Read Sharp R-27STMA (serv.man8) Service Manual online
R27STMA
8 – 4
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.
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 - 240 volts, if not check oven circuit.
should indicate 230 - 240 volts, if not check oven circuit.
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.
[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
1
The rated AC voltage is not present between the Pin No. 3 and Pin No. 5
of connector CN-A.
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.
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.
If the secondary interlock switch is normal, the fuse or the
relay RY-6 is defective.
Check and replace the control unit.
3
The rated AC voltage is present to primary side of low voltage trans-
former.
former.
Low voltage transformer or secondary circuit defective.
Check and replace the control unit.
Check and replace the control unit.
G2
H7(G3)
G4
H3
H4
H5
(G9)
H6
(G7)
(G5)
A
B
C SW100
C-1
C-2
C-3
B3
B2
B1
A7
A6
A5
A4
A3
(G8)
(G10)
< SW UNIT >
(C100)
(C101)
(R100)
(R101)
(c)
(b)
(a)
A2
A1
G6
WH-A
7pin HARNESS
WH-B
4pin HARNESS
WH-C
3pin WIRE HARNESS
(d)
(H8(G1))
(B4)
(a)
(b)
CHICKEN
QUARTERS
ROAST BEEF/
LAMB
START
AUTO MINUTE
AUTO
COOK
MEAT
JOINT
ROAST
POULITRY
POWER
LEVEL
ROAST
POAK
STOP
CEAR
WHOLE
POULTRY
(c)
SW1
SW2
SW3
SW4
SW5
SW6
SW7
SW8
SW9
SW10
