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R-879SL (serv.man7)
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Service Manual
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Device
Home Appliance / Microwave Oven / Test Procedures
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r-879sl-sm7.pdf
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Sharp R-879SL (serv.man7) Service Manual ▷ View online

R879(W)
8 – 2
[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 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 k
Ω 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
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 rectifier. 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 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 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] 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] 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 to Pin No's C1
and C3 of the thermistor harness.
If the meter does not indicate above resistance, replace the thermistor.
CARRY OUT 4R CHECKS.
[7] G: THERMAL CUT-OUT TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the thermal cut-out. Then using an ohmmeter, make a continuity test across the two terminals as described
in the below.
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.
Room Temperature
Resistance
20
°C - 30°C
Approximately 359.9 k
Ω - 152 kΩ
D2
D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE
RECTIFIER
A
B
C
R879(W)
8 – 3
If incorrect readings are obtained, replace the thermal cut-out.
An open circuit thermal cut-out (MG) indicates that the magnetron has overheated, this may be due to resistricted ventilation, cooling fan failure.
An open circuit thermal cut-out (OVEN) indicates that the oven cavity has overheated, this may be due to no load operation, or excessive heat / fire
inside the oven.
CARRY OUT 4R CHECKS.
[8] H: 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.
[9] 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] J: BLOWN FUSE (F1) 20A
CARRY OUT 3D CHECKS.
If the fuse 20A 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 with the correct value replacement.
[11] K: BLOWN FUSE F8A
CARRY OUT 3D CHECKS.
1. If the fuse F8A is blown when the door is opened, check the monitored latch switch and monitor switch.
2. If the fuse F8A is blown by incorrect door switching replace the defective switch(es) and the noise filter (fuse F8A).
3. If the fuse F8A is blown, there could be shorts in the asymmetric rectifier or there is a ground in wire harness. A short in the asymmetric rectifier
may be occurred due to short or ground in H.V. rectifier, magnetron, high voltage transformer or H.V. wire. Check them and replace the defective
parts or repair the wire harness.
CARRY OUT 4R CHECKS.
[12] L: GRILL HEATING ELEMENTS (TOP) AND BOTTOM HEATING ELEMENT TEST
CARRY OUT 3D CHECKS.
Before carrying out the following tests make sure the heating element is cool completely. 
1. Resistance of heater.
Disconnect the wire leads to the heating element to be tested. Using ohmmeter with low resistance range. Check the resistance across the termi-
nals of the heating element as described in the following table.
Table: Thermal Cut-out 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.)
Thermal cut-out TC1 125
°C
This is not resetable type.
Above 125
°C
Closed circuit
Thermal cut-out TC2 145
°C
Bellow  115
°C.
Above 145
°C
Closed circuit
Table: Resistance of Motor
Motors
Resistance
Fan motor
Approximately   399
Ω
Turntable motor
Approximately 14.7k
Ω
Convection fan motor
Approximately  288k
Ω
MEASURING POINT 
INDICATION OF OHMMETER
Between N and L 
Approx. 680 k
Ω
Between terminal N and WHITE 
Short circuit
Between terminal L and RED 
Short circuit
F8A
20A
WHT
RED
R1
R2
N
Cx
Cy
L
L
L
L (min) Cx ± 20% Cy ± 20%
R1
R2
1.0mH
0.22 uF
4700pF 10 M
680k
R879(W)
8 – 4
2. Insulation resistance.
Disconnect the wire leads to the heating element to be tested. Check the insulation resistance between the element terminal and cavity using a
500V - 100M
Ω insulation tester. The insulation resistance should be more than 10MΩ in the cold start.
If the results of above test 1 and/or 2 are out of above specifications, the heating element is probably faulty and should be replaced.
CARRY OUT 4R CHECKS.
[13] M: CONTROL PANEL ASSEMBLY TEST
The control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore, unlike conventional microwave ovens, proper main-
tenance can not be performed with only a voltmeter and ohmmeter.
In this service manual, the control panel assembly is divided into two units, 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.
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 Panel
The following symptoms indicate a defective control unit. Before replacing the control unit perform the key unit test (Procedure N) to determine if con-
trol unit is faulty.
2.1. In connection with pads
1) When touching the pads, a certain group of pads do not produce a signal.
2) When touching the pads, no pads produce a signal.
2.2. In connection with indicators
1) At a certain digit, all or some segments do not light up.
2) At a certain digit, brightness is low.
3) Only one indicator does not light up.
4) The corresponding segments of all digits do not light up; or they continue to light up.
5) Wrong figure appears.
6) A certain group of indicators do not light up.
7) The figure of all digits flicker.
2.3. Other possible troubles caused by defective control unit.
1) Buzzer does not sound or continues to sound.
2) Clock does not operate properly.
3) Cooking is not possible.
4) Proper temperature measurement is not obtained.
[14] N: KEY UNIT TEST
If the display fails to clear when the STOP/CLEAR pad is
depressed, first verify the ribbon cable is making good con-
tact, verify that the stop switch operates properly; that is the
contacts are closed when the door is closed and open when
the door is open. If the stop switch is good, disconnect the
flat ribbon cable that connects the key unit to the control unit
and make sure the stop switch is closed (either close the
door or short the stop 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 a 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.
CARRY OUT 4R CHECKS.
Table: Resistance of heater
Parts name
Resistance
Grill heating element (Top)
Approximately 48
Bottom heating element
Approximately 92
Ω
G2
G3
G4
G5
G6
G7
G8
G12
G11
G10
G9
G1
STOP
CLEAR
(WEIGHT)
PIZZA
COMBI
10min
KITCHEN TIMER
CLOCK SET
(WEIGHT)
WHOLE
POULTRY
ROAST
BEEF
RICE/
PASTA
CONV.
(ºC)
info
(TIME)
CHICKEN
QUARTERS
ROAST
POULTRY
CRISPY
COATED
FOODS
GRILL
1min
START
AUTO MINUTE
(TIME)
MEAT
JOINT
ROAST
PORK
CRISPY
CHIPS
MICRO
POWER
10sec
R879(W)
8 – 5
[15] O: RELAY TEST
CARRY OUT 3D CHECKS.
Remove the outer case and check voltage between Pin Nos. 5 and 7 of the 4 pin connector (E) on the control unit with an A.C. voltmeter. The meter
should indicate 230-240 volts, if not check oven circuit.
Relay Test
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation, grill operation, convection operation or dual 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.
[16] P: PROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE PRINTED WIRING
BOARD (PWB) IS OPEN
Problem: POWER ON, indicator does not light up.
CARRY OUT 3D CHECKS.
NOTE: *At the time of these repairs, make a visual inspection of the varistor for burn-
ing damage and examine the transformer with tester for the presence of layer
short circuit (check primary coil resistance).
If any abnormal condition is detected, replace the control unit.
CARRY OUT 4R CHECKS.
RELAY SYMBOL
OPERATIONAL VOLTAGE
CONNECTED COMPONENTS
RY1
APPROX. 18.0V D.C.
Oven lamp / Turntable motor
RY2
APPROX. 18.0V D.C.
High voltage transformer
RY3
APPROX. 24.0V D.C.
Grill (Top) heating element
RY4
APPROX. 24.0V D.C.
Bottom heating element
RY5
APPROX. 24.0V D.C.
Touch control transformer
RY6
APPROX. 24.0V D.C.
Fan motor
RY7
APPROX. 24.0V D.C.
Convection motor
STEPS
OCCURRENCE
CAUSE OR CORRECTION
1
The rated AC voltage is not present between Pin Nos. 5 and 7 of 
the 4-pin connector (E).
Check supply voltage and oven power cord.
2
The rated AC voltage is present at primary side of low voltage 
transformer.
Low voltage transformer or secondary circuit defective.
Check and replace the touch control transformer or the control unit.
4
Pattern at “a” is broken.
Replace the control unit. 
(CARRY OUT 3D CHECKS BEFORE REPAIR)
a
7
JP0
S1
CN-A
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  • Here you can View online or download the Service Manual for the Sharp R-879SL (serv.man7) in PDF for free, which will help you to disassemble, recover, fix and repair Sharp R-879SL (serv.man7) Microwave Oven. Information contained in Sharp R-879SL (serv.man7) Service Manual (repair manual) includes:
  • Disassembly, troubleshooting, maintenance, adjustment, installation and setup instructions.
  • Schematics, Circuit, Wiring and Block diagrams.
  • Printed wiring boards (PWB) and printed circuit boards (PCB).
  • Exploded View and Parts List.