display window. Table shows the
corresponding cooking times for respective serving by
categories.
Weight Deforst (Meat Items)
For BPQ models:
SELECTED WEIGHT COOKING TIME
1200 g 25 min.00 sec.
For EPG/WPG models:
SELECTED WEIGHT COOKING TIME
1200 g 21 min.30 sec.
Weight Cook(Fresh Vegetables)
For BPQ models:
SELECTED WEIGHT COOKING TIME
200 g 3 min.40 sec.
For EPG/WPG models:
SELECTED WEIGHT COOKING TIME
200 g 5 min.40 sec.
2. When cooking time in the display window has elapsed, the
oven turns off automatically by a control signal from the
digital programmer circuit.
2 DESCRIPTION OF OPERATING SEQUENCE
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NN-GD376S / NN-GD366M / NN-GD356W

Unlike many other appliances, the microwave oven is a high
voltage, high current device. It is free from danger in ordinary
use, though extreme care should be taken during repair.
Caution
Servicemen should remove their watches whenever
working close to or replacing the magnetron.
3.1. Check the grounding
Do not operate on a two wire extension cord. The microwave
oven is designed to be grounded when used. It is imperative,
therefore, to ensure the appliance is properly grounded before
beginning repair work.
3.2. Inverter warnings
DANGER, HIGH VOLTAGE AND HIGH TEMPERATURE
(HOT/LINE) OF THE INVERTER POWER SUPPLY (U)
The high voltage inverter power supply handles very high
voltage and current for the magnetron tube. Though it is
free from danger in ordinary use, extreme care should be
taken during repair.
The aluminum heat sink is also energized with high voltage
(HOT), do not touch when the AC input terminals are
energized. The power device Collector is directly connected
to the aluminum heat sink.
The aluminum heat sink may be HOT due to heat energy,
therefore, extreme care should be taken during servicing.
WARNING FOR INVERTER POWER SUPPLY (U)
GROUNDING
Check the high voltage inverter power supply circuit
grounding. The high voltage inverter power supply circuit
board must have a proper chassis ground. The inverter
grounding bracket must be connected to the chassis. If the
inverter board is not grounded it will expose the user to very
high voltages and cause extreme DANGER! Be sure that
the inverter circuit is properly grounded via the inverter
earth bracket.
WARNING! DISCHARGE THE HIGH VOLATGE
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 be sure
to touch the chassis ground side first and 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 the oven energized.
DO NOT measure the voltage in the high voltage circuit
including the filament voltage of the magnetron.
WARNING
Never touch any circuit wiring with your hand or with an
insulated tool during operation.
3 CAUTIONS TO BE OBSERVED WHEN
TROUBLESHOOTING
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NN-GD376S / NN-GD366M / NN-GD356W

3.3. Part replacement.
When any part or component is to be replaced, always ensure
that the power cord is removed from the wall outlet.
3.4. When the 10A fuse is blown
due to the operation of the
short switch:
WARNING
When the 10A 250V fuse is blown due to the operation of
the interlock monitor switch, replace all of the components
(primary latch switch, secondary latch switch, short switch
and power relay B (RY1)).
1. This is mandatory. Refer to “adjustments and
measurements” for the location of these switches.
2. When replacing the fuse, confirm that it has the
appropriate rating for these models.
3. When replacing faulty switches, be sure the mounting
tabs are not bent, broken or deficient in their ability to
hold the switches.
3.5. 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 holes or gaps, because such
objects may work as an antenna and cause microwave
leakage.
3.6. Confirm after repair
1. 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.
2. Make sure that all electrical connections are tight before
inserting the plug into the wall outlet.
3. Check for microwave energy leakage. (Refer to procedure
for measuring microwave energy leakage).
CAUTION MICROWAVE RADIATION
USE CAUTION NOT TO BECOME EXPOSED TO
RADIATION FROM THE MICROWAVE MAGNETRON OR
OTHER PARTS CONDUCTING MICROWAVE ENERGY
IMPORTANT NOTICE
The following components have potentials above 2000V
while the appliance is operated.
•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 to these areas.
When the appliance is operated with the door hinges or
magnetron installed incorrectly, the microwave leakage can
exceed more than 5mW/cm2. After repair or exchange, it is
very important to check if the magnetron and the door
hinges are correctly installed.
3.7. Sharp edges
Caution
Please use caution when unpacking, installing or moving
the unit, as some exposed edges may be sharp to the touch
and cause injury if not handled with care.
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NN-GD376S / NN-GD366M / NN-GD356W

4.1. Magnetron
1. Discharge the high voltage capacitor.
2. Remove 1 screw holding air guide A on the magnetron.
3. Remove 1 screw holding reinforce bracket on the
magnetron.
4. Remove 1 screw holding thermistor on the magnetron.
5. Disconnect 2 high voltage lead wires from magnetron
filament terminals.
6. Remove 4 screws holding magnetron.
NOTE:
After replacement of the magnetron, tighten mounting
screws properly in an x pattern, making sure there is no
gap between the waveguide and the magnetron to
prevent microwave leakage.
CAUTION
When replacing the magnetron, be sure the antenna gasket is in
place.
CAUTION
When connecting 2 filament lead wires to the magnetron terminals,
be sure to connect the lead wires in the correct position. The lead wire
of high volatge transformer should be connected to “F terminal” and
the lead wire from high voltage capacitor should be connected to “FA
terminal”.
4.2. Digital programmer circuit
(D.P.C) and membrane key
board.
NOTE:
Be sure to ground any static electric charge built up on
your body before handling the DPC.
1. Disconnect all connectors from D.P.C. board.
2. Disconnect connector CN701 from H.V. inverter.
3. Unplug flat cabel from CN6 on D.P.C. board (DU) by
carefully pulling outward.
4. Remove 2 screws holding small D.P.C. board (DU) on
backstop.
5. Remove 4 screws holding backstop on big D.P.C. board
(DU).
4 DISASSEMBLY AND PARTS REPLACEMENT
PROCEDURE
9
NN-GD376S / NN-GD366M / NN-GD356W

To replace pop-up dial
Remove pop-up dial from small D.P.C. board (DU) by
pulling it straight out.
6. Release 2 locking tabs on escutcheon base to remove big
D.P.C. board (DU)
7. Remove 4 screws holding D.P.C. board (AU) on
escutcheon base.
8. Release 6 locking tabs on escutcheon base to remove
D.P.C. board (AU).
To replace membrane key board
Use such as knife etc. tools poke from the edge of
escutcheon sheet and peel off escutcheon sheet and
membrane key board completely from escutcheon base.
NOTE:
1. The membrane key board is attached to the
escutcheon base with double faced adhesive tape.
Therefore, applying hot air such as using a hair dryer is
recommended for smoother removal.
2. When installing new membrane key board, make
sure that the surface of escutcheon base is cleaned
sufficiently so that any problems (shorted contacts or
uneven surface) can be avoided.
3. Alignment position of membrane key board is as
follows;
Membrane key board: Right and upper edges
Escutcheon sheet: Right and upper edges
4.3. Low voltage transformer
and/or power relays (RY1,
RY2)
NOTE:
Be sure to ground any static electric charge built up on
your body before handling the DPC.
1. Using solder wick or a desoldering tool and 30W soldering
iron carefully remove all solder from the terminal pins of the
low voltage transformer and/or power relays.
NOTE:
Do not use a soldering iron or desoldering tool of
more than 30 watts on D.P.C. contacts.
2. With all the terminal pins cleaned and separated from
D.P.C. contacts, remove the defective transformer/power
relays, Replace components making sure all terminal pins
are inserted completely resolder all terminal contacts
carefully.
4.4. Fan motor
1. Disconnect 2 lead wires from fan motor terminals.
2. Remove 3 screws holding orifice assy and detach the orifice
assy from oven assy.
3. Remove fan blade from the motor shart by pulling it stralght
out.
4. Remove 2 screws holding fan motor on orifice assy and
detach the fan motor from orifice assy.
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NN-GD376S / NN-GD366M / NN-GD356W