Inverter NN-T591WB User manual

MOP01060022C2
Microwave Oven
NN-T591WB
NN-T571SB
NN-T551WB
NN-T551CB
27L
United Kingdom

1
1. Inverter Warning
The inverter board looks like a normal printed circuit board. However, this printed
circuit board supplies the magnetron tube with very high voltage and current.
The inverter PCB:
1. Produces very high voltage and current.
2. Has an Aluminium heat sink which becomes very hot.
3. Has capacitors in the circuitry that hold a high voltage charge even when the oven
is not operating.
Do not
1. Do not touch the high voltage circuitry. When replacing the board take extreme
care to avoid possible electric shock.

2. Do not touch the aluminium heat sink as it is part of the high voltage circuit and
becomes very hot.
3. Do not attempt to repair the inverter PCB as this can be very dangerous. Replace
the high voltage, inverter circuit as a complete unit.
4. Do not adjust or tamper with the pre-set volume on the inverter board. It is very
dangerous to adjust this pre-set without proper test equipment.
5. Do not operate the microwave oven when the inverter grounding plate and fixing
screw is loose. It is very dangerous to operate the inverter circuit board with out a
proper ground connection.
Figure 1
Inverter Power Supply Diagram
Figure 2

Inverter Layout
2. FEATURE CHART
Function NN-T551WB
NN-T551CB NN-T591WBNN- T571SB
Microwave 4 5
Sensor reheat 2
Sensor Cook 14
Turbo reheat 1 1
Weight reheat 4 -
Weight cook 4 -
Weight
combination -
Weight defrost 3 3
Delay/Stand Yes Yes
More / Less - Yes
Kg - lb/oz Yes Yes
Stage cooking 3 3
Clock 12H 12H
Word prompt English English
3. Control Panels

4. Operation And Digital Programmer Test Procedure
4.1. Setting The Clock
1. Plug the power supply cord into the wall outlet
2. Press the clock pad
3. Enter the time of the day

4. Press the clock pad
4.2. Microwave Cooking
1. Place a water load in the oven
2. Press Micro power once to set high power
3. Set time at 10 sec. by pressing
10 sec. pad once
4. Press Micro power pad 3 times to set medium power
5. Set pad for 1 minute by pressing 1 min. pad once
6. Press the start pad

7. When the first stage cooking has elapsed oven automatically switches to second
stage
8. When second stage cooking has elapsed oven bleeps 5 times and shuts off
4.3. Turbo Reheat
1. Place water load in the oven
2. Press the Turbo reheat button once
3. Set time to 1 minute by pressing1 min pad once
4. Press the start pad
4.4. Auto Weight Defrost
1. Select the desired program
2. Press g or lb. and oz.

3. Enter the weight by pressing the Up & Down or more less pads.
4. Press Start
4.5. Delay Stand
1. Set power level and time
2. Press Stand
3. Set standing time
4. Press Start
4.6. Delay Start

1. Press delay
2. Set delay time
3. Set power level and time
4. Press start pad
4.7. Auto Weight Cook Programs NN-T551
1. Select the desired auto weight cook program
2. Press to select grams or pounds and ounces
3. Enter the weight by pressing the up and down pads
4. Press Start
4.8. Auto Sensor Cooking NN-T591 NN-T571
1. Select the desired sensor cook program

2. Press start
4.9. Demonstration Mode
1. Set demonstration mode by pressing the clock pad three times
2. Cancel demonstration mode by pressing the clock pad three times
4.10. Child Lock
1. Set the child lock by pressing the start pad three times
2. Cancel the child lock by pressing the start pad three times
5. Schematic And Wiring Diagram
6. Description Of The Operating Sequence
6.1. Variable power cooking control
The output power is controlled by the inverter power supply, which is controlled by
signals from the digital programmer circuit (DPC). The digital programmer cicruit
operates relay RY1 to supply power to the inverter circuit. The outpower is controlled
by the inverter control signal from the digital programmer circuit.

Variable power cooking
Setting Output On Time Off Time
Turbo 1000W 22 0
High 900W 22 0
Defrost 440W 16 6
Medium 600W 22 0
Low 440W 22 0
Simmer 440W 15 7
Warm 440W 8 14
NOTE 1. The ON/OFF time ratio does not corespond with the percentage of
microwave power since approximately 2 seconds are required to heat the magnetron
filament.
NOTE 2. If the microwave cooking time is longer than 3 minutes, the cooling fan will
operate for 1 minute to cool the oven and its electronic components.
6.2. Auto weight defrost, Auto weight Cook NN-T551
When an auto control feature is selected and the start pad pressed:
1. The digital programmer circuit determines the power level and the cooking time
and indicates the operating state in the display. The table shows the
corresponding cooking times for each category and its respective weight.
2. When the cooking time in the display window has elapsed, the oven turns off
automatically via the control signal from the digital programmer circuit.
Note: After auto cooking if the oven temperature is over the predetermined
temperature the fan motor rotates to cool the oven and its components.
Auto Weight Defrost
Category 1st Touch
Weight Cooking Time
Bread 100g 0 Min 50 Sec
Meat Items 200g 3 Min 0 Sec
Meat Joints 400g 6 Min 20 Sec
Auto Weight Cook
Category 1st Touch
Weight Cooking Time
1.curry 350g 4 Min 22 Sec
2.chinese style 250g 2 Min 55 Sec
3.pasta 300g 3 Min 30 Sec
4.casserole 350g 4 Min 5 Sec
5.fresh vegetables 100g 2 Min 20 Sec
6.fresh fish 100g 1 Min 10 Sec
7.jacket potatoes 200g 4 Min 30 Sec
8.boiled potatoes 200g 4 Min 00 Sec

6.3. One touch Auto sensor cooking NN-T591 NN-T571
Auto sensor cook is a revolutionary way to cook by microwave 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 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 humidity sensor element, senses the
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 the power select and time features. Please consult variable power microwave
cook book for procedures.
Explanation of the auto sensor cooking process
1. The shaded columns in figure 1 indicate when the humidity sensor heater is on.
2. During this 30 second period there is no microwave activity. When calculating the
T2 time by using the formula below, make sure this 30 seconds is subtracted from
the T0 time.
3. T1 time = T0 time - 30 seconds.
4. T2 time. When the steam escapes from the cooking container placed in the oven,
the humidity 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 (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 start pad is tapped. The coefficient K is
programmed into the microprocessor memory and they are listed in the following
tables along with the P1 and P2 powe r.
NOTE: When “More” or “Less” pad is selected, the K factor varies resulting in T2
time to be increased or decreased.
Calculating the T2 time
Example 1: If the T1 time is measured to be 2 minutes and 40 seconds, and the auto
sensor program is selected to sensor reheat. Fresh Fish (Program 3)
T2 = T1 x K
= 2 min 40 sec. X. 0.1
= 16 sec.

Catergory P1
POWER P2 POWER K FACTOR STANDARD
fresh
vegetables HIGH HIGH 0.5
frozen
vegetables HIGH HIGH 0.1
Figure 1
Auto sensor cooking
7. Cautions to Be Observed When Troubleshooting
Unlike many other appliances, the microwave oven is a high voltage, high current
device. Though it is free from danger in ordinary use, extreme care should be taken
during repair.
Caution
Servicemen should remove their watches whenever working close to or replacing
the magnetron.
7.1. Check the grounding

Do not operate on a two wire extension cord. The microwave oven is designed to be
used when grounded. It is imperative, therefore, to ensure the appliance is properly
grounded before beginning repair work.
7.2. Inverter Warnings
DANGER, HIGH VOLTAGE AND HIGH TEMPERATURE (HOT/LINE) OF
THE INVERTER POWER SUPPLY (U)
This 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. As you can see, it looks like a TV flyback transformer,
however, the current is extremely large and is therefore, dangerous due to this high
current and high voltage.
The aluminium heat sink is also energized with high voltage (HOT), so do not touch
when the AC input terminal is connected. The power devices (Collector) is directly
connected to the aluminium heat sink.
The aluminium heat sink may be (HOT) due to heat energy, therefore, extreme care
should be taken during servicing.
Figure 1
HV 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 bracket must be connected to the chassis. If the inverter board is not

grounded it will expose very high voltages and cause extreme DANGER! Be sure
that the inverter circuit is properly grounded via the inverter earth bracket.
Figure 2
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 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.
Figure 3

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 nor with an insulated tool during
operation.
7.3. Part Replacement.
When any part or component is to be replaced, always ensure that the power cord is
removed from the wall outlet.
7.4. 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 short switch, the
primary latch switch and short switch must be replaced. It is also important to
change the power relay 1 (RY1) when the continuity test shows shorted contacts.
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.
7.5. 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.
7.6. 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
DO NOT BECOME EXPOSED TO RADIATION FROM THE MICROWAVE GENERATOR
OR OTHER PARTS CONDUCTING MICROWAVE ENERGY
IMPORTANT NOTICE
The following components have potentials above 250V while is 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 in these areas.

When the appliance is operated with the door hinges or magnetron fixed incorrectly,
the microwave leakage can reach more than 5mW/cm3. After repair or exchange, it is
very important to check if the magnetron and the door hinges are correctly fixed.
7.7. Sharp Edges
Caution
Please use caution when unpacking, installing or moving the unit, as some exposed
edges may be sharp to touch and cause injury if not handled with care.
8. Parts Replacement Procedure
8.1. Magnetron
1. Discharge the high voltage capacitors on the inverter circuit.
2. Remove the screw holding the air guide.
3. Remove the two screws holding the tie bar.
4. Remove the oven lamp and lead wire harness cables form the air guide A.
5. Remove the air guide A.
6. Disconnect the two high voltage leads from the magnetron.
7. Remove the four screws holding the magnetron.
NOTE: After replacing the magnetron, tighten the mounting screws making sure that
there is no gap between the waveguide and the magnetron to prevent microwave
leakage.
Caution
When replacing the magnetron, ensure that the antenna gasket is in place.
Note
The magnetron used for this model is unique for the inverter power supply system.
Make sure to use the one as listed in the parts list.
Figure 1