John Lewis NN-CT878SBJQ User manual

HAD0901001C2
Microwave Oven
NN-CT878SBJQ
JLFSMWC003
32L OEM
United Kingdom

NN-CT878SBJQ JLFSMWC003 32L OEM
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1 Contents
1 Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Inverter Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Feature Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
4 Control Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
5 Operation And Digital Programmer Circuit Test Procedure . . . . . . . . . . . . . . . . . . . 5
6 Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7 Wiring Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8 Description of the Operation Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9 Cautions to be Observed when Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
10 Part Replacement Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
11 Component Test Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
12 Measurements and Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
13 Troubleshooting Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
14 Digital Programmer Troubleshooting Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
15 Description of Operating instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
16 Exploded View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
17 Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
18 Door Assy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
19 Escutcheon Base. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
20 Packing and Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
21 Digital Programmer Circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
22 Key Board Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
© Panasonic Home Appliance Division. 2008
Unauthorized copying and distribution is a
violation of law.

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2 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 without a proper ground connection.
Inverter Grounding
Figure 1
Inverter PCB layout
Figure 2
3 Feature Chart
Function NN-A883
Microwave 6
Grill 3
Convection 17
Combination YES
Sensor reheat 2
Sensor cook 2
Sensor combination 4
Sensor crisp -
Weight defrost 3
Weight combination 8
Weight reheat -
Weight cook -
Memory cook -
Weight crisp -
Stage cooking 3
Delay/Stand YES
More/Less YES
Kg-> lb/oz YES
Clock 12H
Word prompt English
Step by Step LED

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4 Control Panel
Potatoes
Micro Power
Grill 1-2-3
Convection
Turbo-Bake
Combination
CHAOS
g/ lb
oz
Delay/
Stand Clock more less
Stop/Cancel Start
Reheat
Meal
Pastry/
Cake
Crispy
Top
Meat
Chicken
Roast Veg
Veg/Fish
JLFSMWC003
AUTO SENSOR
SENSOR COMBI
AUTO WEIGHT
10
min
1
min
10
sec
1
h
(1) Display Window
(2) Time Pads
(3) Auto Sensor Microwave
Programs
(4a) Auto Sensor Combination
Programs
(4b) Auto Weight Combination
Programs
(5) Auto Weight Defrost Programs
(6) Microwave Power Pad
(7) Grill Pad
(8) Convection Pad
(9) TURBO-BAKE Pad
(10) Combination Pad
(11) Delay/Stand Pad:
This can be used to delay a
cooking program for up to 9 hrs
99 mins., or used to time or for
standing (non-cooking) time.
(12) Clock Pad:
Refer to page 15 for setting the
clock.
(13) lb/oz Conversion Pad
(14) More/Less Pads
(15) Stop/Cancel Pad:
Before Cooking:
one press clears your instructions.
During Cooking:
one press temporarily stops the
cooking program. Another press
cancels all your instructions and
the time of day will appear in the
display.
(16) Start Pad:
Press to start operating the oven.
If during cooking the door is
opened or Stop/Cancel Pad is
pressed once, Start Pad has to
be pressed again to continue
cooking.
(17) Door Release Pad
(1)
(2)
(15)
(12)
(13)
(14)
(16)
(6)
(7)
(8)
(9)
(10)
(5)
(11)
(3)
(4a)
* The design of your control panel may
vary from the panel displayed (depending
on colour and shape of pads or buttons),
but the words relating to the pads will be
the same, and function in the same way.
(4b)
(17)

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5 Operation And Digital Programmer Circuit Test Procedure

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6 Schematic Diagram

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7 Wiring Diagram

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8 Description of Operating instruction
8.1. 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 from 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
8.2. 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
8.3. 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.
Defrost Menu’s
Weight Menu’s
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 66” 0”
Grill 2 54” 12”
Grill 3 42” 24”
Category 1st Touch Weight Cooking Time
Turbo Defrost 500g 8m 20s
Category 1st Touch Weight Cooking Time
1. Whole Chicken 1000g 18m 20s
2. Chicken Pieces 300g 9m 30s
3. Beef / Lamb 500g 14m 40s
4.Casserole 800g 56m 40s
5. Pastry 600g 15m 00s
6. Cake 400g 11m 40s

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8.4. Convection Cooking
1. The digital programmer circuit operates the power relays
RY3,RY5 and RY6 in the sequence as shown in the figure
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
Figure 1

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8.5. 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 operates 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 Heater Micropower
100 - 250 C DISPLAY OUTPUT ON OFF
440 360W 66 0
250 360W 48 18
100 360W 21 45
Grill Heater Micropower
ON OFF DISPLAY OUTPUT ON OFF
Grill 1 51 15 440 360W 66 0
Grill 2 42 24 250 360W 48 18
Grill 3 28 38 100 360W 21 45
Convection
Heater
Grill Heater Micropower
100 - 250 C ON OFF OUTPUT ON OFF
Grill 1 51 15 440 360W 66 0
Grill 2 42 24 250 360W 48 18
Grill 3 28 38 100 360W 21 45

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8.5.1 convection and microwave duty cycles
Figure 1

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8.5.2 grill and microwave duty cycles
Figure 2

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Figure 3
8.5.3 Grill,Convection and microwave duty cycles

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8.6. One touch Auto sensor cooking
Auto sensor cook is a revolutionary way to cook by microwave
without setting a power level or selecting a time. All that is nec-
essary 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 fea-
tures. 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 humid-
ity sensor heater is on.
2. During the 30 second period there is no microwave activ-
ity. 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 con-
tainer 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 micro-
processor memory and they are listed in the following
tables along with the P1 and P2 power.
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 selected is sensor
reheat. Fish (Program 4)
T2 = T1 x K
= 2 min. and 40 sec. X. 0.3
=48 sec.
Auto sensor cooking
Figure 1
Category P1 POWER P2 POWER K FACTOR
STANDARD
1. Chilled meal HIGH HIGH 1.6
2. Frozen meal MED HIGH 0.9

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9 Cautions to Be Observed When Troubleshooting
Unlike many other appliances, the microwave oven is a high
voltage, high current device. Although 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.
9.1. 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.
9.2. 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 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 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 con-
nected. 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.
WARNING FOR INVERTER POWER SUPPLY (U) GROUND-
ING
Check the high voltage inverter power supply circuit ground-
ing. This 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.
HV Inverter warning
Figure 1

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WARNING! DISCHARGE THE HIGH VOLTAGE CAPACI-
TORS
For about 30 seconds after the oven is turned off, an elec-
tric 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 nor with an
insulated tool during operation.
Inverter Grounding
Figure 2
Discharging the high voltage capacitors
Figure 3

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9.3. When parts must be replaced,
remove the power plug from
the outlet.
9.4. 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 con-
tacts.
1. This is mandatory. Refer to “adjustments and measure-
ments” for the location of these switches.
2. When replacing the fuse, confirm that it has the appropri-
ate 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.
9.5. 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 leak-
age.
9.6. 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 tight-
ened.
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 proce-
dure for measuring microwave energy leakage).
CAUTION MICROWAVE RADIATION
DO NOT BECOME EXPOSED TO RADIATION FROM THE
MICROWAVE GENERATOR OR OTHER PARTS CON-
DUCTING MICROWAVE ENERGY
IMPORTANT NOTICE
The following components have potentials above 250V
while the appliance is in operation.
• 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.
9.7. 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.

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10 Parts Replacement Procedure
10.1. Magnetron
1. Discharge the high voltage capacitors on the inverter cir-
cuit.
2. Remove the five screws shown in figure 1
3. Disconnect the two high voltage leads from the magne-
tron
4. Remove the four screws holding the magnetron as shown
in figure 2
NOTE: After replacing the magnetron, tighten the mount-
ing screws making sure that there is no gap between the
waveguide and the magnetron to prevent microwave leak-
age.
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 magnetron as
listed in the parts list.
Removal of the magnetron
Figure 1