Sharp MICROWAVE OVEN SX612R3C59PJ (R-3C590) Troubleshooting
Part-1 + Part 2
Never operate the oven until the following points are ensured.
(A) The door is tightly closed.
(B) The door brackets and hinges are not defective.
(C) The door packing is not damaged.
(D) The door is not deformed or warped.
(E) There is not any other visible damage with the oven.
Servicing and repair work must be carried out only by trained service engineers.
All the parts marked "*" on parts list are used at voltages more than 250V.
Removal of the outer wrap gives access to potentials above 250V.
All the parts marked "∆" on parts list may cause undue microwave exposure, by themselves, or when they are damaged, loosened or removed.
THE
WIRES IN THIS MAINS LEAD ARE COLORED IN ACCORDANCE WITH THE FOLLOWING CODE
GREEN
& YELLOW: EARTH
BLUE : NEUTRAL
BROWN : LIVE
BLUE : NEUTRAL
BROWN : LIVE
APPEARANCE
VIEW
Touch
control panel
OPERATION SEQUENCE
OFF CONDITION
Closing the door activates all door interlock switches (1st. latch switch, 2nd. latch switch and stop switch).
IMPORTANT
When the oven door is closed, the monitor switch contacts (COM-NC) must be open.
When the microwave oven is plugged in a wall outlet, rated voltage is supplied to the point A3+A5 in the control unit.
1. The display shows SHARP , MICRO-WAVE and OVEN .
2. To set any programmes or set the clock, you must first touch the STOP/CLEAR pad.
3. [ : ]appears in the display.
NOTE: When the oven door is opened, the oven lamp comes on at this time.
HIGH
COOKING
Enter a desired cooking time with the touching NUMBER pad and start the oven with touching START pad.
Enter a desired cooking time with the touching NUMBER pad and start the oven with touching START pad.
CONNECTED
COMPONENTS RELAY
Oven lamp, Fan motor, Turntable motor RY1
Power transformer RY2
Oven lamp, Fan motor, Turntable motor RY1
Power transformer RY2
1. Rated
voltage is supplied to the primary winding of the power transformer. The
voltage is converted to about 3.3 volts A.C. output on the filament winding and
high voltage of approximately 2000 volts A.C. on the secondary winding.
2. The filament winding voltage (3.3 volts) heats the magnetron filament and the high voltage (2000 volts) is sent to the voltage doubling circuit, where it is doubled to negative voltage of approximately 4000 volts D.C.
3. The 2450 MHz microwave energy produced in the magnetron generates a wave length of 12.24 cm. This energy is channeled through the waveguide (transport channel) into the oven cavity, where the food is placed to be cooked.
4. When the cooking time is up, a signal tone is heard and the relays RY1+RY2 go back to their home position. The circuits to the oven lamp, power transformer, fan motor and turntable motor are cut off.
5. When the door is opened during a cook cycle, the switches come to the following condition.
2. The filament winding voltage (3.3 volts) heats the magnetron filament and the high voltage (2000 volts) is sent to the voltage doubling circuit, where it is doubled to negative voltage of approximately 4000 volts D.C.
3. The 2450 MHz microwave energy produced in the magnetron generates a wave length of 12.24 cm. This energy is channeled through the waveguide (transport channel) into the oven cavity, where the food is placed to be cooked.
4. When the cooking time is up, a signal tone is heard and the relays RY1+RY2 go back to their home position. The circuits to the oven lamp, power transformer, fan motor and turntable motor are cut off.
5. When the door is opened during a cook cycle, the switches come to the following condition.
The
circuits to the power transformer, fan motor and turntable motor are cut
off when the 1st. latch switch, 2nd. Latch switch, and stop switch are
made open. The oven lamp remains on even if the oven door is opened
after the cooking cycle has been interrupted, because the relay RY1
stays closed. Shown in the display is the remaining time.
MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by oven door, and monitors the operation of the 1st and 2nd. Latch switches.
1.
When the oven door is opened during or after the cycle of a cooking
program, the 1st. latch switch, 2nd. Latch switch and stop switch must
open their contacts first. After that the contacts (COM-NC) of the
monitor switch can be closed.
2.
When the oven door is closed, the contacts (COMNC) of the monitor switch
must be opened. After that the contacts of the 1st. latch switch, 2nd.
latch switch and stop switch are closed.
3.
When the oven door is opened and the contacts of the-1st. latch switch,
2nd. latch switch remain closed. The fuse M8A will blow, because the
monitor switch is closed and a short circuit is caused.
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW COOKING
When
the microwave oven is preset for variable cooking power, 230-240 volts
A.C. power is supplied to the power transformer intermittently within a
32-second time base through the relay contact which is coupled with the
current-limiting relay. The following levels of microwave power are
given.
NOTE:
The ON/OFF time ratio does not exactly correspond to the percentage of
microwave power, because approx. 2 seconds are needed for heating up the
magnetron filament.
FUNCTION OF IMPORTANT COMPONENTS
DOOR OPEN MECHANISM
The
door is opened by pushing the open button on the control panel, refer to
the Figure D-1. When the open button is pushed, the open button
pushes up
the switch lever, and then the switch lever pushes up the the latch
head. The latch heads are moved upward and released from latch hook. Now
the door will open.
1ST.
LATCH SWITCH, 2ND. LATCH SWITCH AND STOP SWITCH
1. When the oven door is closed, the contacts COM-NO) must be closed.
2. When the oven door is opened, the contacts .(COMNO) must be opened.
MONITOR SWITCH
1. When the oven door is closed, the contacts (COM-NC) must be opened.
2. When the oven door is opened, the contacts (COMNC) must be closed.
3. If the oven door is opened and the contacts (COM-NO) of the 1st. latch switch and 2nd. latch switch fail to open, the fuse M8A blows simultaneously with closing the contacts (COM-NC) of the monitor switch.
CAUTION: BEFORE REPLACING A BLOWN FUSE M8A TEST THE 1ST. LATCH SWITCH, 2ND. LATCH SWITCH MONITOR SWITCH AND MONITOR RESISTOR FOR PROPER OPERATION.
1. When the oven door is closed, the contacts COM-NO) must be closed.
2. When the oven door is opened, the contacts .(COMNO) must be opened.
MONITOR SWITCH
1. When the oven door is closed, the contacts (COM-NC) must be opened.
2. When the oven door is opened, the contacts (COMNC) must be closed.
3. If the oven door is opened and the contacts (COM-NO) of the 1st. latch switch and 2nd. latch switch fail to open, the fuse M8A blows simultaneously with closing the contacts (COM-NC) of the monitor switch.
CAUTION: BEFORE REPLACING A BLOWN FUSE M8A TEST THE 1ST. LATCH SWITCH, 2ND. LATCH SWITCH MONITOR SWITCH AND MONITOR RESISTOR FOR PROPER OPERATION.
MONITOR
RESISTOR R 0.8Ω 20W
The monitor resistor prevents the fuse M8A bursting when the fuse M8A blows due to the operation of the monitor switch.
ASYMMETRIC RECTIFIER
The asymmetric rectifier is a solid state device that prevents current flow in both directions. And it prevents the temperature rise of the power transformer by blowing the fuse M8A when the high voltage rectifier is shorted.
The monitor resistor prevents the fuse M8A bursting when the fuse M8A blows due to the operation of the monitor switch.
ASYMMETRIC RECTIFIER
The asymmetric rectifier is a solid state device that prevents current flow in both directions. And it prevents the temperature rise of the power transformer by blowing the fuse M8A when the high voltage rectifier is shorted.
The
rated peak reverse voltage of D1 of the asymmetric rectifier is 6 KV The rated
peak reverse voltage of D2 of the asymmetric rectifier is 1.7 KV. D1 and D2 of
the asymmetric rectifier or high voltage rectifier are shorted when the each
peak reverse voltage goes beyond the each rated peak reverse voltage. (The
process of blowing the fuse M8A.)
1. The high voltage rectifier is shorted by any causes when microwave cooking.
2. The peak reverse voltage of D2 of the rectifier goes beyond the rated peak reverse voltage 1.7 KV in the voltage doubler circuit.
3. D2 of the rectifier is shorted.
4. The large electric currents flow through the high voltage winding of the power transformer.
5. The large electric currents beyond 8A flow through the primary winding of the power transformer.
6. The fuse M8A blows by the large electric currents.
7. The power supply to all the electrical parts is cut off
1. The high voltage rectifier is shorted by any causes when microwave cooking.
2. The peak reverse voltage of D2 of the rectifier goes beyond the rated peak reverse voltage 1.7 KV in the voltage doubler circuit.
3. D2 of the rectifier is shorted.
4. The large electric currents flow through the high voltage winding of the power transformer.
5. The large electric currents beyond 8A flow through the primary winding of the power transformer.
6. The fuse M8A blows by the large electric currents.
7. The power supply to all the electrical parts is cut off
FUSE
M8A
1. The fuse M8A blows when the contacts (COM-NO) of the 1st. latch switch and 2nd. latch switch remain closed with the oven door open and when the monitor switch closes.
2. The fuse M8A also blows when asymmetric rectifier, H.V. rectifier, H.V. wire harness, H.V.capacitor, magnetron or secondary winding of power transformer is shorted.
3. If the wire harness or electrical components are short-circuited, this fuse M8A blows to prevent an electric shock or fire hazard.
OVEN THERMAL CUT-OUT
The thermal cut-out, located on the top of the oven cavity, is designed to prevent damage to the oven by fire. If the foods load is overcooked, by either error in cook time or defect in the control unit, the thermal cut-out will open. Under normal operation, the oven thermal cut-out remains closed. However, when abnormally high temperatures are reached within the oven cavity, the oven thermal cut-out will open at 125˚C, causing the oven to shut down. The defective thermal cut-out must be replaced with new one.
1. The fuse M8A blows when the contacts (COM-NO) of the 1st. latch switch and 2nd. latch switch remain closed with the oven door open and when the monitor switch closes.
2. The fuse M8A also blows when asymmetric rectifier, H.V. rectifier, H.V. wire harness, H.V.capacitor, magnetron or secondary winding of power transformer is shorted.
3. If the wire harness or electrical components are short-circuited, this fuse M8A blows to prevent an electric shock or fire hazard.
OVEN THERMAL CUT-OUT
The thermal cut-out, located on the top of the oven cavity, is designed to prevent damage to the oven by fire. If the foods load is overcooked, by either error in cook time or defect in the control unit, the thermal cut-out will open. Under normal operation, the oven thermal cut-out remains closed. However, when abnormally high temperatures are reached within the oven cavity, the oven thermal cut-out will open at 125˚C, causing the oven to shut down. The defective thermal cut-out must be replaced with new one.
MAGNETRON
THERMAL CUT-OUT
The thermal cut-out located near the magnetron is designed to prevent damage to the magnetron if an over heated condition develops in the tube due to cooling fan failure, obstructed air guide, dirty or blocked air intake, etc. Under normal operation, the thermal cut-out remains closed. However, when abnormally high temperatures are reached within the magnetron, the thermal cut-out will open at 95˚C causing the oven to shut down, when the magnetron has cooled to 75˚C, the thermal cut-out closes and cook cycle will resume.
TURNTABLE MOTOR
The turntable motor drives the turntable roller assembly to rotate the turntable.
The thermal cut-out located near the magnetron is designed to prevent damage to the magnetron if an over heated condition develops in the tube due to cooling fan failure, obstructed air guide, dirty or blocked air intake, etc. Under normal operation, the thermal cut-out remains closed. However, when abnormally high temperatures are reached within the magnetron, the thermal cut-out will open at 95˚C causing the oven to shut down, when the magnetron has cooled to 75˚C, the thermal cut-out closes and cook cycle will resume.
TURNTABLE MOTOR
The turntable motor drives the turntable roller assembly to rotate the turntable.
The fan motor drives a blade which draws external cool air. This cool air is directed through the air vanes surrounding the magnetron and cools the magnetron. This air is channeled through the oven cavity to remove steam and vapors given off from the heating foods. It is then exhausted through the exhausting air vents at the oven cavity
NOISE FILTER
The noise filter prevents the radio frequency interference that might flow back in the power circuit.
Microwave oven - Sharp R3C590 - Troubleshooting
- Part-2
WARNING
TO SERVICE
TO
CHECK 3D
1) Disconnect
the supply.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.
3) Discharge high voltage capacitor.
AGAINST
THE CHARGE OF THE HIGH-VOLTAGE CAPACITOR
The
high-voltage capacitor remains charged about 60 seconds after the oven has been
switched off. Wait for 60 seconds and
then short-circuit the
connection of the high-voltage capacitor (that is, of the connecting lead of the high-voltage rectifier) against the chassis with the use of an insulated screwdriver.
connection of the high-voltage capacitor (that is, of the connecting lead of the high-voltage rectifier) against the chassis with the use of an insulated screwdriver.
Wherever
possible fault-finding is carried out with the supply disconnected. It may in,
some cases, be necessary to connect the supply after the outer case has been
removed, in this event carry out 3D checks and then disconnect the leads to the
primary of the power transformer. Ensure that these leads remain isolated from
other components and the oven chassis. (Use insulation tape if necessary.) When
the testing is completed carry out 3D checks and reconnect the leads to the primary of the power transformer.
When
all service work is completed, and the oven is fully assembled, the microwave
power output should be checked and microwave leakage test carried out.
TO
CHECK 4R
1) Reconnect all leads removed from components during testing.
2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run the oven. Check all functions.
Microwave ovens should not be run empty. To test for the presence of microwave energy within a cavity, place a cup of cold water on the oven turntable, close the door and set the microwave timer for two (2) minutes. Set the power level to HIGH and push the START button. When the two minutes has elapsed (timer at zero) carefully check that the water is now hot. If the water remains cold carry out 3D checks and reexamine the connections to the component being tested.
1) Reconnect all leads removed from components during testing.
2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run the oven. Check all functions.
Microwave ovens should not be run empty. To test for the presence of microwave energy within a cavity, place a cup of cold water on the oven turntable, close the door and set the microwave timer for two (2) minutes. Set the power level to HIGH and push the START button. When the two minutes has elapsed (timer at zero) carefully check that the water is now hot. If the water remains cold carry out 3D checks and reexamine the connections to the component being tested.
TROUBLESHOOTING
When
troubleshooting the microwave oven, it is helpful to follow the Sequence
of Operation in performing the checks. Many of the possible causes of
trouble will require that a specific test be performed. These tests are
given a procedure letter which will be found in the "Test Procedure".
IMPORTANT:
If the oven becomes inoperative because of a blown fuse M8A in the 1st.
latch switch - 2nd. latch switch - monitor switch - monitor resistor
circuit, check the 1st. latch switch, 2nd. latch switch, monitor switch
and monitor resistor before replacing the fuse M8A.
Click on the pictures to Zoom In
MAGNETRON
TEST
NEVER
TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL WHILE THE
OVEN IS IN OPERATION
CARRY
OUT 3D CHECK.
Isolate the magnetron from high voltage circuit by removing all leads connected to filament terminal. To test for an open circuit filament use an ohmmeter to make a continuity test between the magnetron filament terminals, the meter should show a reading of less than 1 ohm. To test for short filament to anode condition, connect ohmmeter between one of the filament terminals and the case of the magnetron (ground). This test should be indicated an infinite resistance. If a low or zero resistance reading is obtained then the magnetron should be replaced.
MICROWAVE OUTPUT POWER (1 Litre water load)
The following test procedure should be carried out with the microwave oven in a fully assembled condition (outer case fitted). Microwave output power from the magnetron can be measured by way of IEC 705, i.e. it can be measured by using water load how much it can be absorbed by the water load. To measure the microwave output power in the microwave oven, the relation of calorie and watt is used. When P(W) heating works for t(second), approximately P x t/4.187 calorie is generated. On the other hand, if the temperature of the water with V(ml) rises DeltaT (°C) during this microwave heating period, the calorie of the water is V x DeltaT.
Isolate the magnetron from high voltage circuit by removing all leads connected to filament terminal. To test for an open circuit filament use an ohmmeter to make a continuity test between the magnetron filament terminals, the meter should show a reading of less than 1 ohm. To test for short filament to anode condition, connect ohmmeter between one of the filament terminals and the case of the magnetron (ground). This test should be indicated an infinite resistance. If a low or zero resistance reading is obtained then the magnetron should be replaced.
MICROWAVE OUTPUT POWER (1 Litre water load)
The following test procedure should be carried out with the microwave oven in a fully assembled condition (outer case fitted). Microwave output power from the magnetron can be measured by way of IEC 705, i.e. it can be measured by using water load how much it can be absorbed by the water load. To measure the microwave output power in the microwave oven, the relation of calorie and watt is used. When P(W) heating works for t(second), approximately P x t/4.187 calorie is generated. On the other hand, if the temperature of the water with V(ml) rises DeltaT (°C) during this microwave heating period, the calorie of the water is V x DeltaT.
Measuring condition:
1. Container
The
water container must be a cylindrical borosilicate glass vessel having a
maximum material thickness of 3 mm and an outside diameter of
approximately 190 mm.
2. Temperature of the oven and vessel
The oven and the empty vessel are at ambient temperature prior to the start the test.
3. Temperature of the water
The initial temperature of the water is (10±2)°C.
4.
Select the initial and final water temperature so that the maximum
difference between the final water temperature and the ambient
temperature is 5˚C.
5. Select stirring devices and measuring instruments in order to minimize addition or removal of heat.
6. The graduation of the thermometer must be scaled by 0.1°C at minimum and accurate thermometer.
7. The water load must be (1000±5) g.
8. “t” is measured while the microwave generator is operating at full power. Magnetron filament heatup time is not included.
NOTE: The operation time of the microwave oven is “t + 2” sec. 2 sec. is magnetron filament heat-up time.
Measuring method:
1. Measure the initial temperature of the water before the water is added to the vessel.
(Example: The initial temperature T1 = 11°C)
2. Add the 1 litre water to the vessel.
3. Place the load on the centre of the shelf.
4. Operate the microwave oven at HIGH for the temperature of the water rises by a value Delta T of (10 ± 2)˚C.
5. Stir the water to equalize temperature throughout the vessel.
6. Measure the final water temperature. (Example: The final temperature T2 = 21°C)
7. Calculate the microwave power output P in watts from above formula.
JUDGMENT:
The measured output power should be at least ± 15 % of the rated output power.
CAUTION: 1°C CORRESPONDS TO 100 WATTS REPEAT MEASUREMENT IF THE POWER IS INSUFFICIENT.
CAUTION: 1°C CORRESPONDS TO 100 WATTS REPEAT MEASUREMENT IF THE POWER IS INSUFFICIENT.
POWER
TRANSFORMER TEST
High
voltages and large currents are present at the secondary winding and filament
winding of the power transformer. It is very dangerous to work near this part
when the oven is on. NEVER make any voltage measurements of the high-voltage circuits,
including the magnetron filament.
CARRY
OUT 3D CHECKS.
Disconnect the leads to the primary winding of the power transformer. Disconnect the filament and secondary winding connections from the rest of the HV circuitry. Using an ohmmeter, set on a low range, it is possible to check the continuity of all three windings. The following readings should be obtained:
a. Primary winding ................... approx. 1.3 Ohms
b. Secondary winding ............... approx. 87 Ohms
c. Filament winding .................. less than 1Ohms
If the reading obtained are not stated as above, then the power transformer is probably faulty and should be replaced.
Disconnect the leads to the primary winding of the power transformer. Disconnect the filament and secondary winding connections from the rest of the HV circuitry. Using an ohmmeter, set on a low range, it is possible to check the continuity of all three windings. The following readings should be obtained:
a. Primary winding ................... approx. 1.3 Ohms
b. Secondary winding ............... approx. 87 Ohms
c. Filament winding .................. less than 1Ohms
If the reading obtained are not stated as above, then the power transformer is probably faulty and should be replaced.
CARRY
OUT 4R CHECKS
HIGH
VOLTAGE RECTIFIER ASSEMBLY TEST
HIGH VOLTAGE RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be tested using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal B+C of the high voltage rectifier and note the reading obtained. Reverse the meter leads and note this second reading. The normal resistance is infinite in one direction and more than 100 kΩ in the other direction.
HIGH VOLTAGE RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be tested using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal B+C of the high voltage rectifier and note the reading obtained. Reverse the meter leads and note this second reading. The normal resistance is infinite in one direction and more than 100 kΩ in the other direction.
CARRY
OUT 4R CHECKS.
ASYMMETRIC RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric can be tested using an ohmmeter set to its highest range across the terminals A+B of the asymmetric rectifier and note the reading obtained. Reverse the meter leads and note this second reading. If an open circuit is indicated in both direction then the asymmetric rectifier is good. If an asymmetric rectifier is shorted in either direction, then the asymmetric rectifier is probably faulty and must be replaced with high voltage rectifier. When the asymmetric rectifier is defective, check whether magnetron, high voltage rectifier, high voltage wire or filament winding of the power transformer is shorted.
ASYMMETRIC RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric can be tested using an ohmmeter set to its highest range across the terminals A+B of the asymmetric rectifier and note the reading obtained. Reverse the meter leads and note this second reading. If an open circuit is indicated in both direction then the asymmetric rectifier is good. If an asymmetric rectifier is shorted in either direction, then the asymmetric rectifier is probably faulty and must be replaced with high voltage rectifier. When the asymmetric rectifier is defective, check whether magnetron, high voltage rectifier, high voltage wire or filament winding of the power transformer is shorted.
CARRY
OUT 4R CHECKS.
NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF THE MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BECAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.
NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF THE MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BECAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.
HIGH
VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
A. Isolate the high voltage capacitor from the circuit.
B. Continuity check must be carried out with measuring instrument which is set to the highest resistance range.
C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10MΩ after it has been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 MΩ because of its internal 10MΩ resistance.
F. When the internal wire is opened in the high voltage capacitor shows an infinite resistance.
G. The resistance across all the terminals and the chassis must be infinite when the capacitor is normal. If incorrect reading are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS.
CARRY OUT 3D CHECKS.
A. Isolate the high voltage capacitor from the circuit.
B. Continuity check must be carried out with measuring instrument which is set to the highest resistance range.
C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10MΩ after it has been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 MΩ because of its internal 10MΩ resistance.
F. When the internal wire is opened in the high voltage capacitor shows an infinite resistance.
G. The resistance across all the terminals and the chassis must be infinite when the capacitor is normal. If incorrect reading are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS.
SWITCH
TEST
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the following table.
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the following table.
If incorrect readings are
obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
CARRY OUT 4R CHECKS.
TEMPERATURE
FUSE AND THERMAL CUT-OUT TEST
CARRY
OUT 3D CHECKS.
Disconnect the leads from the terminals of the temperature fuse or thermal cut-out. Then using an ohmmeter, make a continuity test across the two terminals as described in the table below.
CARRY OUT 4R CHECKS.
Disconnect the leads from the terminals of the temperature fuse or thermal cut-out. Then using an ohmmeter, make a continuity test across the two terminals as described in the table below.
CARRY OUT 4R CHECKS.
If
incorrect readings are obtained, replace the temperature fuse or thermal
cut-out. An open circuit thermal cut-out
95˚C (MG) indicates that the magnetron has overheated, this may be due to
redistricted ventilation, cooling fan failure or a fault condition within the
magnetron or HV circuit. An open circuit
thermal cut-out 125˚C (OVEN) indicates that the foods in the oven may catch
fire, this may be due to over heating produced by improper setting of the
cooking time or failure of the control panel.
MONITOR
RESISTOR TEST
CARRY
OUT 3D CHECKS.
Disconnect the leads from the monitor resist. Using an ohmmeter and set on a low range. Check between the terminals of the monitor resistor. The resistance of monitor resistor is approx. 0.8 ohms. If incorrect readings are obtained, replace the monitor resistor.
CARRY OUT 4R CHECKS.
Disconnect the leads from the monitor resist. Using an ohmmeter and set on a low range. Check between the terminals of the monitor resistor. The resistance of monitor resistor is approx. 0.8 ohms. If incorrect readings are obtained, replace the monitor resistor.
CARRY OUT 4R CHECKS.
MOTOR
WINDING TEST
CARRY
OUT 3D CHECKS.
Disconnect the leads from the motor.
Using an ohmmeter, check the resistance between the two terminals as described in the table below.
Disconnect the leads from the motor.
Using an ohmmeter, check the resistance between the two terminals as described in the table below.
If
incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS
CARRY OUT 4R CHECKS
BLOWN
FUSE F M8A
CARRY
OUT 3D CHECKS.
1. If the fuse M8A is blown, there could be shorts or ground in electrical parts or wire harness. Check them and replace the defective parts or repair the wire harness.
2. If the fuse M8A is blown when the door is opened, check the 2nd. latch switch, monitor switch and monitor resistor. If the fuse M8A is blown by incorrect door switching replace the defective switch(s) and the fuse M8A.
3. If the fuse M8A is blown, there could be a short in the asymmetric rectifier or there could be a ground in wire harness. A short in the asymmetric rectifier may have occurred due to short or ground in H.V. rectifier, magnetron, power transformer or H.V. wire. Check them and replace the defective parts or repair the wire harness.
CARRY OUT 4R CHECKS.
CAUTION: ONLY REPLACE FUSE M8A WITH THE CORRECT VALUE REPLACEMENT
1. If the fuse M8A is blown, there could be shorts or ground in electrical parts or wire harness. Check them and replace the defective parts or repair the wire harness.
2. If the fuse M8A is blown when the door is opened, check the 2nd. latch switch, monitor switch and monitor resistor. If the fuse M8A is blown by incorrect door switching replace the defective switch(s) and the fuse M8A.
3. If the fuse M8A is blown, there could be a short in the asymmetric rectifier or there could be a ground in wire harness. A short in the asymmetric rectifier may have occurred due to short or ground in H.V. rectifier, magnetron, power transformer or H.V. wire. Check them and replace the defective parts or repair the wire harness.
CARRY OUT 4R CHECKS.
CAUTION: ONLY REPLACE FUSE M8A WITH THE CORRECT VALUE REPLACEMENT
NOISE
FILTER TEST
CARRY
OUT 3D CHECKS.
Disconnect the leads from the terminals of the noise filter. Using an ohmmeter, check between the terminals as described in the following table.
Disconnect the leads from the terminals of the noise filter. Using an ohmmeter, check between the terminals as described in the following table.
If
incorrect readings are obtained, replace the noise filter unit.
CARRY OUT 4R CHECKS.
CARRY OUT 4R CHECKS.
TOUCH
CONTROL PANEL ASSEMBLY TEST
The
touch control panel consists of circuits including semiconductors such
as LSI, ICs, etc. Therefore, unlike conventional microwave ovens, proper
maintenance cannot be performed with only a voltmeter and ohmmeter. In
this service manual, the touch control panel assembly is divided into
Liquid crystal display, rubber connector, Control Unit and Key Unit, and
troubleshooting by replacement is described according to the symptoms
indicated.
1. Key Unit.
Note: Check key unit ribbon connection before replacement. The
following symptoms indicate a defective key unit. Replace the key unit.
a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.
2. Control Panel.
The
following symptoms indicate a defective control unit. Before replacing
the control unit, perform the Key unit test (Procedure L) to determine
if control unit is faulty.
2-1 In connection with pads.
a) When touching the pads, a certain group of pads do not produce a signal.
b) When touching the pads, no pads produce a signal.
2-2 In connection with indicators.
a)
At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 Other possible troubles caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 Other possible troubles caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.
KEY
UNIT TEST
If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon is making good contact, verify that the door sensing switch (stop switch) operates properly; that is the contacts are closed when the door is closed and open when the door 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 door sensing switch is closed (either close the door or short the door sensing switch connector). Use the key unit matrix indicated on the control panel schematic and place a jumper wire between the pins that correspond to the STOP/CLEAR pad making momentary contact. If the control unit responds by clearing with a beep the key unit is faulty and must be replaced. If the control unit does not respond, it is faulty and must be replaced. If a specific pad does not respond, the above method may be used (after clearing the control unit) to determine if the control unit or key pad is at fault.
If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon is making good contact, verify that the door sensing switch (stop switch) operates properly; that is the contacts are closed when the door is closed and open when the door 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 door sensing switch is closed (either close the door or short the door sensing switch connector). Use the key unit matrix indicated on the control panel schematic and place a jumper wire between the pins that correspond to the STOP/CLEAR pad making momentary contact. If the control unit responds by clearing with a beep the key unit is faulty and must be replaced. If the control unit does not respond, it is faulty and must be replaced. If a specific pad does not respond, the above method may be used (after clearing the control unit) to determine if the control unit or key pad is at fault.
RELAY TEST
Remove
the outer case and check voltage between Pin No. 3 of the 2-pin
connector (A) and the common terminal of the relay RY2 on the control
unit with an A.C. voltmeter. The meter should indicate 230 - 240 volts,
if not check oven circuit.
RY1 and RY2 Relay Test
These 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.
PROCEDURES
TO BE TAKEN WHEN THE FOIL PATTERN ON THE PRINTED WIRING BOARD (PWB) IS OPEN
To
protect the electronic circuits, this model is provided with a fine foil
pattern added to the primary on the PWB, this foil pattern acts as a fuse. If
the foil pattern is open, follow the troubleshooting guide given below for
repair.
Problem:
POWER ON, indicator does not light up.
