Sharp R-21AT Service Manual page 13

PROCEDURE
LETTER
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 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.
L KEY UNIT TEST
If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable
is marking good contact, verify that the door sensing switch (stop switch) operates properly; that is the
contacts are closed when the door is closed and open when the door is open. If the door sensing switch
(stop switch) is good, disconnect the flat ribbon cable that connects the key unit to the control unit and
make sure the door sensing switch is closed (either close the door or short the door sensing switch
connecter). 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 marking 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.
M RELAY TEST
CARRY OUT 3D CHECKS.
Remove the outer case and check voltage between Pin Nos. 3 and 7 of the 3 pin connector (A) 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.
DC. voltage indicated .......... Defective relay.
DC. voltage not indicated .... Check diode which is connected to the relay coil. If diode is good,
RELAY SYMBOL
RY2
RY3
CARRY OUT 4R CHECKS.
TEST PROCEDURES
G 1 G 2
G 9
G10
G11
G12
control unit is defective.
OPERATIONAL VOLTAGE
Approx. 18.0V D.C.
Approx. 18.0V D.C.
COMPONENT TEST
G 3 G 4 G 5
17
SELECT
7
POWER QUANTITY
18
SELECT EXPRESS
8
TIME DEFROST
19 15 13
9 5
20 16 14
0 6
CONNECTED COMPONENTS
High voltage transformer
Oven lamp / Antenna motor / Fan motor
11
G 6 G 7 G 8
DOUBLE
START SET
STOP/
CHECK
CLEAR
11
3 1
SIGNAL
12
4 2
R-21AT