Sharp R-880B Service Manual page 19

PROCEDURE
LETTER
N 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.
O RELAY TEST
CARRY OUT 3D CHECKS.
Remove the outer case and check voltage between Pin No. 1 of the 3 pin connector (A) and the
common terminal of the relay RY6 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 mix 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
RY1
RY2
RY3
RY4
RY5
RY6
CARRY OUT 4R CHECKS.
P PROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE PRINTED WIRING BOARD
(PWB) IS OPEN
To protect the electronic circuits, this model is provided with a fine foil pattern added to the input circuit
on the PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the troubleshooting guide
given below for repair.
Problem: POWER ON, indicator does not light up.
CARRY OUT 3D CHECKS.
TEST PROCEDURES
COMPONENT TEST
G 8 G 7 G 6
5 3
4
160˚C 150˚C 130˚C
0 9 8
250˚C 230˚C 220˚C
INSTANT
COOK/
Pasta
MORE
START
CONVEC CLOCK PREHEAT
control unit is defective.
OPERATIONAL VOLTAGE
Approx. 24.0V D.C.
Approx. 24.0V D.C.
Approx. 24.0V D.C.
Approx. 24.0V D.C.
Approx. 24.0V D.C.
Approx. 24.0V D.C.
17
G 5 G 4 G 3
2 1
EASY
DEFROST
70˚C 40˚C
7 6
REHEAT
SENSOR
Vegetables
200˚C 180˚C
POWER
Jacket
Rice
LEVEL Vegetables
Potato
Reheat
GRILL
Pie
LESS
CONNECTED COMPONENTS
Convection motor
High voltage transformer
Grill heaters (Top)
Bottom heater
Fan motor
Oven lamp / Turntable motor
R-880B
G 2 G 1
MULTI
HELP
COOK
STOP/
Fresh
CLEAR
Frozen CONVENIENCE
/PIZZA
MIX