Panasonic NN-A720MB Service Manual Download Page 1

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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

tion is a violation of law.

Summary of Contents for NN-A720MB

Page 1: ...0W 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 ...

Page 2: ...ages 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 whil...

Page 3: ...3 3 Control Panels ...

Page 4: ... 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 standi...

Page 5: ...s 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 tem...

Page 6: ...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 ...

Page 7: ...7 5 Schematic Diagram 6 Wiring Diagram ...

Page 8: ...mines 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 predet...

Page 9: ...er 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 a...

Page 10: ...ow 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...

Page 11: ...11 Grill and Microwave Duty Cycles Figure 2 Grill Convection And Microwave Duty Cycles ...

Page 12: ...12 Figure 3 ...

Page 13: ...V Inverter warning Figure 1 WARNING FOR INVERTER POWER SUPPLY U GROUND ING Check the high voltage inverter power supply circuit grounding 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 volt ages and cause extreme DANGER Be sure that...

Page 14: ...epair 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...

Page 15: ...nnector CN701 and CN702 from the inverter PCB 6 Remove the two screws holding the inverter base to the chassis See figure 2 7 Carefully remove the inverter PCB and support base from the oven 8 Remove the air guide E by un clipping the catch hooks 9 Remove the four screws holding the PCB to the inverter support base Caution when replacing the inverter power supply U 1 Make sure that grounding plate...

Page 16: ...a 30W sol dering iron carefully remove all solder from the terminal pins of the low voltage transformer and or power relays 2 With all of the terminal pins cleaned and separated from the DPC contacts remove the defective transformer power relays and install the new components making sure that the terminal pins are inserted completely Care fully re solder all terminal contacts carefully Note Do not...

Page 17: ...ly is not mounted properly microwave power may leak from the clearance between the door and oven 3 Perform the microwave leakage test Disassembly of the door Figure 7 Adjusting the door hinge Figure 8 9 7 Turntable Motor 1 Remove the motor cover by breaking off at the 8 spots indicated by the arrows 2 Disconnect the two lead wires connected to the turntable motor 3 Remove the turntable motor by re...

Page 18: ...18 One screw to remove the grill bracket Figure 11 Removing the grill element Figure 12 ...

Page 19: ...lding the convection assem bly push upwards to remove 6 To remove the convection element remove the one screw E on the convection bracket A and 2 screws D on convec tion bracket B 7 Release the circulation fan nut to remove the circulation fan blade 8 Remove the three screws F to release the circulation fan motor assembly Disassembly of the rear convection assembly Figure 13 9 10 Temperature Senso...

Page 20: ...ir cuit 1 Unplug the lead wires from the HV inverter primary termi nals 2 Connect the test probes of the ohm meter to these leads 3 Test the continuity of the short switch with the door open and the door closed using the lowest ohm scale 10 3 Magnetron Continuity checks can only indicate an open filament or a shorted magnetron To diagnose an open filament or shorted magnetron 1 Isolate the magnetr...

Page 21: ...10 7 Temperature Sensor A temperature sensor is mounted on the oven cavity on the right hand side The resistance reading across the thermistor should read 300K ohm within a temperature range of 10 to 30 degrees centigrade This would be the temperature range within a kitchen environment If the resistance measured is out side this range the thermistor is defective and should be replaced NOTE When me...

Page 22: ...he latch keys move smoothly after adjustment is completed Completely tighten the screws holding the door hook assembly to the oven assembly 3 Reconnect the short switch primary switch and second ary latch switches and check the continuity of the monitor circuit and latch switches by following the component test procedures on page 11 2 Measurement of microwave output The output power of the magnetr...

Page 23: ...To do otherwise may result in a false reading or damage to your meter When dis connecting a plastic connector from a terminal you must hold the plastic connector and not the lead wire otherwise the lead wire may become open circuit 7 Do not touch any parts of the circuitry on the digital programmer cicruit since static electric discharge may damage this con trol panel Whilst working on this board ...

Page 24: ...24 Troubleshooting Fuse is blown Figure 2 Troubleshooting Other problems Figure 3 ...

Page 25: ...25 Troubleshooting Inverter by Input out voltage Figure 4 Troubleshooting Inverter by Microwave Oven Input Current Figure 5 ...

Page 26: ...26 13 Digital Programmer Circuit Troubleshooting Guide How to test the semiconductors ...

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