MICROWAVE OVEN
SERVICE MANUAL
MODEL : MB-394A, MH-594A
CAUTION
BEFORE SERVICING THE UNIT, READ THE
SAFETY PRECAUTIONS IN THIS MANUAL.
SERVICE INFORMATION
TOOLS AND MEASURING INSTRUMENTS
NECESSARY TOOLS
Tools normally used for TV servicing are sufficient. Standard tools are listed below.
¥Diagonal pliers
¥Long nose pliers
¥Phillips screwdriver
¥Flat blade screwdriver
¥Wrench (size 5mm)
¥Nutdriver (size 5mm)
¥Adjustable wrench
¥Soldering iron
¥Solder
¥Vinyl insulation tape
¥Polishing cloth
NECESSARY MEASURING INSTRUMENTS
¥TESTER(VOLTS-DC, AC., Ohmmeter)
¥Microwave survey meter
-Holaday HI-1500
HI-1501 - Narda 8100
8200
¥Inch scale
¥600 cc non conductive material beaker (glass or plastic),
inside diameter: approx. 8.5 cm(31/2 in.)
¥Cylindrical and made of borosilicate glass vessel. max. thickness: 3 mm
outside diameter: approx. 190mm height: approx. 90mm
¥Glass thermometer: 100¡C or 212¡F (1 deg scale)
MICROWAVE LEAKAGE TEST
CAUTIONS
¥Be sure to check microwave leakage prior to servicing the oven if the oven is operative prior to servicing.
¥The service personnel should inform the manufacture importer, or assembler of any certified oven unit found to have a microwave emission level in excess of 5 mW/cm2 and should repair any unit found to have excessive emission levels at no cost to the owner and should ascertain the cause of the excessive leakage. The service personnel should instruct the owner not to use the unit until the oven has been brought into compliance.
¥If the oven operates with the door open, the service personnel should:
-Tell the user not to operate the oven.
-Contact the manufacturer.
¥The service personnel should check all surface and vent openings for microwave leakage.
¥Check for microwave leakage after every servicing. The power density of the microwave radiation leakage emitted by the microwave oven should not exceed
4 mW/cm2. Always start measuring of an unknown field to assure safety for operating personnel from radiation leakage.
MEASURING MICROWAVE ENERGY LEAKAGE
¥Pour 275±15cc of 20±5¡C(68±9¡F) water in a beaker which is graduated to 600 cc, and place the beaker on the center of the turntable.
¥Set the energy leakage monitor to 2,450 MHz and use it following the manufacturer's recommended test procedure to assure correct result.
¥When measuring the leakage, always use the 2- inch (5cm) spacer supplied with the probe.
¥Operate the oven at its maximum output.
¥Measure the microwave radiation using and electromagnetic radiation monitor by holding the probe perpendicular to the surface being measured
Move probe along shaded area
Probe scanning speed Less than 2.5 cm/sec ( 1in/sec)
5-1
MEASUREMENT WITH OUTER CASE REMOVED
¥When you replace the magnetron, measure for microwave energy leakage before the outer case is installed and after all necessary components are replaced or adjusted.
Special care should be taken in measuring the following parts. (Circled area of below Fig.)
-Around the magnetron
-The waveguide
WARNING : AVOID CONTACTING ANY
HIGH VOLTAGE PARTS
(Magnetron, H.V. Transformer,
H.V. Capacitor, H.V. Cable AssÕy,
H.V. Circuit Protector)
MEASUREMENT WITH A FULLY ASSEMBLED OVEN
¥After all components, including the outer case, are fully assembled, measure for microwave energy leakage around the door viewing window, the exhaust opening, and air inlet openings.
¥Microwave energy leakage must not exceed the values prescribed below.
NOTE: Leakage with the outer case removedless than 5 mW/cm.sq. Leakage for a fully assembled oven (Before the latch switch (primary) is interrupted) with the door in a slightly opened position-less than 2 mW/cm.sq.
NOTES WHEN MEASURING
¥Do not exceed meter full scale deflection.
¥The test probe must be removed no faster than 1 inch/sec (2.5 cm/sec) along the shaded area, otherwise a false reading may result.
¥The test probe must be held with the grip portion of the handle.
A false reading may result if the operator's hand is between the handle and the probe.
¥When testing near a corner of the door, keep the probe perpendicular to the surface making sure the probe horizontally along the oven surface, this may possibly cause probe damage.
RECORD KEEPING AND NOTIFICATION AFTER MEASUREMENT
¥After adjustment and repair of any microwave energy interruption or microwave energy blocking device, record the measured values for future reference. Also enter the information on the service invoice.
¥The microwave energy leakage should not be more than 4 mW/cm.sq. after determining that all parts are in good condition, functioning properly and genuine replacement parts which are listed in this manual have been used.
¥At least once a year, have the electromagnetic energy leakage monitor checked for calibration by its manufacturer.
5-2
MEASUREMENT OF MICROWAVE POWER OUTPUT
¥Microwave power output measurement is made with the microwave oven supplied at its rated voltage and operated at its maximum microwave power setting with a load of (1000±5) g of potable water.
¥The water is contained in a cylindrical borosilicate glass vessel having a maximum material thickness of 3 mm and an outside diameter of approximately 190mm.
¥The oven and the empty vessel are at ambient temperature prior to the start of the test.
¥The initial temperature (T1) of the water is (10±2)¡C It is measured immediately before the water is added to the vessel. After addition of the water to the vessel, the load is immediately placed on the center of the turntable which is in the lowest position and the microwave power switched on.
¥The time T for the temperature of the water to rise by a value Æ T of (10±2)¡K is measured, where T is the time in seconds and ÆT is the temperature rise. The initial and final water temperatures are selected so that the maximum difference between the final water temperature and the ambient temperature is 5¡K.
¥The microwave power output P in watts is calculated from the following formula :
4187 X ( T) + 0.88 X (T2 - T0) X M
P =
T
¥T2: Temperature after heating
¥T0: Temperature after bowl
¥M: Weight of bowl
is measured while the microwave generator is operating at full power. Magnetron filament heat-up time is not included. (about 3 sec)
¥The water is stirred to equalize temperature throughout the vessel, prior to measuring the final water temperature.
¥Stirring devices and measuring instruments are selected in order to minimize addition or removal of heat.
WATER LOAD
TURNTABLE
DISASSEMBLY AND ADJUSTMENT
A. OUTER CASE REMOVAL
1)Disconnect the power supply cord from the outlet.
2)Remove the screws from the rear and along side edges of the case.
The outer case must be moved backward to be lifted off.
C. CONTROL PANEL ASSEMBLY
1)Disconnect the leadwire from the PCB SUB ASSÕY.
2)Remove the screws for the earth and securing the control panel.
3)Lift control panel ASSÕY from the oven by the tab unhooked.
B. POWER SUPPLY CORD
1)Remove the outer case.
2)Disconnect two terminals, and remove one screw of the earth terminal.
CAUTION: DISCHARGE THE HIGH VOLTAGE CAPACITOR BEFORE SERVICING
(refer to page 2-1)
5-3
D. DOOR GROSS ASSEMBLY REMOVAL
1)Open the door.
2)Remove the choke cover cap very carefully with a flat-blade screwdriver.
CAUTION : Be careful not to damage door seal plate by screwdriver.
3) Lift up and push the door.
NOTE:
1.After replacing the door, be sure to check that the primary switch, monitor switch, and secondary switch operate normally.
2.After replacing the door, check for microwave energy leakage with a survey meter. Microwave energy must be below the limit of 5 mW/cm. (with a 275 ml water load)
3.When mounting the door assembly to the oven assembly, be sure to adjust the door assembly parallel to the chassis. Also adjust so the door has no play between the inner door surface and oven frame assembly. If the door assembly is not mounted properly, microwaves may leak from the clearance between the door and the oven.
Remove choke cover cap
Remove door |
Door seal plate |
E. HIGH VOLTAGE TRANSFORMER REMOVAL
1)Discharge the high voltage capacitor.
2)Disconnect the leadwire from magnetron, high voltage transformer, and capacitor.
3)Remove the screw holding the high voltage transformer to the baseplate.
F. FAN MOTOR ASSEMBLY REMOVAL
1)Discharge the high voltage capacitor.
2)Disconnect the leadwire from fan motor, noise filter and high voltage capacitor.
3)Remove the two screws holding the the suction guide ASSÕY to the oven cavity and remove the high voltage diode earth screw.
4)Remove the screw of the capacitor bracket.
5)Remove the two screws holding the fan motor ASSÕY to the suction guide ASSÕY.
G. HIGH VOLTAGE CAPACITOR AND DIODE REMOVAL
1)Discharge the high voltage capacitor.
2)Disconnect the leadwire from fan motor, noise filter and high voltage capacitor.
3)Remove the screw holding the suction guide ASSÕY to the oven cavity and remove the high voltage diode earth screw.
Remove the screw holding the high voltage capacitor bracket.
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Fan Motor ASS'Y |
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Suction |
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Guide |
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H.V. |
H.V. |
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Transformer |
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Capacitor |
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H.V. |
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Diode |
5-4
H. AIR DUCT ASSEMBLY REMOVAL
1)Disconnect the leadwire from lamp.
2)Remove the mounting screw to Latch Board.
I. MAGNETRON REMOVAL
1)Disconnect the leadwire from the high voltage transformer and high voltage capacitor.
2)Carefully remove the mounting screws holding the magnetron and the waveguide.
3)Remove the magnetron ASSÕY until the tube is clear from the waveguide.
NOTE:
1.When removing the magnetron, make sure its dome does not hit any adjacent parts, or it may be damaged.
2.When replacing the magnetron, be sure to install the magnetron gasket in the correct position and be sure that the gasket is in good condition.
3.After replacing the magnetron, check for microwave leakage with a survey meter around the magnetron. Microwave energy must be below the
limit of 5 mW/cm2. (With a 275 ml. water load).
Make sure that gasket is rigidly attached to the magnetron. To prevent microwave leakage, tighten the mounting screws properly, making sure there is no gap between the waveguide and the
Magnetron |
Waveguide |
Dome |
Waveguide |
Bracket |
Magnetron |
Gasket |
Magnetron |
J. REMOVING THE TURNTABLE MOTOR
1)Remove the turntable.
2)Remove the Rotating Ring.
3)Lay the unit down on its back.
4)Remove the turntable motor cover.
The turntable base cover is easily removed by pinching the six parts with a wire cutting.
5)Disconnect the leadwire from the turntable motor terminals.
6)Remove the screw securing the turntable motor to the oven cavity ASSÕY
7)After repairing the motor, rotate the removed turntable motor cover.
8)Fit the turntable motor coverÕs projecting part to the base plate slit.
NOTE:
1.Remove the wire lead from the turntable motor VERY CAREFULLY.
2.Be sure to grasp the connector, not the wires, when removing.
Wire Leads |
Turntable Motor |
5-5
K. PCB ASSEMBLY REMOVAL
1)Remove the control panel assembly from the cavity. (Refer to control panel assembly removal on previous page.)
2)Remove screws which hold the PCB SUB ASSÕY to the control panel.
3)Disconnect the flat cable from the PCB SUB ASSÕY and take off the PCB SUB ASSÕY.
Control Panel |
PCB Sub ASS'Y |
Key Membrane |
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L. INTERLOCK SYSTEM
1) INTERLOCK MECHANISM
The door lock mechanism is a device which has been specially designed to eliminate completely microwave activity when the door is opened during cooking and thus to prevent the danger resulting from the microwave leakage.
2)MOUNTING OF THE PRIMARY/MONITOR/ SECONDARY SWITCHES TO THE LATCH BOARD
ADJUSTMENT
DIRECTION
PRIMARY
SWITCH
MONITOR
SWITCH
SECONDARY
SWITCH
3)INSTALLATION AND ADJUSTMENT OF THE LATCH BOARD TO THE OVEN ASSEMBLY
¥Mount the latch board to the oven assembly.
¥Adjust the latch board in the arrow direction so that oven door will not have any play in it when the door is closed.
¥Tighten the mounting screw.
¥Check for play in the door by pushing the door release button. Door movement should be less than 0.5 mm. (1/64 inch)
Don't push the door release button while making adjustment. Make sure that the latch moves smoothly after adjustment are completed and that the screws are tight. Make sure the primary, monitor, and secondary switches operate properly by following the continuity test procedure.
FIG. 1 |
CAUTION: CHECK THE CORRECT POSITION |
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MAGNETRON |
H.V. TRANSFORMER
H.V.
DIODE
H.V. CAPACITOR
PRIMARY |
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CIRCUIT PROTECTOR |
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5-6
INTERLOCK CONTINUITY TEST
WARNING : FOR CONTINUED PROTECTION AGAINST EXCESSIVE RADIATION EMISSION, REPLACE ONLY WITH IDENTICAL REPLACEMENT PARTS.
TYPE NO. SZM-V 16-FA-63 OR VP-533A-OF FOR PRIMARY SWITCH
TYPE NO. SZM-V 16-FA-62 OR VP-532A-OF FOR MONITOR SWITCH
TYPE NO. SZM-V 16-FA-63 OR VP-533A-OF FOR SECONDARY SWITCH
A. PRIMARY INTERLOCK SWITCH TEST
When the door release button is depressed slowly with the door closed, an audible click should be heard at the same time or successively at intervals. When the button is released slowly, the latches should activate the switches with an audible click.
If the latches do not activate the switches when the door is closed, the switches should be a adjusted in accordance with the adjustment procedure. Disconnect the wire lead from the primary switch. Connect the ohmmeter leads to the common (COM) and normally open (NO) terminal of the switch. The meter should indicate an open circuit in the door open condition. When the door is closed, the meter should indicate a closed circuit.
When the primary switch operation is abnormal, make the necessary adjustment or replace the switch only with the same type of switch.
B. SECONDARY INTERLOCK SWITCH TEST
Disconnect the wire lead from the secondary switch.
Connect the ohmmeter leads to the common (COM) and normally open (NO) terminals of the switch. The meter should indicate a open circuit in the door open condition. When the door is closed, meter should indicate an closed circuit. When the secondary switch operation is abnormal, make the necessary adjustment or replace the switch only with the same type of switch.
C. MONITOR SWITCH TEST
Disconnect the wire lead from the monitor switch. Connect the ohmmeter leads to the common (COM) and normally closed (NC) terminals of the switch. The meter should indicate closed circuit in the door open condition. When the door is closed, meter should indicate an open circuit. When the monitor switch operation is abnormal, replace with the same type of switch.
NOTE: After repairing the door or the interlock system, it is necessary to do this continuity test before operating the oven.
COMPONENTS |
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TEST PROCEDURE |
RESULTS |
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SWITCHES |
Check for continuity of the |
Door |
Door |
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(Wire leads removed) |
switch with an Ohm-meter |
open |
closed |
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Primary |
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Switch |
NO |
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COM |
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Monitor |
NC |
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Switch |
COM |
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Secondary |
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Switch |
NO |
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COM |
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NOTE : After checking for the continuity of switches, make sure that are |
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connected correctly. |
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5-7
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