Panasonic NN-A750WB User manual

Order Number MOP00080014C2
Microwave Oven
NN-A750WB
NN-A720MB
NN-A770SB
27L
WHITE SILVER STAINLESS
United Kingdom
Specification
Power Source 240VAC Single phase, 50Hz
Power Requirements Micro 1260W Grill 1360W Conv 1470w Combi
2770W
Output (IEC705-88) Micro 1000W Grill 1300W Conv 1400W
Microwave Frequency 2450MHz
Timer
99 Minutes 99 Seconds
Oven Cavity Size 27L
Outside Dimensions 510mm(W) x 477mm(D) x 314mm(H)
Inside Dimensions 359mm(W) x 352mm(D) x 217mm(H)
Weight 15Kg
© 1995 Matsushita Electric Industrial Co., Ltd. All
rights reserved. Unauthorized copying and distribu-
tion is a violation of law.

2
1 Inverter Warning
The inverter board looks like a regular PCB, however, this PCB
drives the magnetron tube using very high voltages and cur-
rent.
It has
1. Very high voltage and high current
2. An Aluminium heat sink that becomes very hot
3. The capacitors on the inverter circuit will contain a high
voltage charge even when the oven is not operating.
Do not
1. Do not touch the circuitry as it contains very high volt-
ages. When replacing the board please take extreme
care to avoid possible electric shock. High voltages may
remain in the circuit.
2. Do not touch the aluminium heat sink as it will become
very hot. It also contains high voltages.
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. Return the old unit fully repacked in
the original shipping box and completed paper work.
4. Do not adjust or tamper with the preset volume on the
inverter board. It is very dangerous to adjust this preset
without proper test equipment.
5. Do not test the oven while the inverter grounding strip or
screws are loose. It is very dangerous to operate the
inverter circuit board with out a proper ground connection.
Inverter Power Supply Diagram
Figure 1
Inverter Layout
Figure 2
2 Feature Chart
Function
Microwave 6
Grill 3
Convection 17
Combination YES
Weight Defrost 3
Weight Combination 8
Weight Reheat 4
Weight Cook 2
Stage Cooking 3 Stage
Delay / Stand Yes
Kg lb./oz. Yes
Clock 12 Hour
Word Prompt English

3
3 Control Panels

4
4 Operation And Digital Programmer Circuit Test Procedure
4.1. Setting The Clock
4.2. Microwave Cooking
4.3. Auto Weight Defrost
4.4. Delay Stand
4.5. Delay Start
4.6. Grill Operation
4.7. Convection Operation
(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
(1) Place a water load in the
oven
(2) Press Micro power once
to set high power
(3) Set time at 5 sec. by
pressing
1 sec. pad 5 times
(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
(1) Select the desired pro-
gram
(2) Press g or lb. and oz.
(3) Enter the weight by
pressing the Up & Down
Pads.
(4) Press Start
(1) Set power level and time
(2) Press Stand
(3) Set standing time
(4) Press Start
(1) Press delay
(2) Set delay time
(3) Set power level and time
(4) Press start pad
(1) Select grill power press
once for grill 1
(2) Set cooking time
(3) Press start
(1) Press convection pad to
select oven temperature
(2) Press start to preheat
(3) Press time pads to enter
cooking time
(4) Press start pad

5
4.8. Turbo Bake Operation
4.9. Combination Cooking (Convec-
tion And Microwave)
4.10. Combination Cooking (Grill
And Microwave)
4.11. Combination Cooking (Turbo
Bake And Microwave)
(1) Press turbo bake pad to
select oven temperature
(2) Press grill pad to select
grill power
(3) Press start to preheat
(4) Press time pads to enter
cooking time
(5) Press start
(1) Press combination pad
(2) Press convection pad to
select oven temperature
(3) Select micro power
(4) Press start if preheating
(5) Set cooking time
(6) Press start pad
(1) Press combination pad
(2) Press grill pad to select
oven temperature
(3) Select micro power
(4) Set cooking time
(5) Press start pad
(1) Press combination pad
(2) Press convection pad to
select oven temperature
(3) Select micro power
(4) Press start if preheating
(5) Set cooking time
(6) Press start pad

6
4.12. Auto Weight Cook Programs
(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

7
5 Schematic Diagram
6 Wiring Diagram

8
7 Description of Operating instruction
7.1. Variable power cooking control
The HIGH VOLTAGE INVERTER POWER SUPPLY controls
the output power by a signal from the digital Programmer circuit
DPC. The power relay (RY1) turns on to supply power to the
inverter circuit. The level of output power is controlled by the
drive signal level form the inverter circuit.
NOTE1: The ON/OFF time ratio does not correspond with
the percentage of microwave power since approximately 2
seconds are required for heating the magnetron filament.
NOTE: 2 If microwave cooking is over 8 minutes on HIGH
power, the fan motor rotates for 1 minute after cooking to
cool the oven and electrical components.
Duty cycles for microwave cooking
7.2. Grill Cooking
The digital programmer circuit controls the grill power by oper-
ating the power relay RY4 in the sequence shown in the table
below
Duty cycles for Grill Cooking
7.3. Auto weight defrost, Auto
weight Cook
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
Auto weight Cook
Output Duty ON/OFF
ON time OFF time
High 1000W 22” 0”
Defrost 440W 16” 6”
Medium 600W 22” 0”
Low 440W 22” 0”
Simmer 440W 15” 7”
Warm 440W 8” 14”
Duty ON/OFF
ON Time OFF Time
Grill 1 33” 0”
Grill 2 24” 9”
Grill 3 18” 15”
Category 1st Touch Weight Cooking Time
Bread 100g 45s
Meat Items 200g 2m 10s
Meat Joints 400g 6m 20s
Category 1st Touch Weight Cooking Time
1.Curry 300g 3m 30s
2.Chinese Style 200g 2m 10s
3.Pasta 250g 2m 55s
4.Casserole 300g 3m 15s
5.Fresh Fish 100g 1m 30s
6.Fresh Vegetables 100g 2m 20s
7.Chilled Crispy Top 300g 8m
8.Frozen Crispy Top 300g 12m
9.Jacket Potatoes 200g 9m
10.Frozen Potato Products 200g 8m
11.Whole Chicken 1000g 19m 20s
12.Lamb/Beef 500g 14m 40s
13.Chilled Pizza 200g 6m 40s
14.Frozen Pizza 200g 9m

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7.4. Convection Cooking
1. The digital programmer circuit operates the power relays
RY3,RY5 and RY6 in the sequence as shown in the fig-
ure below.
2. When the oven reaches a predetermined temperature the
digital programmer circuit stops supplying power to relay
RY5, resulting in the convection heater turning off.
3. When the temperature drops below the predetermined
temperature, the digital programmer circuit supplies
power to power relay RY5 resulting in the convection
heater turning on.
Note: After the convection process, if the oven tempera-
ture is higher than the predetermined temperature, the
fan motor rotates to cool the electronic components and
the oven.
Convection Cooking Duty Cycles
Figure1

10
7.5. Combination Cooking
Combination cooking is achieved by operating the microwave
and heater modes together during one cooking cycle. There
are three combination modes.
1. Combination (convection and microwave)
2. Combination (grill and microwave)
3. Combination (grill, convection and microwave)
The digital programmer circuit operators the power relays as
shown in the figures below.
When the oven temperature reaches the predetermined tem-
perature, the digital programmer circuit stops supplying power
to relay (RY5) resulting in the convection heater turning off.
During this time the digital programmer circuit continues to
operate relay (RY1) so that microwave activity continues at the
duty cycle selected. The inverter control signal level is also
maintained. The microwave activity continues to cycle until the
entire cooking program is completed.
When the oven temperature drops below the selected tempera-
ture, the digital programmer circuit operates power relay (RY5)
switching on the heater elements.
In the case of grill combination the sequence applies with the
digital programmer circuit switching power relay (RY4) to con-
trol, the grill elements.
With convection, grill and micro power combination. The grill
elements and convection elements are operated alternatively
whilst the oven temperature is above the selected level.
Convection And Microwave Combination Duty Cycles
Grill And Microwave Combination Duty Cycles
Grill Convection And Microwave Combination Duty Cycles
Convection And Microwave Duty Cycles
Figure 1
Convection Heater Micropower
100 - 250 C OUTPUT ON OFF
Medium 600W 22 0
Low 440W 22 0
Simmer 440W 14 8
Warm 440W 7 15
Grill Heater Micropower
ON OFF OUTPUT ON OFF
Grill 1 66 0 Medium 600W 22 0
Grill 2 48 18 Low 440W 22 0
Grill 3 36 30 Simmer 440W 14 8
Warm 440W 7 15
Convection
Heater
Grill Heater Micropower
100 - 250 C ON OFF OUTPUT ON OFF
Grill 1 66 0 Medium 600W 22 0
Grill 2 48 18 Low 440W 22 0
Grill 3 36 30 Simmer 440W 14 8
Warm 440W 7 15