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Drawer Microwave

(Models MWD24-2 / MWD30-2)

Troubleshooting Guide

5-2

#813632 - Revision B - December, 2009

TROUBLESHOOTING AND TECHNICAL DATA

This section of the manual Component Test Procedures.

NOTE:

Before continuing, please take note of the 

WARNINGS

 and 

CAUTIONS

 below.

• TO AVOID ELECTRIC SHOCK DURING TROUBLESHOOTING, NEVER TOUCH ANY PART OF THE ELECTRI-

CAL CIRCUIT WITH HANDS OR UN-INSULATED TOOLS WHILE THE POWER IS CONNECTED.

• MICROWAVE OVENS CONTAIN CIRCUITRY CAPABLE OF PRODUCING VERY HIGH VOLTAGE AND CUR-

RENT.  CONTACT WITH THE FOLLOWING COMPONENTS MAY RESULT IN SERIOUS PERSONAL INJURY OR
DEATH:

• TRANSFORMER • RECTIFIER • HIGH VOLTAGE HARNESS
• MAGNETRON

• CAPACITOR

NOTE:  THE CAPACITOR REMAINS CHARGED APPROXIMATELY 60 SECONDS AFTER THE OVEN IS
SWITCHED OFF.  WAIT FOR 60 SECONDS, THEN SHORT THE CAPACITOR TO THE CHASSIS.

• BEFORE SERVICING THE MICROWAVE OVEN, THE CAPACITOR MUST BE DISCHARGED BY SHORTING

THE CONNECTING LEAD OF THE RECTIFIER AGAINST THE CHASSIS WITH AN INSULATED SCREWDRIV-
ER.  FAILURE TO FOLLOW THIS STEP COULD RESULT IN SERIOUS PERSONAL INJURY OR DEATH.

• DO NOT OPERATE OR ALLOW THE OVEN TO BE OPERATED WITH THE DOOR OPEN.

Be careful when handling sheet metal parts - Edges may be sharp

.

NOTE:

When troubleshooting, it may be necessary in some cases to supply power to the unit with the outer cabinet

case removed (See CAUTION above).

In this event:

1.

Disconnect the power supply cord, and then remove outer cabinet case.

2.

Open the door and block it open.

3.

Discharge high voltage capacitor (See WARNING above).

4.

Disconnect the leads to the primary of the power transformer.

5.

Ensure that the leads remain isolated from other components and oven chassis by using insulation tape.

6.

Only after performing the five steps listed above should the power supply cord be reconnected.

When the testing is completed:

1.

Disconnect the power supply cord, then remove outer case.

2.

Open the door and block it open.

3.

Discharge high voltage capacitor.

4.

Reconnect the leads to the primary of the power transformer.

5.

Reinstall the outer cabinet.

6.

Reconnect the power supply cord after the outer case is installed.

7.

Run the oven and check all functions.

NOTES:

After performing any service to the Drawer Microwave, test to verify that there is no leakage of microwave ener-
gy (See next page).

Make the following safety checks on all ovens to be serviced before activating the magnetron or other microwave
source, and make repairs as necessary: 

Interlock operation

Proper drawer closing

Seal and sealing surfaces (arcing, wear, and other damage)

Evidence of dropping or abuse

Before turning on microwave power for any service test or inspection within the microwave generating compart-
ments, check the magnetron, wave guide or transmission line, and cavity for proper alignment, integrity, and con-
nections.

Summary of Contents for MWD24-2

Page 1: ...he outer cabinet case removed See CAUTION above In this event 1 Disconnect the power supply cord and then remove outer cabinet case 2 Open the door and block it open 3 Discharge high voltage capacitor See WARNING above 4 Disconnect the leads to the primary of the power transformer 5 Ensure that the leads remain isolated from other components and oven chassis by using insulation tape 6 Only after p...

Page 2: ...testing recommended instruments are NARDA 8100 and NARDA 8200 2 Place the load of 275 15 ml 9 8 oz of tap water initially at 20 5 C 68 F in the center of the oven cavity The water container shall be a low form of 600 ml 20 oz beaker with an inside diameter of approx 8 5 cm 3 1 2 in and made of an electrically non conductive material such as glass or plastic The placing of this standard load in the...

Page 3: ... The following symptoms indicate a defective keyboard unit When touching the pads a certain pad produces no signal at all When touching a number pad two figures or more are displayed When touching the pads sometimes a pad produces no signal If The Keyboard Unit is Defective 1 Disconnect the power supply cord and then remove covers 2 Open the drawer and block it open 3 Discharge high voltage capaci...

Page 4: ...ch stop switch operates properly that is the contacts are closed when the drawer is closed and open when the drawer is open If the door sensing switch stop switch is good disconnect the flat ribbon cable that connects the key unit to the control unit and make sure the drawer sensing switch is closed either close the drawer or short the door sensing switch connecter Use the Key unit matrix indicate...

Page 5: ...hese relays are operated by D C voltage Check voltage at the relay coil with a D C voltmeter during the microwave cooking operation DC voltage indicated Defective relay DC voltage not indicated Check diode which is connected to the relay coil If diode is good control unit is defective COMPONENT TEST PROCEDURE LETTER RELAY SYMBOL OPERATIONAL VOLTAGE CONNECTED COMPONENTS RY1 Approx 26 vdc Oven lamp ...

Page 6: ...n the oven cavity 2 Close the drawer touch the Defrost pad Then select Steaks Chops by touch ing the number pad 2 And touch the number pad 5 Now weight 0 5lb is set And then touch the start pad 3 The oven is in Defrost cooking condition 4 The oven will operate as follows WEIGHT 1ST STAGE 2ND STAGE 3RD STAGE LEVEL TIME LEVEL TIME LEVEL TIME 0 5 lb 60 20 sec 40 20 sec 30 45 sec 5 If improper operati...

Page 7: ...he troubleshooting guide given below if indicator does not light up after above check and repairs are finished Disconnect the power supply cord Remove the outer case cabinet Open the door and block it open Discharge high voltage capacitor Disconnect the leads to the primary of the power transformer Ensure that these leads remain isolated from other components and oven chassis by using insulation t...

Page 8: ...olvents near the oven while using Sensor settings The sensor will detect the vapor given of by the spray and turn off before food is properly cooked 8 If the sensor has not detected the vapor of the food ERROR will appear and the oven will shut off Water Load Cooking Test Make sure the oven has been plugged in at least two minutes before checking sensor cook operation The cabinet should be install...

Page 9: ...If new sensor does not operate properly the problem is with the control unit and refer to explanation be low CHECKING CONTROL UNIT 1 Disconnect the power supply cord and then disassemble as per Drawer Microwave Disassembly Section 4 Component Access Removal Page 4 6 2 Open the drawer and block it open 3 Discharge high voltage capacitor 4 Disconnect the sensor connector that is mounted to control p...

Page 10: ... Plunger NC NO COM COM NO NC R3 R4 R1 R2 1 2 3 F 1 F 2 F 3 To connector F on Control Unit CONNECTOR Refer to the Disassembly instructions found on page 16 G MAGNETRON ASSEMBLY TEST 1 Disconnect the power supply cord 2 Open the drawer and keep it open 3 To discharge high voltage capacitor wait for 60 seconds 4 To test for an open filament isolate the magnetron from the high voltage cir cuit A conti...

Page 11: ...d the temperature of the water 2 Place the cup of water in the oven Operate oven at POWER 10 HIGH selecting more than 60 seconds cook time Allow the water to heat for 60 seconds measuring with a stop watch second hand of a watch or the digital read out countdown 3 Remove the cup from the oven and again measure the temperature making sure to stir the thermometer or thermocouple through the water un...

Page 12: ...rd 2 Open the drawer and keep it open 3 To discharge high voltage capacitor wait for 60 seconds 4 Isolate the switch and connect the ohmmeter to the common COM and nor mally open NO terminal of the switch The meter should indicate an open circuit with the drawer open and a closed circuit with the drawer closed If improper operation is indicated replace the secondary interlock switch 5 Reconnect al...

Page 13: ...a closed circuit When the monitor switch actuator is pushed by a screw driver through the lower latch hole on the front plate of the oven cavity with the drawer opened in this condition the plunger of the monitor switch is pushed in the meter should indicate an open circuit If improper operation is indicated the switch may be defective and both the monitor switch plus fuse will need to be replaced...

Page 14: ...itor switch must be replaced with monitor fuse and monitor switch assembly See Section 5 even if the monitor switch operates normally The monitor fuse and monitor switch assembly is comprised of a 20 ampere fuse and switch 5 Reconnect all leads removed from components during testing 6 Reassemble the unit 7 Reconnect the power supply cord 8 Run the oven and check all functions M POWER TRANSFORMER T...

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