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John Lewis NN-CT878SBJQ Service Manual

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

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Summary of Contents for John Lewis NN-CT878SBJQ

  • Page 1 HAD0901001C2 Microwave Oven NN-CT878SBJQ JLFSMWC003 32L OEM United Kingdom...

  • Page 2: Table Of Contents

    NN-CT878SBJQ JLFSMWC003 32L OEM 1 Contents Contents ............2 Inverter Warnings .

  • Page 3: Inverter Warnings

    NN-CT878SBJQ JLFSMWC003 32L OEM 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.

  • Page 4: Control Panel

    NN-CT878SBJQ JLFSMWC003 32L OEM 4 Control Panel Display Window Time Pads Auto Sensor Microwave Programs (4a) Auto Sensor Combination Programs (4b) Auto Weight Combination Programs Auto Weight Defrost Programs Microwave Power Pad Grill Pad AUTO SENSOR Reheat Meal Convection Pad...

  • Page 5: Operation And Digital Programmer Circuit Test Procedure

    NN-CT878SBJQ JLFSMWC003 32L OEM 5 Operation And Digital Programmer Circuit Test Procedure...
  • Page 6 NN-CT878SBJQ JLFSMWC003 32L OEM...
  • Page 7 NN-CT878SBJQ JLFSMWC003 32L OEM...

  • Page 8: Schematic Diagram

    NN-CT878SBJQ JLFSMWC003 32L OEM 6 Schematic Diagram...

  • Page 9: Wiring Diagram

    NN-CT878SBJQ JLFSMWC003 32L OEM 7 Wiring Diagram...

  • Page 10: Description Of The Operation Sequence

    NN-CT878SBJQ JLFSMWC003 32L OEM 8 Description of Operating instruction 8.1. Variable power cooking control 8.3. Auto weight defrost, Auto weight Cook The HIGH VOLTAGE INVERTER POWER SUPPLY controls the output power by a signal from the digital Programmer circuit When an auto control feature is selected and the start pad DPC.

  • Page 11: Convection Cooking

    NN-CT878SBJQ JLFSMWC003 32L OEM 8.4. Convection Cooking 1. The digital programmer circuit operates the power relays temperature, the digital programmer circuit supplies RY3,RY5 and RY6 in the sequence as shown in the figure power to power relay RY5 resulting in the convection below.

  • Page 12: Combination Cooking

    NN-CT878SBJQ JLFSMWC003 32L OEM 8.5. Combination Cooking Convection And Microwave Combination Duty Cycles Convection Heater Micropower Combination cooking is achieved by operating the microwave 100 - 250 C DISPLAY OUTPUT and heater modes together during one cooking cycle. There 360W are three combination modes.
  • Page 13 NN-CT878SBJQ JLFSMWC003 32L OEM 8.5.1 convection and microwave duty cycles Figure 1...
  • Page 14 NN-CT878SBJQ JLFSMWC003 32L OEM 8.5.2 grill and microwave duty cycles Figure 2...
  • Page 15 NN-CT878SBJQ JLFSMWC003 32L OEM 8.5.3 Grill,Convection and microwave duty cycles Figure 3...
  • Page 16 NN-CT878SBJQ JLFSMWC003 32L OEM 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- Category P1 POWER P2 POWER K FACTOR...

  • Page 17: Cautions To Be Observed When Troubleshooting

    NN-CT878SBJQ JLFSMWC003 32L OEM 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.
  • Page 18 NN-CT878SBJQ JLFSMWC003 32L OEM Inverter Grounding Figure 2 Discharging the high voltage capacitors Figure 3 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.

  • Page 19: Confirm After Repair

    NN-CT878SBJQ JLFSMWC003 32L OEM 9.3. When parts must be replaced, 9.6. Confirm after repair remove the power plug from 1. After repair or replacement of parts, make sure that the screws of the oven, etc. are neither loose nor missing.

  • Page 20: Part Replacement Procedure

    NN-CT878SBJQ JLFSMWC003 32L OEM 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.
  • Page 21 NN-CT878SBJQ JLFSMWC003 32L OEM 3. Securely connect the 3 lead wire connectors 4. Make sure that the heat sink has enough space (gap) from the oven. Take care not to touch any lead wire to the aluminium heat sink because it is hot.
  • Page 22 NN-CT878SBJQ JLFSMWC003 32L OEM Disconnecting the PCB lock connector Removal of DPC DU and DPC AU Figure 4 Figure 5 10.3. Digital Programmer Circuit (DPC) membrane board. NOTE: Ground any static electric built up on your body before handling the DPC.

  • Page 23: Fan Motor

    NN-CT878SBJQ JLFSMWC003 32L OEM 10.5. Fan Motor proper installation and adjustment so as to prevent exces- sive microwave leakage. 1. Disconnect the two lead wires from the fan motor termi- 1. When mounting the door to the oven, be sure to adjust...

  • Page 24: Quartz Heater

    NN-CT878SBJQ JLFSMWC003 32L OEM Note: After breaking off the motor cover, make sure that cut-off portions are properly trimmed off or bent inside so that no sharp edges are exposed. Note: To secure the motor cover use a 4 x 6 screw.
  • Page 25 NN-CT878SBJQ JLFSMWC003 32L OEM Removing the screws holding the grill heater Figure 11 Removing the grill element Figure 12...
  • Page 26 NN-CT878SBJQ JLFSMWC003 32L OEM 10.9. Convection Element And Circulation Fan Motor 1. Remove one screw to remove the exhaust guide D. Figure 13. 2. Remove the rear heater cover by removing the three screws. Figure 13 3. Remove the temperature sensor by removing the two screws. Figure 14 4.
  • Page 27 NN-CT878SBJQ JLFSMWC003 32L OEM Removing the oven back plate Figure 14 Removing the base plate Figure 15...
  • Page 28 NN-CT878SBJQ JLFSMWC003 32L OEM Removing the circulation motor Figure 16...

  • Page 29: Component Test Procedure

    NN-CT878SBJQ JLFSMWC003 32L OEM 11 Component Test Procedure Caution 1. High voltage is present at the high voltage terminal of the inverter unit, including the aluminium heat sink. 2. It is not necessary or advisable to attempt to measure this high voltage.
  • Page 30 NN-CT878SBJQ JLFSMWC003 32L OEM 11.5. Inverter Power Supply Caution DO NOT try to repair this inverter power supply. Replace as a whole H.V. Inverter Unit. Inverter power supply diagram Figure 3 11.6. Inverter Power Supply Unit sor is working, perform the following test.

  • Page 31: Measurements And Adjustments

    NN-CT878SBJQ JLFSMWC003 32L OEM 12 Measurements and Adjustments Warning • For continued protection against radiation hazard, replace only with identical parts. • When the 10 amp fuse is blown due to the operation of the short switch, you must replace the primary latch switch and short switch.

  • Page 32: Troubleshooting Guide

    NN-CT878SBJQ JLFSMWC003 32L OEM 13 Troubleshooting Guide...
  • Page 33 NN-CT878SBJQ JLFSMWC003 32L OEM Fuses are blown Fuses are not blown...
  • Page 34 NN-CT878SBJQ JLFSMWC003 32L OEM Other problems Inverter circuit troubleshooting 6A5BPQ Alternative method for toubleshooting, the inverter circuit 6A5BPQ...

  • Page 35: Digital Programmer Troubleshooting Guide

    NN-CT878SBJQ JLFSMWC003 32L OEM 14 Digital Programmer Troubleshooting Guide...
  • Page 36 NN-CT878SBJQ JLFSMWC003 32L OEM...

  • Page 37: Description Of Operating Instruction

    NN-CT878SBJQ JLFSMWC003 32L OEM 15 Description of Operating instruction 15.1. 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.

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