Sharp R-26ST-A User manual

CHAPTER 1. BEFORE SERVICING
CHAPTER 2. WARNING TO SERVICE PERSONNEL
CHAPTER 3. PRODUCT SPECIFICATIONS
CHAPTER 4. APPEARANCE VIEW
CHAPTER 5. OPERATION SEQUENCE
CHAPTER 6. FUNCTION OF IMPORTANT COMPO-
NENTS
CHAPTER 7. TROUBLESHOOTING GUIDE
CHAPTER 8. TEST PROCEDURES
CHAPTER 9. TOUCH CONTROL PANEL ASSEMBLY
CHAPTER 10. PRECAUTIONS FOR USING LEAD-
FREE SOLDER
CHAPTER 11. COMPONENT REPLACEMENT AND
ADJUSTMENT PROCEDURE
CHAPTER 12. MICROWAVE MEASUREMENT
CHAPTER 13. TEST DATA AT A GLANCE
CHAPTER 14. CIRCUIT DIAGRAMS
Parts List
S9905R26STPHA
MICROWAVE OVEN
R-26ST-A
SERVICE MANUAL
R26STA
MODEL
CONTENTS
This document has been published to be used for
after sales service only.
The contents are subject to change without notice.
TopPage
In the interests of user-safety the oven should be restored to its original condition and only parts identical to those
specified should be used.

CONTENTS
CHAPTER 1. BEFORE SERVICING
[1] GENERAL IMPORTANT INFORMA-
TION ........................................................... 1-1
[2] WARNING................................................... 1-1
[3] CAUTION MICROWAVE RADIATION ........ 1-2
CHAPTER 2. WARNING TO SERVICE PERSON-
NEL
CHAPTER 3. PRODUCT SPECIFICATIONS
CHAPTER 4. APPEARANCE VIEW
[1] OVEN.......................................................... 4-1
[2] TOUCH CONTROL PANEL ........................ 4-1
CHAPTER 5. OPERATION SEQUENCE
[1] OFF CONDITION........................................ 5-1
[2] MICROWAVE COOKING CONDITION....... 5-1
[3] POWER OUTPUT REDUCTION ................ 5-1
CHAPTER 6. FUNCTION OF IMPORTANT COM-
PONENTS
[1] DOOR OPEN MECHANISM ....................... 6-1
[2] SECONDARY INTERLOCK SWITCH
(SW1).......................................................... 6-1
[3] DOOR SENSING SWITCH (SW3).............. 6-1
[4] MONITOR SWITCH (SW2)......................... 6-1
[5] FUSE (F1) T6.3A ........................................ 6-1
[6] TEMPERATURE FUSE (TF) 150C (OV-
EN).............................................................. 6-1
[7] ASYMMETRIC RECTIFIER ........................ 6-1
[8] TURNTABLE MOTOR (TTM)...................... 6-1
[9] FAN MOTOR (FM) ...................................... 6-1
[10] NOISE FILTER............................................ 6-1
CHAPTER 7. TROUBLESHOOTING GUIDE
CHAPTER 8. TEST PROCEDURES
[1] A : MAGNETRON (MG) TEST.................... 8-1
[2] B: HIGH VOLTAGE TRANSFORMER (T)
TEST........................................................... 8-2
[3] C: HIGH VOLTAGE RECTIFIER TEST....... 8-2
[4] D: HIGH VOLTAGE CAPACITOR (C)
TEST........................................................... 8-2
[5] E: SWITCH (SW1, SW2, SW3) TEST ........ 8-3
[6] F: TEMPERATURE FUSE (TF) TEST ........ 8-3
[7] G: MOTOR WINDING TEST....................... 8-3
[8] H: FUSE (F1) T6.3A.................................... 8-3
[9] I: NOISE FILTER TEST .............................. 8-3
[10] J: TOUCH CONTROL PANEL ASSEM-
BLY TEST ................................................... 8-4
[11] K: SWITCH UNIT TEST.............................. 8-4
[12] L: RELAY (RY1, RY2) TEST ....................... 8-4
[13] M: PROCEDURES TO THE CONTROL
UNIT............................................................ 8-5
CHAPTER 9. TOUCH CONTROL PANEL ASSEM-
BLY
[1] OUTLINE OF TOUCH CONTROL PAN-
EL ............................................................... 9-1
[2] SERVICING FOR TOUCH CONTROL
PANEL ........................................................ 9-1
CHAPTER 10. PRECAUTIONS FOR USING LEAD-
FREE SOLDER
CHAPTER 11. COMPONENT REPLACEMENT
AND ADJUSTMENT PROCEDURE
[1] BEFORE OPERATING ..............................11-1
[2] OUTER CASE REMOVAL .........................11-1
[3] HIGH VOLTAGE TRANSFORMER RE-
MOVAL.......................................................11-2
[4] HIGH VOLTAGE RECTIFIER ASSEM-
BLY AND HIGH VOLTAGE CAPACITOR
REMOVAL..................................................11-2
[5] MAGNETRON REMOVAL .........................11-2
[6] POSITIVE LOCK CONNECTOR (NO-
CASE TYPE) REMOVAL ...........................11-2
[7] TURNTABLE MOTOR REMOVAL .............11-2
[8] COOLING FAN MOTOR REMOVAL..........11-3
[9] POWER SUPPLY CORD REPLACE-
MENT.........................................................11-3
[10] CONTROL PANEL ASSEMBLY RE-
MOVAL.......................................................11-4
[11] SECONDARY INTERLOCK SWITCH,
DOOR SENSING SWITCH AND MONI-
TOR SWITCH ADJUSTMENT ...................11-4
[12] SECONDARY INTERLOCK SWITCH,
DOOR SENSING SWITCH AND MONI-
TOR SWITCH ADJUSTMENT ...................11-4
[13] DOOR REPLACEMENT ............................11-5
CHAPTER 12. MICROWAVE MEASUREMENT
CHAPTER 13. TEST DATA AT A GLANCE
CHAPTER 14. CIRCUIT DIAGRAMS
[1] Oven Schematic........................................ 14-1
[2] Pictorial Diagram (Figure S-1) .................. 14-3
[3] Control Unit Circuit (Figure S-2)................ 14-4
[4] Printed Wiring Board ................................ 14-5
Parts List

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[3] CAUTION MICROWAVE RADIATION
Personnel should not be exposed to the microwave energy which may radiate from the
magnetron or other microwave generating devices if it is improperly used or connected.
All input and output microwave connections, waveguides, flanges and gaskets must be
secured.
Never operate the device without a microwave energy absorbing load attached.
Never look into an open waveguide or antenna while the device is energized.

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[2] B: HIGH VOLTAGE TRANSFORMER (T) 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 -------------------- 2.52 ohms approximately
b.Secondary winding --------------- 216 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.
3. CARRY OUT 4R CHECKS.
[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 kΩin 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 (C) 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 10MΩafter it has been charged.
4. A short-circuited capacitor shows continuity all the time.
5. An open capacitor constantly shows a resistance about 10 MΩbecause of its internal 10MΩresistance.
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.
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.
1000g
1000g
1000g
T1 C T2 C
Heat up for 55 sec.
D2 D1
ASYMMETRIC
RECTIFIER HIGH VOLTAGE
RECTIFIER
AB
C

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[5] E: SWITCH (SW1, SW2, SW3) 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: TEMPERATURE FUSE (TF) 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.
[7] 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] H: FUSE (F1) T6.3A
CARRY OUT 3D CHECKS.
If the fuse F1 T6.3A is blown when the door is opened, check the secondary interlock switch SW1, primary interlock relay RY2 and monitor switch
SW2.
If the fuse F1 T6.3A is blown by incorrect door switching replace the defective switch(es) and the fuse F1 T6.3A.
If the fuse F1 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 F1 T6.3A WITH THE CORRECT VALUE REPLACEMENT.
[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.
Table: Terminal Connection of Switch
Plunger Operation COM to NO COM to NC COM; Common terminal
Released Open circuit Short circuit NO; Normally open terminal
Depressed Short circuit Open circuit. NC; Normally close terminal
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
Table: Resistance of Motor
Fan Motors Turntable motor
Part Code RMOTEA405WRZZ RMOTDA289WRZZ RMOTDA173WRE0 RMOTDA253WRZZ
Resistance Approximately 388ΩApproximately 13.5kΩApproximately 12.2kΩApproximately 14.5kΩ
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
F1:
NL
NOISE SUPPRESSION COIL
NOISE FILTER

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[10] J: 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 Switch Unit, and also the Control Unit is divided into two units, CPU Unit and Power Unit, and troubleshooting by unit replace-
ment is described according to the symptoms indicated.
1. Switch Unit. Note: Check switch unit wire harness connection before replacement.
The following symptoms indicate a defective switch unit. Replace the switch unit.
1) When touching the buttons, a certain button produces no signal at all.
2) When touching the buttons, sometimes a button produces no signal.
3) When rotating the TIMER/WEIGHT knob, the cooking time or the weight can not be input.
2. Control Unit.
The following symptoms indicate a defective control unit. Before replacing the switch unit, perform the Switch unit test (Procedure L) to determine
if control unit is faulty.
1) In connection with buttons.
a) When touching the buttons, a certain group of buttons do not produce a signal.
b) When touching the buttons, no buttons produce a signal.
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 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.
[11] K: SWITCH UNIT TEST
1. CARRY OUT 3D CHECKS.
2. Isolate the switch unit with the control panel frame to be tested.
3. Using an ohmmeter and referring to the switch unit matrix indicated on the switch unit circuit, check the circuit between the pins of the switch unit
that correspond to the STOP button. When the button is pressed, the ohmmeter should indicate short circuit. When the button is released, the
ohmmeter should indicate open circuit. If incorrect readings are obtained, the switch unitbutton is faulty and must be replaced. About the other but-
tons, the above method may be used.
4. CARRY OUT 4R CHECKS.
[12] L: RELAY (RY2, RY5, RY6) TEST
CARRY OUT 3D CHECKS.
Remove the outer case and check voltage between the pin No. 3 and No. 5 of connector CN-A on the control unit with an A.C. voltmeter. The meter
should indicate 230 volts, if not check oven circuit.
Relay Test
These relays are operated by D.C. voltage
G2H7(G3)G4H3H4
H5
(G9)
H6
(G7)
(G5)
AB
CSW100
C-1C-2C-3
B3 B2 B1A7
A6
A5
A4 A3
(G8)
(G10)
(C100)
(C101)
(R100)
(R101)
(c)
(b)
(b)
A2
A1
G6
(d)
(H8(G1))
(B4)
(c)
SW1
STOP
SW5
SW2
SW6
SW3
SW7
SW4
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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.
[13] M: PROCEDURES TO THE CONTROL UNIT
Problem: POWER ON, indicator does not light up.
CARRY OUT 3D CHECKS.
NOTE: At the time of these steps, make a visual inspection of the varistor for burned damage. And examine the transformer with a tester for the pres-
ence of layer short-circuit (check the primary coil resistance). If any abnormal condition is detected, replace the control unit.
CARRY OUT 4R CHECKS.
RELAY SYMBOL OPERATIONAL VOLTAGE CONNECTED COMPONENTS
RY5 Approx. 12.7V D.C. Oven lamp / Turntable motor / Cooling fan motor
RY2 Approx. 11.7V D.C. High voltage transformer
RY6 Approx. 12.7V D.C. Touch control transformer
STEPS OCCURRENCE CAUSE OR CORRECTION
1The rated AC voltage is not present between the Pin No. 3 and Pin No. 5
of connector CN-A. Check supply voltage and oven power cord.
2
The oven door is opened and closed.
But the rated AC voltage is not present to primary side of low voltage
transformer.
Check the secondary interlock switch.
If the secondary interlock switch is normal, the fuse or the
relay RY-6 is defective.
Check and replace the control unit.
3The rated AC voltage is present to primary side of low voltage trans-
former.
Low voltage transformer or secondary circuit defective.
Check and replace the control unit.

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it apart from the oven proper; in this case you must short
both ends of the door sensing switch (on PWB) of the touch
control panel with a jumper, which brings about an opera-
tional state that is equivalent to the oven door being closed.
As for the sensor-related controls of the touch control panel,
checking them is possible if the dummy resistor(s) with resis-
tance equal to that of the controls are used.
2. Servicing the touch control panel with power supply from an exter-
nal power source:
Disconnect the touch control panel completely from the oven
proper, and short both ends of the door sensing switch (on PWB) of
the touch control panel, which brings about an operational state
that is equivalent to the oven door being closed. Connect an exter-
nal power source to the power input terminal of the touch control
panel, then it is possible to check and repair the controls of the
touch control panel; it is also possible to check the sensor-related
controls of the touch control panel by using the dummy resistor(s).
3. Servicing Tools
Tools required to service the touch control panel assembly.
1) Soldering iron: 60W
(It is recommended to use a soldering iron with a grounding termi-
nal.)
2) Oscilloscope: Single beam, frequency range: DC - 10MHz type or
more advanced model.
3) Others: Hand tools
4. Other Precautions
1) Before turning on the power source of the control unit, remove the
aluminium foil applied for preventing static electricity.
2) Connect the connector of the key unit to the control unit being sure
that the lead wires are not twisted.
3) After aluminium foil is removed, be careful that abnormal voltage
due to static electricity etc. is not applied to the input or output ter-
minals.
4) Attach connectors, electrolytic capacitors, etc. to PWB, making
sure that all connections are tight.
5) Be sure to use specified components where high precision is
required.

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