Sharp R-890SLM Service Manual ▷ View online
R-890SLM
7 - 1
CHAPTER 7. TROUBLESHOOTING GUIDE
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” section.
IMPORTANT:
If the oven becomes inoperative because of a blown fuse F8A in the monitored latch switch - monitor switch circuit, check the monitored
latch switch and monitor switch before replacing the noise filter (fuse F8A).
Service_R-890SLM.indd 13
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R-890SLM
7 - 2
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BLOCKED
COOLING FAN
BLOCKED CONVECTION FAN
NO POWER AT WALL OUTLET
HOME FUSE OR BREAKER
MIS-ADJUSTMENT OF SWITCHES
BLOCKED VENTILATION OPENINGS
OPENED WIRE HARNESS
SHORTED WIRE HARNESS
NO POWER AT WALL OUTLET
HOME FUSE OR BREAKER
MIS-ADJUSTMENT OF SWITCHES
BLOCKED VENTILATION OPENINGS
OPENED WIRE HARNESS
SHORTED WIRE HARNESS
POWER SUPPLY CORD
FOIL PATTERN ON P.W.B.
RELAY RY7
RELAY RY6
RELAY RY5
RELAY RY4
RELAY RY3
RELAY RY2
RELAY RY1
JOG SWITCH UNIT
CONTROL PANEL ASSEMBLY
TC TRANSFORMER
BOTTOM GRILL HEATING ELEMENT
TOP GRILL HEATING ELEMENT
NOISE FILTER (FUSE F8A)
FUSE 20A
NOISE FILTER
CONVECTION FAN MOTOR
FAN MOTOR
TURNTABLE MOTOR
THERMAL CUT-OUT 145ºC (OVEN)
THERMAL CUT-OUT 125ºC (MG)
THERMISTOR
MONITOR SWITCH
STOP SWITCH
MONITORED LATCH SWITCH
HIGH VOLTAGE CAPACITOR
H.V. HARNESS
H.V. RECTIFIER ASSEMBLY
HIGH VOLTAGE TRANSFORMER
MAGNETRON
FOIL PATTERN ON P.W.B.
RELAY RY7
RELAY RY6
RELAY RY5
RELAY RY4
RELAY RY3
RELAY RY2
RELAY RY1
JOG SWITCH UNIT
CONTROL PANEL ASSEMBLY
TC TRANSFORMER
BOTTOM GRILL HEATING ELEMENT
TOP GRILL HEATING ELEMENT
NOISE FILTER (FUSE F8A)
FUSE 20A
NOISE FILTER
CONVECTION FAN MOTOR
FAN MOTOR
TURNTABLE MOTOR
THERMAL CUT-OUT 145ºC (OVEN)
THERMAL CUT-OUT 125ºC (MG)
THERMISTOR
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STOP SWITCH
MONITORED LATCH SWITCH
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R-890SLM
8 - 1
CHAPTER 8. TEST PROCEDURES
[1] A: 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 CHECKS.
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
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
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.
1. MICROWAVE OUTPUT POWER
The power output of this oven is rated using the method specified by IEC 60705. Full details of how to curry out this procedure can be
found in the Sharp Technical Training notes which is available from Sharp Parts Centre (part number SERV-LITMW01).
The IEC60705 procedure must be carried out using laboratory-type procedures and equipment.
These requirements make the procedure unsuitable for routine performance checks.
NOTE:
The IEC60705 procedure must be carried out using laboratory-type procedures and equipment.
These requirements make the procedure unsuitable for routine performance checks.
NOTE:
The following test method gives an indication of the output power only, it cannot be used to establish the actual/rated
output power. If the true output power is required, then the IEC60705 test method must be used.
Alternative simplified method:
1. Place 2 litres of cold water (between 12°C and 20°C) in a suitable container.
2. Stir the water and measure the temperature in °C. Note temperature as T1.
3. Place the container in the microwave and heat the water for 1 minute and 36 seconds on full power.
NOTE:
1. Place 2 litres of cold water (between 12°C and 20°C) in a suitable container.
2. Stir the water and measure the temperature in °C. Note temperature as T1.
3. Place the container in the microwave and heat the water for 1 minute and 36 seconds on full power.
NOTE:
The operation time of the microwave oven includes “3” sec. (3 sec. is magnetron filament heat-up time.)
4. When the 1 minute and 36 seconds is completed, remove the container and stir the water. Note the water temperature as T2.
5. Calculate the output power using the following formula:
R.F. Power Output = (T2 - T1) x 90.
NOTE: The result from this test should be within the allowance of 2000cc alternative method. (±10%).
5. Calculate the output power using the following formula:
R.F. Power Output = (T2 - T1) x 90.
NOTE: The result from this test should be within the allowance of 2000cc alternative method. (±10%).
2. MICROWAVE LEAKAGE TEST
This oven should be tested for microwave leakage on completion of any repair or adjustment, following the procedure described in
the Sharp Technical Training notes (part number SERV-LITMW01). The maximum leakage permitted in BS EN 60335-2-25 is 50W/m
2
(equivalent to 5W/m
2
), however it is not normal to detect any significant leakage, therefore, any leakage which is detected should be
investigated.
It is essential that only leakage detectors with current calibration traceable to National Physical Laboratories are used.
It is essential that only leakage detectors with current calibration traceable to National Physical Laboratories are used.
Suitable leakage detectors: CELTEC A100
APOLLO X1
[2] B: HIGH VOLTAGE TRANSFORMER TEST
WARNING:
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.
1. CARRY OUT 3D CHECKS.
2. Disconnect the leads to the primary winding of the high voltage transformer. Disconnect the filament and secondary winding
2. Disconnect the leads to the primary winding of the high voltage 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 winding. The following readings should be obtained:
a.Primary winding -------------------- approximately 2.1 Ω
b.Secondary winding --------------- approximately 133 Ω
c.Filament winding --------------------------- less than 1 Ω
If the readings obtained are not stated as above, then the high voltage transformer is probably faulty and should be replaced.
3. Also, the high voltage transformer has the thermal cut-out in the primary coil. The thermal cut-out will open when the temperature
3. Also, the high voltage transformer has the thermal cut-out in the primary coil. The thermal cut-out will open when the temperature
of the thermal cut-out in the primary coil reaches approximately 150°C. The thermal cut-out resets automatically at 130°C. If an
ohmmeter indicates an open circuit under normal condition, replace the high voltage transformer because the primary coil (thermal
cut-out) has opened. An open primary coil (thermal cut-out) indicates overheating of the high voltage transformer. Check for
restricted air flow to the high voltage transformer, especially the ventilation opening.
4. CARRY OUT 4R CHECKS.
Service_R-890SLM.indd 15
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R-890SLM
D2
D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE
RECTIFIER
A
B
C
[3] C: 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
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
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 rectifier can be
CARRY OUT 4R CHECKS.
ASYMMETRIC RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier 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 directions then the asymmetric rectifier is good. If the
asymmetric rectifier is shorted in either direction, then the asymmetric rectifier is faulty and must be replaced with high voltage recti-
fier. When the asymmetric rectifier is defective, check whether magnetron, high voltage rectifier, high voltage wire or filament winding
of the high voltage transformer is shorted.
CARRY OUT 4R CHECKS.
NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF THE MEASURING INSTRUMENT
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.
[4] D: HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
1. Isolate the high voltage capacitor from the circuit.
2. Continuity check must be carried out with measuring instrument which is set to the highest resistance range.
3. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10MΩ after it has been charged.
4. A short-circuited capacitor shows continuity all the time.
5. An open capacitor constantly shows a resistance about 10 MΩ because of its internal 10MΩ resistance.
6. When the internal wire is opened in the high voltage capacitor shows an infinite resistance.
7. 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.
1. Isolate the high voltage capacitor from the circuit.
2. Continuity check must be carried out with measuring instrument which is set to the highest resistance range.
3. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10MΩ after it has been charged.
4. A short-circuited capacitor shows continuity all the time.
5. An open capacitor constantly shows a resistance about 10 MΩ because of its internal 10MΩ resistance.
6. When the internal wire is opened in the high voltage capacitor shows an infinite resistance.
7. 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.
[5] E: 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.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the following table.
Table: Terminal Connection of Switch
Plunger Operation
Common terminal to Normally open terminal
Common terminal to Normally close terminal
Released
Open circuit
Short circuit
Depressed
Short circuit
Open circuit
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
CARRY OUT 4R CHECKS.
[6] F: THERMISTOR TEST
CARRY OUT 3D CHECKS.
Disconnect the connector B from CPU unit. Measure the resistance of the thermistor with an ohmmeter. Connect the ohmmeter leads
Disconnect the connector B from CPU unit. Measure the resistance of the thermistor with an ohmmeter. Connect the ohmmeter leads
to Pin No’s C1 and C3 of the thermistor harness.
Room Temperature
Resistance
20°C - 30°C
Approximately 359.9 kΩ - 152 kΩ
If the meter does not indicate above resistance, replace the thermistor.
CARRY OUT 4R CHECKS.
CARRY OUT 4R CHECKS.
8 - 2
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