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6. PARTS REPLACEMENT PROCEDURE

6.1 Magnetron

1. Discharge the high voltage capacitor.
2. Disconnect 2 high voltage lead wires from the magnetron

filament terminals.

3. Remove 1 screw holding the magnetron.

NOTE: After replacement of the magnetron, tighten

mounting screws properly making sure trhere is
no gap between the waveguide and the mag-
netron to prevent microwave leakage.

6.2 Digital Programmer Circuit (DPC) and mem-

brane keyboard

NOTE: Be sure to ground any static electric charge built

up on your body before handling the DPC.

1. Disconnect all electrical connectors to the DPC.
2. Remove 2 screws holding escutcheon base and mem-

brane earth tail to oven chassis and slide the escutcheon
base upward slightly.

3. Release CN2 connector’s lock of the DPC by pushing

both levers from inside and pull them upward, the remove
the flat cable of the membrane keyboard.

4. Remove 3 screws holding the DPC.

To replace membrane switch keyboard

1. Push the upper part of the keyboard (display window por-

tion) from the back of the escutcheon base and peel off
the membrane keyboard completely from the escutcheon
base.

NOTE 1:  The membrane keyboard is attached to the

escutcheon base with double sided adhesive
tape. 

Therefore, applying hot air e.g. using a hair dryer
is recommended for smoother removal.

NOTE 2:  When installing new membrane keyboard,

make sure that the surface of the escutcheon
base is cleaned sufficiently so that any problems
(shorted contacts or uneven surface) can be
avoided.

NOTE 3: Alignment position of membrane keyboard and

escutcheon sheet are as follows: 

Membrane keyboard: Right and lower edges,
Escutcheon sheet: Right and lower adges.

6.3 Low  voltage transformer and/or power

relays

NOTE: Be sure to ground any static electric charge built

up on your body before handling the DPC.

1. Using solder wick or a desoldering tool and 30W solder-

ing iron, carefully remove all solder from the terminal pins
of the low voltage transformer and/or power relays.

NOTE: Do not use a soldering iron or desoldering tool

of more than 30 watts on DPC contacts.

2. With all the terminal pins cleaned and separated from

DPC contacts, remove the defective transformer/power
relays and install new transformer/power relays making
sure all terminal pins are inserted completely. Resolder
all terminal contacts carefully.

6.4 Oven thermostat

1. Disconnect 2 lead wires from thermal cut-out
2. Draw froward the oven thermostat

CAUTION

When replacing the magnetron, be sure the antenna gas-
ket is in place.

MAGNETRON

SCREW

Summary of Contents for NN-E251W

Page 1: ...L Outside Dimensions 465mm W X 346mm D X 279mm H Inside Dimensions 290mm W X 306mm D X 220mm H Weight 12 5 kg Specifications subject to change without notice Specifications 2001 Matsushita Electric Industrial Co Ltd All rights reserved Unauthorized copying and distribution is a violation of law Order number MOP0105003C2 Microwave Oven NN E251W Service Manual ...

Page 2: ...ed repair technicians only and is not designed for use by the general public It Does not contain warnings or cautions to advise non technical individuals of potential dan gers in attempting to service a product Products powered by electricity should be serviced or repaired only by experienced professional technicians Any attempt to service or repair the product dealt with in the service informatio...

Page 3: ...our instructions During cooking one press temporarily stops the cooking program Another press can cels all your instructions and the time of day will appear in the display 10 start pad BEEP SOUND When a pad is touched correctly a beep will be heard If a pad is touched and no beep is heard the unit has not or cannot accept the instruction At the end of any complete program the oven will beep 5 time...

Page 4: ...times Press twice Press Clock pad Press Time pads Press Clock pad Display will show 12H Enter time of day by pressing appropriate time pads Numbers stop blinking When you press any number pads numbers will start blinking Press the pad with the power Select cooking time by pressing Press Start you require appropriate pads The cooking program will start and the time in the display will count down Pr...

Page 5: ...econds by DPC 4 During standing periods power relay B energized for 5 seconds and de energized for 24 seconds by DPC NOTE Defrosting time selected is converted into cer tain percent by the DPC but the display will show selected time in minutes and seconds as programmed The total number of seconds is divided into 5 different periods Example 2 If Defrosting time is selected for 10 minutes each opera...

Page 6: ... 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 other holes or gaps because such objects may work as an antenna and cause microwave leakage 5 7 5 8 CAUTION Servicemen should remove their watches whenever working close to or replacing the magnetron WARNING Never operate the ...

Page 7: ... the escutcheon base with double sided adhesive tape Therefore applying hot air e g using a hair dryer is recommended for smoother removal NOTE 2 When installing new membrane keyboard make sure that the surface of the escutcheon base is cleaned sufficiently so that any problems shorted contacts or uneven surface can be avoided NOTE 3 Alignment position of membrane keyboard and escutcheon sheet are...

Page 8: ...and adjustment so as to prevent an excessive microwave leakage 1 When mounting the door to the oven be sure to adjust the door parallel to the bottom line of the oven face plate by moving the upper hinge and lower hinge in the direc tion necessary for porper alignment 2 Adjust so that the door has no play between the inner door surface and oven front surface If the door assembly is not mounted pro...

Page 9: ...uity check between each filament terminal and magnetron case should read open 7 4 Diode 1 Isolate the diode from the circuit by disconnecting the leads 2 With the ohmmeter set the highest resistance scale measure the resistance across the diode terminals Reverse the meter leads and again observe the resis tance reading Meter with 6V 9V or higher voltage batteries should be used to check the front ...

Page 10: ...l protector exceeds its temperature it will turn off the power to oven cavity and display will go to reset mode The cooking program can be reset after cool down 7 7 HV Fuse 1 Isolate the HV Fuse assembly from the circuit by discon necting its leads 2 With the ohmmeter set at the highest resistance scale measure the resistance across the HV fuse terminals A normal HV fuse resistance will be 0Ω It i...

Page 11: ...rocedures it is recommended to test the magnetron using the simple method outlined below Necessary equipment 1 Iitre beaker Glass thermometer Wrist watch or stopwatch NOTE Check the line voltage under load to ensure it meets specifications Low voltage will cause reduction in the magnetron output Temperature readings and heating time should be as accurate as possible Output power performance test p...

Page 12: ...d Fuse is OK No display and no operation at all 2 Oven does not accept key input program 3 Oven lamp and turntable motor turn on when oven is plugged in with door closed 4 Timer starts countdown but no microwave oscillation 1 Open or loose lead wire harness 2 Open oven thermostat 3 Open low voltage transformer 4 Defective DPC 1 Key input is not in sequence 2 Open or loose connection of mem brane k...

Page 13: ...bles SYMPTOMS CAUSE CORRECTIONS 1 Microwave output is low Oven takes longer time to cook food 2 Turntable motor and oven lamp turn on when door is opened 3 Oven does not operate 4 Loud buzzing noise can be heard 5 Oven stops operation during cooking 6 Turntable motor does not rotate 1 Decrease in power source voltage 2 Open or loose wiring of magnetron filament circuit Intermittent oscilla tion 3 ...

Page 14: ...set and the start pad is tapped No microwave oscillation at 1 IC 1 pin 8 voltage while operation Abnormal IC 1 any power setting at high power Normal 5V RY1 Q10 D3 Dark or unclear display 1 Replace display and check operation Normal DISPLAY Abnormal IC 1 Missing or lighting of 1 Q1 Q7 check operation Normal Step 2 unnecessary segment Abnormal Q1 Q7 2 Replace IC 1 and check operation Normal IC 1 Ab...

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