R-238ASL (serv.man8). Test Procedures - Sharp Home Appliance Service Manual (repair manual)

r-238asl (serv.man8) service manual
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R-238ASL (serv.man8)
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Service Manual
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Device
Home Appliance / Microwave Oven / Test Procedures
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r-238asl-sm8.pdf
Date

Read Sharp R-238ASL (serv.man8) Service Manual online

R238A(SL)
8 – 1
R238A(SL)
Service Manual
 
CHAPTER 8. 
TEST PROCEDURES
[1] Procedure A: MAGNETRON TEST
1. CARRY OUT 3D CHECKS.
2. To test for an open filament, isolate the magnetron from the high voltage circuit. A continuity check across the magnetron filament leads should
indicate less than 1 ohm.
3. To test for a shorted magnetron, connect the ohmmeter leads between the magnetron filament leads and chassis ground. This test should indicate
an infinite resistance. If there is little or no resistance the magnetron is grounded and must be replaced.
4. Reconnect all leads removed from components during testing.
5. Reinstall the outer case (cabinet).
6. Reconnect the power supply cord after the outer case is installed.
7. Run the oven and check all functions.
1. MICROWAVE OUTPUT POWER
The following test procedure should be carried out with the microwave oven in a fully assembled condition (outer case fitted).
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 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 48 seconds on full power.
NOTE: The operation time of microwave oven includes “3” sec. (3 sec. is magnetron filament heat-up time.)
4. When the 1 minute and 48 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 80.
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 Techni-
cal 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.
Suitable leakage detectors: CELTEC A100
                                                 APOLLO X1
[2] Procedure B: HIGH VOLTAGE TRANSFORMER TEST
1. CARRY OUT 3D CHECKS.
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 -------------------- 2.8 ohms approximately
                  b.Secondary winding --------------- 204 ohms approximately 
                  c.Filament winding ------------------------------ less than 1 ohm
If the readings obtained are not stated as above, then the high voltage transformer is probably faulty and should be replaced.
 NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL WHILE THE OVEN IS IN OPERATION.
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 cir-
cuits, including the magnetron filament.
R238A(SL)
8 – 2
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 cir-
cuit 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.
[3] Procedure 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 highest range.
Connect the ohmmeter across the terminal 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 k
Ω in the other direction.
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 DIRECTION.
[4] Procedure 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 10M
Ω 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 M
Ω 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] Procedure 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.
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
[6] Procedure F: TEMPERATURE FUSE TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the temperature fuse. Then using an ohmmeter, make a continuity test across the two terminals as
described in the below.
If incorrect readings are obtained, replace the temperature fuse.
An open circuit temperature fuse (OVEN) indicates that the food in the oven cavity may catch fire, this may be due to overheating produced by
improper setting of the cooking time or failure of the control panel.
CARRY OUT 4R CHECKS.
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.
Table: Temperature Fuse Test
Parts Name
Temperature of “ON” condition 
(closed circuit).
Temperature of “OFF” condition 
(open circuit).
Indication of ohmmeter (When room 
temperature is approx. 20
°C.)
Temperature fuse 150
°C
This is not resetable type.
Above 150
°C
Closed circuit
R238A(SL)
8 – 3
[7] Procedure G: 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.
If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS.
[8] Procedure H: FUSE T6.3A
CARRY OUT 3D CHECKS.
If the fuse T6.3A is blown when the door is opened, check the 1st. latch switch, rely (RY1), 2nd. interlock relay (RY2) and monitor switch.
If the fuse T6.3A is blown by incorrect door switching replace the defective switch(es) and the fuse T6.3A.
If the fuse T6.3A is blown, there is a shorts or grounds in electrical parts or wire harness. Check them and replace the defective parts or repair the
wire harness.
CARRY OUT 4R CHECKS.
CAUTION: ONLY REPLACE FUSE T6.3A WITH THE CORRECT VALUE REPLACEMENT.
[9] Procedure I: 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. 
If incorrect readings are obtained, replace the noise filter unit.
CARRY OUT 4R CHECKS.
[10] Procedure J: HIGH VOLTAGE FUSE TEST
CARRY OUT 3D CHECKS.
If the high voltage fuse is blown, there could be a short in the high voltage rectifier or the magnetron.
Check them and replace the defective parts and the high voltage fuse.
CARRY OUT 4R CHECKS.
CAUTION: ONLY REPLACE HIGH VOLTAGE FUSE WITH THE CORRECT VALUE REPLACEMENT. 
[11] Procedure K: 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 two
units, Control Unit and Key Unit, and also the Control Unit is divided into two units, CPU Unit and Power Unit, and troubleshooting by unit 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.
1) When touching the pads, a certain pad produces no signal at all.
2) When touching a number pad, two figures or more are displayed.
3) When touching the pads, sometimes a pad produces no signal.
2. Control Unit.
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. 
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) In connection with indicators.
Table: Resistance of Motor
Motors
Resistance
Fan motor
Approximately 250 
Ω
Turntable motor
Approximately 14.7 k
Ω
MEASURING POINT 
INDICATION OF OHMMETER
Between N and L 
Open circuit
Between terminal N and WHITE 
Short circuit
Between terminal L and RED 
Short circuit
RED
WHT
FUSE
T6.3A
N
L
NOISE SUPPRESSION COIL
NOISE FILTER
R238A(SL)
8 – 4
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 up. 
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.
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.
[12] Procedure L: KEY UNIT (MEMBRANE SWITCH) TEST
1. CARRY OUT 3D CHECKS.
2. Isolate the key unit with the control panel frame to be tested.
3. Using an ohmmeter and referring to the key unit matrix indicated on the control unit circuit, check the circuit between the pins of the key unit that
correspond to the STOP/CLEAR key. When the pad is pressed, the ohmmeter should indicate short circuit. When the pad is released, the ohmme-
ter should indicate open circuit. If incorrect readings are obtained, the key unit is faulty and must be replaced. About the other pads, the above
method may be used.
4. CARRY OUT 4R CHECKS.
[13] Procedure M: RELAY TEST
CARRY OUT 3D CHECKS.
Remove the outer case and check voltage between the normal open terminal of the relay RY1 and the normal open 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.
CARRY OUT 4R CHECKS.
RELAY SYMBOL
OPERATIONAL VOLTAGE
CONNECTED COMPONENTS
RY1
Approx. 12.6V D.C.
Oven lamp / Turntable motor / Cooling fan motor
RY2
Approx. 12.3V D.C.
High voltage transformer
Pin NO. G1
Pin NO. G10
Key unit ribbon
cable
Key unit (Membrane Switch) front view
POWER
LEVEL
10min.
CHICKEN
QUARTERS
WHOLE
POULTRY
MEAT
JOINT
(TIME)
(TIME)
(WEIGHT)
(WEIGHT)
STOP
CLEAR
10sec.
1min.
ROAST
POULTRY
ROAST
PORK
ROAST
BEEF / LAMB
AUTO
COOK
START
AUTO MINUTE
KITCHEN TIMER
CLOCK SET
G1
G2
G3
G4
G5
G6
G7
G8
G9
G10
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