Panasonic Nn St452w User Manual

							© Panasonic Appliances Microwave Oven
(Shanghai) Co., Ltd. 2012.
NN-SD452W
NN-ST462M
NN-ST452W
BPQ (U.K.)
EPG (Continental Europe)
Microwave Oven
ORDER NO.PAPMOSH1201015CE 
						

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NN-SD452W / NN-ST462M / NN-ST452W 
						

							3
NN-SD452W / NN-ST462M / NN-ST452W 
						

							 1 SCHEMATIC DIAGRAM 5
 2 DESCRIPTION OF OPERATING SEQUENCE 
6
 2.1. Variable power cooking control 
6
 2.2. Inverter power supply circuit 
6
 2.3. Turbo defrost, Auto cook 
6
 2.4. Sensor cooking 
6
 2.5. Steam sensor and digital programmer circuit 
7
 3 CAUTIONS TO BE OBSERVED WHEN TROUBLESHOOTING 
8
 3.1. Check the grounding 
8
 3.2. Inverter warnings 
8
 3.3. Part replacement. 
9
 3.4. When the 10A fuse is blown due to the malfunction of the
short switch: 
9
 3.5. Avoid inserting nails, wire etc. through any holes in the
unit during operation. 
9
 3.6. Verification after repair 
9
 3.7. Sharp edges 
9
 4 DISASSEMBLY AND PARTS REPLACEMENT PROCEDURE 
10
 4.1. Magnetron 
10
 4.2. Digital programmer circuit (D.P.C) 
10
 4.3. Low voltage transformer and/or power relays (RY1, RY2)
 
11
 4.4. Fan motor 
11
 4.5. Door assembly 
11
 4.6. Turntable motor 
13
 4.7. Steam sensor 
13
 4.8. Inverter power supply 
14
 5 COMPONENT TEST PROCEDURE 
15 5.1. Primary, Secondary Latch Switch interlocks & Power
Relay RY1 
15
 5.2. Short Switch 
15
 5.3. Magnetron 
15
 5.4. key board membrane (Membrane switch assembly) 
15
 5.5. Inverter power supply (U) 
16
 5.6. Temperature thermistor 
16
 6 MEASUREMENTS AND ADJUSTMENTS 
17
 6.1. Adjustment of primary latch switch, secondary latch switch
and short switch. 
17
 6.2. Measurement of microwave output 
17
 7 TROUBLESHOOTING GUIDE 
18
 7.1. (Troubleshooting) Oven stops operation during cooking 
18
 7.2. (Troubleshooting) Other problems 
19
 7.3. Troubleshooting of inverter circuit (U) and magnetron 
20
 7.4. Simple way of H.V. Inverter/magnetron troubleshooting 
21
 7.5. How to check the semiconductors using an OHM meter 
21
 7.6. H.V. INVERTER MAIN PARTS LIST (Z606YBA00QP) 
22
 8 EXPLODED VIEW AND PARTS LIST 
23
 8.1. EXPLODED VIEW  
23
 8.2. PARTS LIST 
24
 8.3. ESCUTCHEON BASE ASSEMBLY 
25
 8.4. DOOR ASSEMBLY 
27
 8.5. WIRIN G MATERIALS 
28
 8.6. PACKING AND ACCESSORIES 
29
 9 DIGITAL PROGRAMMER CIRCUIT 
30
 9.1. SCHEMATIC DIAGRAM (NN-SD452W ) 
30
 9.2. SCHEMATIC DIAGRAM (NN-ST462M, ST452W)  
32
CONTENTS
 Page  Page
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NN-SD452W / NN-ST462M / NN-ST452W 
						

							1 SCHEMATIC DIAGRAM
5
NN-SD452W / NN-ST462M / NN-ST452W 
						

							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 stay 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 CookingPOWE R SETTINGOUTPUT
POWE R(%)
APPROX.MANUAL MICROWAV E
DUTY
BPQEPGON(SEC)OFF(SEC)
TURBO1000W100%220
HIGH—90%220
DEFROST270W25%157
MEDIUM600W60%220
LOW440W45%220
SIMMER300W30%220
WARM100W10%814
2.2. Inverter power supply circuit
The Inverter Power Supply circuit powered from the line
voltage, 230V 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 230V 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. Turbo defrost, Auto cook
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.
 2. When cooking time in the display window has elapsed, the
oven turns off automatically by a control signal from the
digital programmer circuit.
2.4. Sensor cooking
Auto sensor cooking without setting a power level or selecting
a time. All that is necessary is to select an Auto Sensor
Program before starting to cook.
Understanding Auto Sensor Cooking
As the food cooks, a certain amount of steam is produced.
If the food is covered, this steam builds up and eventually
escapes from the container. In Auto Sensor Cooking, a
carefully designed instrument, called the steam sensor
element, senses this escape of steam. Then, based upon
the Auto Sensor Program selected, the unit will
automatically determine the correct power level and the
proper length of time it will take to cook the food.
NOTE:
Auto Sensor Cooking is successful with the foods and
recipes found in the Auto Sensor Cooking Guide.
Because of the vast differences in food composition,
items not mentioned in the Cooking Guide should be
prepared in the microwave oven using power select
and time features. Please consult Variable Power
Microwave Cookbook for procedures.
2 DESCRIPTION OF OPERATING SEQUENCE
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NN-SD452W / NN-ST462M / NN-ST452W 
						

							Explanation of the Auto Sensor Cooking process
 1. During the first 10 second period there is no microwave
activity. When calculating the T2 time by using the
formula below make sure this 10 seconds is subtracted
from the T1 time. In other words, T1 time starts at the
end of the 10 second period.
 2. T1 timeThe total amount of time it takes the microwave
oven to switch to T2 time after the 10second period.
 3. T2 timeWhen the steam escapes from the cooking
container placed in the oven, the steam sensor detects
it and the microprocessor calculates the balance of
cooking time. This T2 time is then shown in the display
and begins counting down.
Balance of cooking time (T2 time)
The balance of cooking time which is called T2 time,
can be calculated by the following formula.
T2 time (in sec.) = T1 time X K factor
NOTE:
Remember, the T1 time starts after the 10 second
period. The coefficient K is programmed into the
microprocessor memory and they are listed in the
following tables along with the P1 and P2 powers.
NOTE:
When More or Less pad is selected, the K factor
varies resulting in T2 time to be increased or decreased.
Example of calculating the T2 time
Example 1: If the T1 time is measured to be 2 minutes and
40 seconds after the 10 second period.
T2 = T1 × K
= 2 min. and 40 sec. × 0.1
= 160sec. × 0.1
= 16 sec.
CategoryP1
PowerP2
PowerK Factor
Standard
BPQFresh
Vegetable900W900W0.5
EPG1000W1000W0.5
2.5. Steam sensor and digital
programmer circuit
In order to determine if the steam sensor function of the digital
programmer circuit is working, do the following test.
 1. Place a water load (150 cc) in the oven.
 2. Tap Sensor Reheat pad.
 3. Tap Start pad.
 4. Steam Sensor detects steam about 1.5 to 4 minutes after
the Start pad is tapped.
 5. T1 time cooking automatically switches to remaining time
for cooking (T2).
 6. The remaining cooking time (T2) appears in display
window. If the following cooking time appears, Steam
Sensor function is normal.
T1 TIMET2 TIME (Remainingcooking time)
50 Sec. ~ 12 Min.0 Sec. ~ 10 Min.42 Sec.
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NN-SD452W / NN-ST462M / NN-ST452W 
						

							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 & rings 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
WARNING HIGH VOLTAGE AND HIGHTEMPERATURE
(HOT/LIVE) OF THE INVERTERPOWER SUPPLY (U)
The High Voltage Inverter Power Supply generates 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.
H.V. Inverter warning
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 plate 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
grounding plate.
Grounding of the inverter circuit board
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 of 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 contact the chassis ground side first and then short to the
output terminal.
3 CAUTIONS TO BE OBSERVED WHEN
TROUBLESHOOTING
8
NN-SD452W / NN-ST462M / NN-ST452W 
						

							Discharging the high voltage capacitors
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.
3.3. Part replacement.
When troubleshooting any part or component is to be replaced,
always ensure that the power cord is unplugged from the wall
outlet.
3.4. When the 10A fuse is blown
due to the malfunction of the
short switch:
WARNING
When the 10A 250V fuse is blown due to the malfunction of
the short switch, replace all of the components (primary
latch switch, short switch and power relay RY1).
 1. This is mandatory. Refer to “measurements and
adjustments” 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. Verification after repair
 1. After repair or replacement of parts, make sure that the
screws of the oven, etc. are neither loosen or missing.
Microwave energy 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.
CAUTION OF MICROWAVE RADIATION LEAKAGE
USE CAUTION NOT TO BECOME EXPOSED TO
RADIATION FROM THE MICROWAV E MAGNETRON OR
OTHER PARTS CONDUCTING MICROWAV E ENERGY.
IMPORTANT NOTICE
 1. 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.
 2. When the appliance is operated with the door hinges or
magnetron installed incorrectly, the microwave leakage
can exceed more than 5mW/cm
2. 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 disassembling or reassembling
internal parts. Some exposed edges may be sharp to the
touch and can cause injury if not handled with care.
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NN-SD452W / NN-ST462M / NN-ST452W 
						

							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 air guide A on cavity top plate.
 4. Remove 1 screws holding thermistor on the magnetron.
 5. Remove 1 screw holding air guide A on the wave guide,
then remove the air guide A.
 6. Remove 4 screws holding the magnetron.
NOTE:
After replacement of the magnetron, tighten mounting
screws properly, 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.
4.2. Digital programmer circuit
(D.P.C)
CAUTION:
Be sure to ground any static electric charge built up in
your body before handling the DPC.
 1. Disconnect connector CN701 on H.V. Inverter board.
 2. Remove 1 screw holding escutcheon base and slide the
escutcheon base upward slightly.
 3. Remove all screws holding D.P.C. board on escutcheon
base.
 4. Separate D.P.C board from tabs on the escutcheon base
and remove D.P.C board.
To replace membrane key board
 5. Use tools such as kinfe etc. to lift the edge of escutcheon
sheet and peel off escutcheon sheet & key board
membrane 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 the new key board membrane, make
sure that the surface of escutcheon base is clean to
prevent a malfunction or shorted contacts.
4 DISASSEMBLY AND PARTS REPLACEMENT
PROCEDURE
10
NN-SD452W / NN-ST462M / NN-ST452W