Component Removal - Drawer Microwave

COMPONENT ACCESS AND REMOVAL

This section explains how to adjust, access, and remove components in a Drawer Microwave Oven. Procedures are arranged to simulate the order in which components would typically need to be removed to gain access to others. Referencing other component removal procedures may be necessary.

NOTE: Before continuing, please review the WARNINGS and CAUTION below.

▲ WARNING

HIGH VOLTAGE: MICROWAVE OVENS CONTAIN CIRCUITRY CAPABLE OF PRODUCING VERY HIGH VOLTAGE AND CURRENT. CONTACT WITH THE FOLLOWING COMPONENTS MAY RESULT IN SERIOUS PERSONAL INJURY OR DEATH:

• TRANSFORMER
• CAPACITOR
• RECTIFIER
• MAGNETRON
• HIGH VOLTAGE HARNESS

• BEFORE SERVICING MICROWAVE OVEN, THE CAPACITOR MUST BE DISCHARGED BY SHORTING THE CONNECTING LEAD OF THE RECTIFIER AGAINST THE CHASSIS WITH AN INSULATED SCREWDRIVER. FAILURE TO FOLLOW THIS STEP COULD RESULT IN SERIOUS PERSONAL INJURY OR DEATH (SEE FIGURE 4-1 ON PAGE 4-3).
• TO AVOID ELECTRIC SHOCK, POWER TO UNIT MUST BE DISCONNECTED WHENEVER ACCESSING AND/OR REMOVING COMPONENTS POWERED BY ELECTRICITY OR COMPONENTS NEAR OTHER ELECTRICAL COMPONENTS.
• BEFORE WIRING:
  1. DISCONNECT POWER SUPPLY CORD, OPEN DRAWER, WAIT 60 SECONDS, THEN DISCHARGE THE HIGH VOLTAGE CAPACITOR.
  2. DON'T LET THE WIRE LEADS TOUCH TO THE FOLLOWING PARTS:
     • HIGH VOLTAGE PARTS: MAGNETRON, HIGH VOLTAGE TRANSFORMER, HIGH VOLTAGE CAPACITOR AND HIGH VOLTAGE RECTIFIER ASSEMBLY.
     • HOT PARTS: OVEN LAMP, MAGNETRON, HIGH VOLTAGE TRANSFORMER AND OVEN CAVITY.
• TO AVOID EXPOSURE TO MICROWAVES, NEVER OPERATE OR ALLOW DRAWER MICROWAVE TO BE OPERATED WITH THE DRAWER OPEN.
• AFTER PERFORMING ANY REPAIR TO THE DOOR, DRAWER LATCH MECHANISM, OR DRAWER CLOSING FACE, YOU MUST TEST THE INTEGRITY OF THE DRAWER SEAL WITH A MICROWAVE LEAK DETECTOR TO VERIFY THERE ARE NO MICROWAVE LEAKS. (SEE PROCEDURES ON PAGE 4-4)
• IF NECESSARY TO REMOVE MICROWAVE OVEN FROM ITS INSTALLATION, REMEMBER THAT THE UNIT IS HEAVY AND COULD TIP AND/OR FALL, RESULTING IN SERIOUS INJURY.

▲ CAUTION

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

NOTE: When all service work is completed and the oven is fully assembled, the microwave power output should be checked and a microwave leakage test should be performed and drawer interlock operation checked (See Following Page).

FIGURE 4-1. Discharge Capacitor

Diagram illustrating the discharge of a capacitor. It shows a capacitor, rectifier, red and white wires, and chassis. A screwdriver is shown shorting the connecting lead of the rectifier against the chassis. Text indicates that before servicing, the capacitor must be discharged by shorting the connecting lead of the rectifier against the chassis with an insulated screwdriver.

PRECAUTIONS FOR USING LEAD-FREE SOLDER

1. Employing Lead-Free Solder: The "Main PWB" of this model employs lead-free solder, indicated by the "LF" symbol on the PWB and in the service manual. The suffix letter denotes the alloy type of the solder (e.g., Sn-Ag-Cu for tin, silver, and copper).
2. Using Lead-Free Wire Solder: When repairing a PWB with the "LF" symbol, only lead-free solder should be used. Using normal tin/lead alloy solder may result in cold soldered joints and damage to printed patterns. As the melting point of lead-free solder is approximately 40°C higher than tin/lead alloy solder, it is recommended to use a dedicated bit and adjust the iron temperature accordingly.
3. Soldering: Due to the higher melting point and poorer wettability (flow) of lead-free solder (Sn-Ag-Cu), extreme care must be taken not to leave the soldering bit in contact with the PWB for an extended period to prevent damage to the land. Remove the bit as soon as good flow is achieved. The high tin content in lead-free solder can cause premature corrosion of the bit. To reduce wear on the bit, lower the temperature or turn off the iron when not required. Mixing solder types on the bit can cause contamination, altering alloy characteristics and making good soldering more difficult. Bits need to be cleaned and replaced more often when using lead-free solder. To reduce bit wear, clean the bit thoroughly after each use.

MICROWAVE MEASUREMENT PROCEDURE

1. Requirements:
   • Microwave leakage limit (Power density limit): The power density of microwave radiation emitted by a microwave oven should not exceed 5 mW/cm² at any point 5cm or more from the external surface of the oven, measured prior to purchase and throughout the oven's useful life.
   • Safety interlock switches: Primary interlock relay switch shall prevent microwave radiation emission exceeding the specified limit. Secondary interlock relay and door sensing switch shall prevent microwave radiation emission exceeding 5 mW/cm² at any point 5cm or more from the external surface of the oven.
2. Preparation for testing: Before beginning the actual measurement of leakage, proceed as follows:
   • Ensure the actual instrument is operating normally as specified in its instruction booklet.
   • NOTES: Survey instruments must comply with performance standards for microwave ovens (2 CFR 030.0(c)(3)(i)), CSA, and NHW standards. Recommended instruments include NARDA 800 and NARDA 8200.
   • Place a load of 275±5 ml (9.8 oz) of tap water, initially at 20±5°C (68°F), in the center of the oven cavity. Use a low-form, 600 ml (20 oz) beaker made of electrically non-conductive material (glass or plastic) with an inside diameter of approximately 8.5 cm (3½ in.). This standard load is important for protecting the oven and ensuring accurate leakage measurement.
   • Set the cooking control to Full Power Cooking Mode.
   • Close the drawer and select a cook cycle of several minutes. If the water begins to boil before the survey is completed, replace it with 275 ml of cool water.
3. Leakage test: Closed-drawer leakage test (microwave measurement):
   • Grasp the probe of the survey instrument and hold it perpendicular to the gap between the drawer and the body of the oven.
   • Move the probe slowly (not faster than 1 in./sec. or 2.5 cm/sec.) along the gap, observing the maximum indication on the meter.
   • Check for leakage at the drawer screen, sheet metal seams, and other accessible positions where metal continuity is breached (e.g., around switches, indicators, vents). While testing around the drawer, pull the drawer away from the front of the oven as far as permitted by the closed latch assembly.
   • Measure carefully at the point of highest leakage. Ensure the highest leakage is no greater than 4mW/cm², and that the primary interlock switch/secondary interlock relay turns the oven OFF before any drawer movement.

BEFORE OPERATING OVEN AFTER SERVICE

1. Disconnect the power supply cord.
2. Ensure a definite "click" is heard when the microwave oven drawer is unlatched. (Hold the drawer closed with one hand, then pull the drawer open. This causes the latch leads to rise, allowing a "click" as the drawer switches operate.)
3. Visually check the drawer and cavity face plate for damage (dents, cracks, signs of arcing, etc.).
4. Do not operate the oven if any of the following conditions exist:
   • Drawer does not close firmly.
   • Drawer latch hook is damaged.
   • Drawer gasket or seal is damaged.
   • Drawer is bent or warped.
   • Defective parts in the drawer interlock system.
   • Defective parts in the microwave generating and transmission assembly.
   • Visible damage to the oven.
5. Do not operate the oven: Without the RF gasket (Magnetron); if the waveguide or oven cavity are not intact; if the drawer is not closed.

TOUCH CONTROL PANEL SERVICING

1. Precautions for Handling Electronic Components: This unit uses CMOS LSI. CMOS LSI have extremely high impedance and are sensitive to surrounding high voltage power sources and static electricity. Handle with care, ensuring proper grounding. Wrap components in aluminum foil for storage and transport.
2. Servicing of Touch Control Panel: Procedures for servicing the touch control panel are described below, along with necessary precautions. Power to the touch control panel can be supplied either from the oven's power line or an external source.
   • Servicing with oven power supply: Before checking performance, disconnect the power supply cord, open and block the drawer open, discharge the high voltage capacitor (See Figure 4-1), disconnect leads to the primary power transformer, and insulate these leads. Reconnect the power supply cord. After checking performance, disconnect the power supply cord, reconnect transformer leads, open and block drawer, reinstall outer case, reconnect power supply cord, and run the oven to check all functions.
   • On some models, the power supply cord is short, requiring servicing while connected.
   • On other models, the power supply cord is longer, allowing separation. In this case, short both ends of the door sensing switch (on PWB) with a jumper to simulate a closed door. Use dummy resistors for sensor-related controls.
3. Servicing Touch Control Panel with Power Supply from an External Power Source: Disconnect the touch control panel from the oven. Short the door sensing switch (on PWB) with a jumper. Connect an external power source to the touch control panel's power input terminal. Use dummy resistors for sensor-related controls.
4. Servicing Tools:
   • Soldering iron: 30W (grounding terminal recommended).
   • Oscilloscope: Single beam, frequency range DC-0MHz or higher.
   • Others: Hand tools.

▲ WARNING

THE HIGH VOLTAGE TRANSFORMER OF MICROWAVE OVEN IS STILL LIVE DURING SERVICING AND PRESENTS A HAZARD.

• Disconnect the power supply cord, and then remove the outer case.
• Open the door and block it open.
• Discharge high voltage capacitor. (See Figure 4-1 on page 4-3)
• 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 tape.
• Re-connect the power supply cord.

After checking the performance of the touch control panel:

• Disconnect the power supply cord.
• Re-connect the leads to the primary of the power transformer.
• Open the door and block it open.
• Re-install the outer case (cabinet).
• Re-connect the power supply cord after the outer case is installed.
• Run the oven and check all functions.

On some models, the power supply cord between the touch control panel and the oven itself is so short that the two can't be separated. For those models, check and repair all controls (sensor-related ones included) of touch control panel while keeping it connected to the oven.

On some models, the power supply cord between touch control panel and oven proper is long enough that they may be separated from each other. For those models, it is possible to check and repair the controls of touch control panel while keeping it apart from oven proper; in this case you must short both ends of the door sensing switch (on PWB) of the touch control panel with a jumper, which activates an operational state that is equivalent to the oven door being closed. As for the sensor-related controls of the touch control panel, checking them is possible if dummy resistor(s) with resistance equal to that of the controls are used.

Servicing Touch Control Panel with Power Supply from an External Power Source: Disconnect touch control panel completely from the oven proper, and short both ends of the door sensing switch (on PWB) of the touch control panel, which activates an operational state that is equivalent to the oven door being closed. Connect an external power source to power input terminal of the touch control panel, then it is possible to check and repair the controls of the touch control panel. It is also possible to check the sensor-related controls of the touch control panel by using the dummy resistor(s).

DRAWER MICROWAVE DISASSEMBLY

WARNING: FOLLOW ALL SAFETY PRECAUTIONS AS STATED AT THE BEGINNING OF THIS SECTION BEFORE PROCEEDING!

1. Open the drawer and extract the four mounting screws holding the unit on to the wall or cabinet opening. (See Figure 4-2).
2. Close the drawer, then carefully pull the unit out from the opening and unplug the power supply cord. Place the unit on a sturdy work surface.
3. Extract four mounting screws (two on each side) from the left and right side angles to remove the louver vent from the unit (See Figure 4-3). Place vent off to the side, on a flat protected surface.
4. Remove the top cover. (See Figure 4-3).
5. Remove the air cover from the back of the unit, both right and left side angles, then both side cabinet panels (See Figure 4-3).
6. Remove the exhaust duct. Disconnect the ground wire terminal from the grounding peg on the back plate. Then, remove back plate (See Figure 4-3).
7. NOTE: You now have access to various components for the drawer.
8. To remove the control panel frame assembly from the top of the drawer, extract five mounting screws holding the control panel frame to the control panel angle in the back of the drawer (See Figure 4-4).
9. Unsnap the top control board assembly away from the control panel frame and unplug all wires. The control board assembly is now free.
10. If the control board is being replaced, transfer connectors one at a time to the new control board, to ensure proper connection.
11. NOTE: At this point, you will have access to all parts of the drawer microwave.

FIGURE 4-2. Installation Mounting Screw Removal

Diagram showing the removal of mounting screws for installation.

FIGURE 4-3. Drawer Microwave Exploded View

Diagram showing an exploded view of the drawer microwave, labeling parts like Lamp Access Panel, Left Side Angle, Louver Vent, Left Side Cabinet Panel, Cavity, Screws, Air Cover, Top Plate, Right Side Angle, Right Side Cabinet Panel, Exhaust Duct, and Back Plate.

FIGURE 4-4. Touch Control Panel Removal

Diagram illustrating the removal of the touch control panel.

Upper Cabinet Component Replacement: (Sensor, Stirrer Motor, Upper Thermal Limiter)

1. Drawer Microwave must be removed from its installation. See Drawer Microwave Disassembly (page 4-6) steps 1-3.
2. Wait 60 Sec. to discharge High Voltage Capacitor.
3. Using a phillips screwdriver, remove the two mounting screws (one on each side of the stirrer motor) that fasten the stirrer motor assembly to the top of the unit (See Figure 4-5).
4. NOTES:
   • The stirrer motor shaft has flat spots that must be aligned with the stirrer fan assembly for reinstallation.
   • Please see "After Servicing" (Page 4-11) when repair is complete.

Cavity Light Replacement:

1. Drawer Microwave must be removed from its installation. See Drawer Microwave Disassembly (page 4-6) steps 1-3.
2. Locate and remove lamp access panel in top plate (See Figure 4-3 on page 4-6).
3. NOTE: Lamp and socket are an assembly. You must change socket along with the lamp.
4. Remove lamp socket screw to remove the lamp assembly and replace with new (See Figure 4-6).

Power Cord Replacement:

1. Un-hook the black and white AC terminals from the noise filter PWB and green ground wire from the back plate (See Figure 4-7).
2. Attach the black and white AC terminals from the new power cord to the noise filter as shown in figure 4-7.
3. NOTE: The green ground wire terminal can be attached when reassembling the back plate to the drawer cavity.

FIGURE 4-5. Upper Components

Diagram showing upper components, including stirrer motor and screws.

FIGURE 4-6. Lamp & Socket Removal

Diagram illustrating the removal of the lamp and socket.

FIGURE 4-7. Power Cord Replacement

Diagram showing the power cord replacement process, including connections to the noise filter, black plate, and ground wire.

Stop Switch, Secondary Interlock Switch and Monitor Switch Removal:

1. Follow the Drawer Microwave disassembly as previously stated on page 4-6, steps 1-3.
2. Open the drawer and keep it open.
3. To discharge the high voltage capacitor, wait for 60 seconds.
4. Extract the mounting screw/washer holding the latch hook to the latch angle assembly (See Figure 4-8).
5. Remove the latch hook from the latch angle assembly.
6. Disconnect the wire leads of each switch.
7. Remove each switch from the latch hook by pushing the one stopper tab (located at the bottom) holding each switch (See Figure 4-8).
8. NOTE: Care must be taken not to break the plastic stopper tab or the holding clips.
9. Now, each switch is free.

Re-install:

1. Re-install each switch in its place. The secondary interlock switch is in the lower position and the monitor switch is in the top position, located on the left side of the unit. The door sensing switch is by itself on the right side of the unit.
2. Re-connect wire leads to each switch (See Figure 4-6).
3. Secure the latch hooks with mounting screws to oven flange.
4. Make sure that the monitor switch is operating properly and check continuity of the monitor circuit. Refer to section 5, Troubleshooting Guide "Test Procedure" pages 5-13 and 5-14 and "Adjustment procedure" on page 4-9.

FIGURE 4-8. Switch Assembly Removal (Door Sensing Switch Shown)

Diagram showing the removal of the switch assembly, including mounting screws, latch hook, latch angle assembly, oven flange, disconnect wires, switch, and stopper tab.

Stop Switch, Secondary Interlock Switch and Monitor Switch Adjustment:

1. Follow the Drawer Microwave disassembly as previously stated on page 4-6.
2. Open the drawer and keep it open.
3. To discharge the high voltage capacitor, wait for 60 seconds.
4. If the door sensing switch, secondary interlock switch and monitor switch do not operate properly due to a misadjustment, the following adjustment should be made.
5. Loosen the screw holding latch hook to the oven cavity flange.
6. With drawer closed, adjust latch hook by moving it back and forth, and up and down. In and out play of the door allowed by the upper and lower position of the latch hook should be less than 0.5mm. The vertical position of the latch hook should be adjusted so that the secondary interlock switch is activated with the drawer closed. The horizontal position of the latch hook should be adjusted so that the monitor switch and drawer sensing switch are activated with the drawer closed.
7. Secure the screws with washers firmly.
8. Check all of the switches operation. If any switch has not activated fully, you will need to adjust the slide rail attached to the microwave cavity.
9. This is done by following the steps to remove the "Drawer Assembly and Drawer Support Angle Removal" on page 4-10. After you have removed the drawer support covers, loosen the two screws holding the slide rail to the microwave cavity and tilt the front end up and the rear end down, then tighten the screws (See Figure 4-9).
10. Check and assure that the cap nuts on the drawer support angles are centered when passing through the cavity face plate.

After Adjustment, Check The Following:

1. In and out play of door remains less than 0.5mm when in the latched position. First check upper position of latch hook, pushing and pulling upper portion of drawer toward the oven face. Then check lower portion of the latch hook, pushing and pulling lower portion of the door toward the oven face. Both results (play in the door) should be less than 0.5mm.
2. The secondary interlock switch interrupts the circuit before the door can be opened.
3. Monitor switch contacts close when door is opened.
4. Door sensing switch contacts open when door is opened.
5. Reassemble the unit and check for microwave leakage around door with an approved microwave survey meter (Refer to Microwave Measurement Procedure on page 4-4).

FIGURE 4-9. Slide Rail Adjustment

Diagram showing slide rail adjustment, indicating loosening screws and adjusting the slide rail.

Drawer Assembly and Choke Cover Removal:

1. Follow the Drawer Microwave disassembly as previously stated on page 4-6.
2. Open the drawer and keep it open.
3. To discharge the high voltage capacitor, wait for 60 seconds.
4. Remove the both right and left side cabinet panels.
5. Remove the two drawer support covers from the choke cover as shown in Figure 4-10.
6. Insert a putty knife or flat thin blade screwdriver (thickness of about 0.5mm) into the gap between the choke cover and the door frame (See Figure 4-10).
7. Carefully slide choke cover away from drawer as far as possible.
8. Extract six mounting screws from all three drawer support angles as shown in Figure 4-11.
9. Unhook the drawer support angles from the drawer, then remove.
10. Now, the door assembly is free and the choke cover can now be removed.

Drawer Support Angle Removal:

1. Remove the drawer assembly and choke cover first.
2. Remove two mounting screws from the right or left latch angle assembly, then remove angle assembly (See Figure 4-12).
3. Separate slide rails by moving inside lever of slide rail. The slide rail will now separate by pulling straight forward and out (See Figure 4-13).
4. At this point, you can replace either latch angle assy or latch angles.
5. To reassemble, just reverse the above order.

FIGURE 4-10. Choke Cover Removal

Diagram showing choke cover removal, indicating drawer support angles, choke cover, and screws.

FIGURE 4-11. Drawer Support Screw Removal

Diagram showing drawer support screw removal, indicating screws and drawer support angles.

FIGURE 4-12. Latch Angle Assembly Removal

Diagram illustrating the removal of the latch angle assembly.

FIGURE 4-13. Disconnect Center Slides

Diagram showing how to disconnect center slides.

After Reassembly, Do The Following:

1. Make sure that drawer sensing switch, secondary interlock switch and monitor switch are operating properly. (Refer to section 5, Troubleshooting Guide "Test Procedures".)
2. An approved microwave survey meter should be used to assure compliance with proper microwave radiation emission limitation standards.

After Any Servicing, Make Sure Of The Following:

1. The drawer latch heads smoothly catch the latch hook through the latch holes and that the latch head goes through the center of the latch hole.
2. Deviation of door alignment from horizontal line of cavity face plate is to be less than 1.0mm.
3. Drawer is positioned with its face pressed toward cavity face plate.
4. Reassemble the unit and check for microwave leakage around the drawer with an approved microwave survey meter (Refer to Microwave Measurement Procedure).

NOTE: The drawer on a microwave oven is designed to act as an electronic seal preventing the leakage of microwave energy from oven cavity during cook cycle. This function does not require that door be air-tight, moisture (condensation)-tight or light-tight. Therefore, occasional appearance of moisture, light or sensing of gentle warm air movement around oven drawer is not abnormal and do not of themselves.

Actuator Removal:

1. Follow the Drawer Microwave disassembly as previously stated on page 4-6.
2. Open the drawer and keep it open.
3. To discharge the high voltage capacitor, wait for 60 seconds.
4. Locate either the right or left actuator and remove the two mounting screws holding the actuator to the door support angles (See Figure 4-14).
5. Replace with the new actuator.

Actuator Adjustment:

1. It is very critical that proper adjustment is made to actuator.
2. Adjust each actuator to fully depress ("0" gap) switch lever switches on left and right side (See Figure 4-14).
3. NOTE: If this adjustment is not adjusted correctly, it will effect the performance of the Auto Drawer.

FIGURE 4-14. Actuator Removal/ Adjustment

Diagram showing actuator removal and adjustment, indicating screws, door support angle, actuator, and "0" gap.

Auto Drawer Gear Removal/Installation:

NOTES:

• This procedure requires a 14" or greater phillips screwdriver.
• The MWD30-2 auto drawer gear can be pulled straight out, after removing screws holding gear to cavity.

1. Disengage any power going to the unit.
2. Open the drawer and keep it open.
3. Remove the top cover and right side cabinet.
4. Unhook wiring to auto drawer gear.
5. Remove the bottom screw from below the auto drawer gear (See Figure 4-15).
6. Extract four (4) mounting screws holding the auto drawer gear to the bottom cavity angle (See Figure 4-16).
7. Disengage (pull) the auto drawer gear from rack gear and slide to the right (toward the rear), then turn motor 90° and slip out along the rear of the drawer.
8. Then tilt auto gear motor 20° to remove the assembly. The auto drawer gear is now free.

Installation:

1. Proceed in reverse to reinstall the auto drawer gear taking care that the gear teeth are set into the cavity angle correctly.

FIGURE 4-15. Auto Drawer Gear Screw Removal

Diagram showing auto drawer gear screw removal, indicating bottom of unit and screws.

FIGURE 4-16. Auto Drawer Gear Mounting Screws

Diagram showing auto drawer gear mounting screws.

Rack Gear Removal:

1. Follow the Drawer Microwave disassembly as previously stated on page 4-6.
2. Open the drawer and keep it open.
3. To discharge the high voltage capacitor, wait for 60 seconds.
4. Remove the drawer microwave by following step 1, 2, 5, 8, 9 & 10 as instructed under "Drawer Assembly and Choke Removal".
5. Remove the three (3) mounting screws holding the rack gear to the bottom slide rail (See Figure 4-17).
6. Proceed in reverse to reinstall the new rack gear.

FIGURE 4-17. Rack Gear Removal

Diagram showing rack gear removal, indicating bottom drawer support, screws, rack gear, and bottom view of unit.

Major Control Components:

1. Drawer Microwave must be removed from its installation. Remove the top plate, both side cabinet panels, the exhaust duct and the back plate.
2. Only attempt to remove a major control component after allowing the capacitor to self discharge which takes approximately 60 seconds, or discharge capacitor as instructed on page 4-3.
3. All major control components are attached with phillips head screws. To Remove a component, extract its mounting screws after detaching electrical wiring.
4. NOTE: Be careful to maintain proper wire location. Check for clear wire marking before removing any wires and label any wires that can not be easily identified.

Drawer Microwave Major Control Components

Diagram showing major control components of the drawer microwave, including Thermal Cut-Out, HV Capacitor, HV Transformer, Magnetron, Fan Motor, Power Supply, Monitor Fuse, and wiring connections.