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Panasonic NN-A720MB, Manual

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Panasonic NN-A720MB Manual Download Page 41

4. The normal temperature rise at the high power position for each 

model is shown in the table. (Figure 2)

Figure 1

Adjustment of latch switch assembly

RATED OUTPUT

TEMPERATURE 

RISE

1000W

8°C

12.  Troubleshooting guide

Caution

1. Do not try to repair this H.V. Inverter power supply. Replace as a 

whole unit. When returning the inverter unit pack in the original 
inverter box.

2. Do not adjust the preset volume on the H.V. Inverter. It is very 

dangerous to repair or adjust without sufficient test equiptment, 
this circuit handles very high volatge and current

3. Ensure a good ground connection before beginning any 

troubleshooting

4. Be careful of the high voltage circuit and take necessary 

precautions when troubleshooting 

5. Discharge the high voltage capacitors on the inverter.

41

Summary of Contents for NN-A720MB

Page 1: ...Order Number MOP00080014C2 Microwave Oven NN A750WB NN A720MB NN A770SB 27L WHITE SILVER STAINLESS United Kingdom SPECIFICATIONS Specification 1 ...

Page 2: ...0W 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 distribution is a violation of law 2 ...

Page 3: ...ns very high voltages 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 ful...

Page 4: ...ven 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 Figure 1 Inverter Power Supply Diagram Figure 2 Inverter Layout 2 Feature Chart 4 ...

Page 5: ...wave 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 Control Panels 5 ...

Page 6: ...4 Operation And Digital Programmer Circuit 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 6 ...

Page 7: ...Cooking 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 7 ...

Page 8: ...has elapsed oven automatically switches to second stage 8 When second stage cooking has elapsed oven bleeps 5 times and shuts off 4 3 Auto Weight Defrost 1 Select the desired program 2 Press g or lb and oz 3 Enter the weight by pressing the Up Down Pads 8 ...

Page 9: ...4 Press Start 4 4 Delay Stand 1 Set power level and time 2 Press Stand 3 Set standing time 4 Press Start 4 5 Delay Start 1 Press delay 2 Set delay time 3 Set power level and time 9 ...

Page 10: ...Operation 1 Select grill power press once for grill 1 2 Set cooking time 3 Press start 4 7 Convection Operation 1 Press convection pad to select oven temperature 2 Press start to preheat 3 Press time pads to enter cooking time 10 ...

Page 11: ...s start pad 4 8 Turbo Bake Operation 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 11 ...

Page 12: ...ombination Cooking Convection And Microwave 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 12 ...

Page 13: ...ation Cooking Grill And Microwave 1 Press combination pad 2 Press grill pad to select oven temperature 3 Select micro power 4 Set cooking time 5 Press start pad 4 11 Combination Cooking Turbo Bake And Microwave 13 ...

Page 14: ...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 14 ...

Page 15: ... 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 5 Schematic Diagram 15 ...

Page 16: ...16 ...

Page 17: ...6 Wiring Diagram 17 ...

Page 18: ...e 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 Output Duty ON OFF ON time OFF time High 1000W 22 0 Defrost 440W 16 6 Medium 600W 22 0 Low 440W 22 0 Sim...

Page 19: ... 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 Cat...

Page 20: ...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 pow...

Page 21: ...ime 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 temperature the digital programmer circuit operates power relay RY5 switching ...

Page 22: ...cropower 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 Grill Convection And Microwave Combination Duty Cycles Convection Heater Grill Heater Micropower 100 250 C ON OFF OUTPUTON 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 Figure 1 22 ...

Page 23: ...Convection And Microwave Duty Cycles Figure 2 Grill and Microwave Duty Cycles Figure 3 23 ...

Page 24: ...nsure the appliance is properly grounded before beginning repair work 8 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 lik...

Page 25: ... 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 powe...

Page 26: ...ment voltage of the magnetron WARNING Never touch any circuit wiring with your hand nor with an insulated tool during operation 8 3 When parts must be replaced remove the power plug from the outlet 8 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...

Page 27: ... 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 inv...

Page 28: ...e 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 Figu...

Page 29: ...ping 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 is in place 2 Securely tighten the grounding screw through the side of the chassis Base 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 an...

Page 30: ...bly To remove escutcheon pad 1 Remove the escutcheon bracket from the escutcheon base by freeing the 4 catch hooks on the escutcheon base 2 Peel away the display window from the inside of the base 3 Remove the membrane assembly by pushing from the inside of the base and then peeling away from the outside surface NOTE 1 The escutcheon key board is attached to the escutcheon base with double faced a...

Page 31: ...ound your body to discharge any static before handling the DPC 1 Using a solder wick or a de soldering tool and a 30W soldering 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 ...

Page 32: ...rifice assembly 7 Remove the two screws holding the fan motor assembly 8 Detach the orifice assembly and the fan motor assembly from the oven assembly 9 Remove the fan blade from the fan motor by pulling outward Figure 6 Removing the fan motor 9 6 Door disassembly 1 Remove door C from door E by carefully pulling outward starting from the upper right hand corner using a flat blade screwdriver 2 Rem...

Page 33: ... door parallel to the bottom line of the oven face plate by moving the upper hinge in the direction necessary for proper alignment 2 Adjust so that the door has no play between the inner door surface and the oven front surface if the door assembly is not mounted properly microwave power may leak from the clearance between the door and oven 3 Perform the microwave leakage test Figure 7 Disassembly ...

Page 34: ...t 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 Figure 9 Removing the turntable motor cover Figure 10 Two screws to remove the turntable motor 9 8 Quartz Heater 1 Disconnect the lead wires from the heater terminals 2 Remove one screw holding the heater supports 3 Remove the heater Figure 11 34 ...

Page 35: ...d the convection elements 3 After removing the rear heater cover remove the three screws B holding the inner heater cover 4 Un clip the metal tags to remove the inner heater cover 5 Remove the two screws C holding the convection assembly 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 convection bracket B 7 Release the ...

Page 36: ...ssembly of the rear convection assembly 9 10 Temperature Sensor 1 Remove lead wire plug from connector CN7 2 Remove 1 screw holding temperature sensor 3 Replace temperature sensor and lead wire as a complete unit Figure 14 Removing the temperature sensor unit 10 Component Test Procedure 36 ...

Page 37: ...plug the lead connectors to the primary latch switch and secondary latch switch 3 Test the continuity of the switches with the door open and closed with an ohm meter on the lowest scale Normal continuity readings should be as followed Door Open Door Closed Primary Latch Switch infinite Open 0 Close Secondary Latch switch infinite Open 0 Close Power relay B infinite Open infinite Close 10 2 Short S...

Page 38: ...minals should indicate one ohm or less 3 A continuity check between each filament terminal and the magnetron case should read open 10 4 Push Button Keyboard Check the continuity between the switch terminals by tapping an appropriate pad on the keyboard The keypad matrix is shown on Key Board Matrix 10 5 Inverter Power Supply Caution DO NOT try to repair this inverter power supply Replace as a whol...

Page 39: ... resistance measured is outside this range the thermistor is defective and should be replaced NOTE When measuring the resistance of the thermistor disconnect the connector from the digital programmer circuit NOTE If the microwave oven has been operated allow to cool to room temperature before attempting to measure the thermistor resistance 11 Measurements and Adjustments Warning For continued prot...

Page 40: ...mbly to the oven assembly 3 Reconnect the short switch primary switch and secondary 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 magnetron can be determined by performing the IEC standard test However due to the complexity of the IEC test procedures i...

Page 41: ...s a whole unit When returning the inverter unit pack in the original inverter box 2 Do not adjust the preset volume on the H V Inverter It is very dangerous to repair or adjust without sufficient test equiptment this circuit handles very high volatge and current 3 Ensure a good ground connection before beginning any troubleshooting 4 Be careful of the high voltage circuit and take necessary precau...

Page 42: ...er cicruit since static electric discharge may damage this control panel Whilst working on this board ensure that that your body is connected to ground to discharge any static charge 8 240 VAC is present on the digital programmer circuit Terminals of the power relays and the primary circuit of the low voltage transformer When troubleshooting be cautious of possible electric shock Before troublesho...

Page 43: ...Troubleshooting Fuse is blown Figure 3 Troubleshooting Other problems Figure 4 Troubleshooting Inverter by Input out voltage 43 ...

Page 44: ...Figure 5 Troubleshooting Inverter by Microwave Oven Input Current 13 Digital Programmer Circuit Troubleshooting Guide 44 ...

Page 45: ...Figure 2 How to test the semiconductors 14 Main Parts List 45 ...

Page 46: ...8BN Screws 3 10 E66804V00BP Heater Cover B 1 11 E22424V00BP Adiabatic Material A 1 12 E490S4V00BP Circulation Fan Motor 1 13 E41804V00BP Motor Bracket 1 14 XTBANE 4 8BN Screws 3 15 E41594V00BP Cooling Fan 1 16 E41614V00BP Fan Spacer A 1 17 XTWANE 4 8BN Screws 3 18 XTBANE 4 8BN Screws 2 19 E66794V00BP Heater Cover A 1 20 E630H4V00BP Heater Unit 1 21 E22394V00BP Circulation Fan 1 22 E41634V00BP Fan ...

Page 47: ...P Air Guide E 1 62 E09020000AL Cushion Rubber 1 63 E10014N30BP Base Plate 1 64 E09270000AH Cushion Rubber 1 65 E09270000AM Cushion Rubber 1 66 E1008 1180 Rubber Foot 4 67 E09270000AM Cushion Rubber 1 68 XTWA 4 12CF Screws 6 69 E110D4V00HBP Outer Panel 1 NN A750WB 69 E110D4V00NBP Outer panel NN A720MB 69 E110D4V00SBP Outer Panel NN A770SB 70 XTW 3 6B Screws 2 71 E63268960JP Turntable Motor 1 72 E01...

Page 48: ...L Cushion Rubber 1 91 XTWANE 4 8BN Screw 1 92 E605A 1960 Temperature Sensor 1 93 E900C6520BP Power cord 1 94 E030E4N30BP H V Lead Wire 1 95 E90314V00BP Holder 1 96 E90314VOOBP Holder 1 97 E67579000BP Heater bracket D 1 98 E203B4V00SBP Heater Cover 1 NN A770SB 99 E01504V00SBP Warning label 1 NN A770SB 15 Exploded View 48 ...

Page 49: ...49 ...

Page 50: ...50 ...

Page 51: ...16 Door Assembly 51 ...

Page 52: ...52 ...

Page 53: ...53 ...

Page 54: ... NN A750WB D2 E30014V00NBP Door A 1 NN A720WB D3 E30214000AP Door Key Spring 1 D4 E30184L00GS Door Key 1 D5 E31464V00BP Door Screen B 1 D6 E302K4V00BP Door E 1 D7 E30854V00BP Door Screen C 1 NOTE When ordering any Door component also order door C as this part may become damaged during disassembly 17 Escutcheon Base 54 ...

Page 55: ...55 ...

Page 56: ...56 ...

Page 57: ... NN A720MB E8 E81274L10BP Back plate 1 NN A750WB NN A720MB E8 E81274V00SBP Back plate 1 NN A770SB E9 E603L4V00BP DPC AU 1 E10 E66164L00GS Ribbon cable 1 E11 E82564L10BP Door opening lever 1 NN A750WB NN A720MB E11 E82564V00SBP Door opening lever 1 NN A770SB E12 E603Y4V00BP DPC DU 1 E13 E607044V00SBP Insulation sheet 1 NN A770SB E14 E83264V20BP Display sheet 1 E15 E00074V00BP Name plate 1 NOTE Plea...

Page 58: ...58 ...

Page 59: ... 1 P8 E290D4N00BP Roller ring 1 P9 E01695750BP Service center list 1 P10 E00034V00BP Operating instructions and cook book 1 P11 E01134N30BP Tray styrol 1 P12 E01024V00HBP Carton box 1 NN A750WB P12 E01024V00NBP Carton box 1 NN A720MB P12 E01024V00SBP Carton box 1 NN A770SB P13 E01054V00BP Lower filler 1 P14 E01076700BP Door sheet 1 P15 E01066750BP Vinyl Cover 1 P16 E01926430GP Protector sheet 1 NN...

Page 60: ...P NN TKA70 E1603A510NBP 1 E1601A510NBP NN A720MB INSTALLATION GUIDE E000QA820BP 20 Noise filter component parts Ref No Part No Part Name Description Qty Remarks R1 ERG1SJ753P Resistor 1 75KW W C1 C2 QETJ5225KRP2CE Capacitor 2 2 2mF C3 C4 ECKMNA472ME Capacitor 2 4700pF 250V AC L1 SC 08 E203A Inductor 1 2 4mH F1 E62316010BP Fuse Holder 2 21 Digital programmer Circuit 60 ...

Page 61: ...DPC Schematic 1 61 ...

Page 62: ...62 ...

Page 63: ...DPC Schematic 2 22 Key Board Matrix 23 Digital programmer circuit parts list 23 1 E603L4L00BP DPC AU 63 ...

Page 64: ...EM19FESVKN CONNECTOR 1 IC220 AN6747B Custom IC 1 23 2 E603Y4V00BP DPC DU Ref No Part No Description Qty Remarks ZD10 AESZMTZ5R6B Zener Diode 1 D221 D224 AESS133T 77 Silicon Diode 4 D25 AESS133T 77 Silicon Diode 1 D220 AESS1N4003E Silicon Diode 1 C330 ECBT1H681KB5 Capacitor 1 680PF C440 ECBT1E103ZF5 Capacitor 1 10nF R25 R26 ERDS1FJ563T Resistor 2 56K 1 2 Watt R220 R232 ERDS2TJ103T Resistor 2 10K R1...

Page 65: ...5G1A12 12 V Relay 3 CN5 AEEM19FEBVKN 19 Pin Connector 1 CN1 AEEMXD55511W 11 Pin Connector 1 IC25 AEICP25011HL Photocoupler IC 1 D26 AESTS1WBA60B Diode Bridge 600V 1 C25 ECA2WHG100E Electrolytic Capacitor 1 10uF 450V BZ310 EFBAH20C001 2KHz Buzzer 1 D2 D3 ERZV10D112C1 Varistor 2 1100V D1 ERZV10D511CS Varistor 1 510V IC10 ETXMJ197X1BG Switching Power Supply 1 S 4V00BP SM 65 ...

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