R-8740 (serv.man8). Test procedure - Sharp Home Appliance Service Manual (repair manual). Page 6

R-8740M  - 19

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlike conventional microwave ovens, proper maintenance can not 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 Key Unit,
and troubleshooting by unit 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.

a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) 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 M) to determine if control unit is faulty.

2-1  In connection with pads

a) When touching the pads, a certain group of pads do not produce a signal.
b) When touching the pads, no pads produce a signal.

2-2  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.

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.
d) Proper temperature measurement is not obtained.

CARRY OUT 3D CHECKS.
Remove the outer case and check voltage between Pin Nos. 11 and 9 of the 6 pin connector (A)  on the
control unit with an A.C. voltmeter.
The meter should indicate rated voltage, if not check oven circuit.

RY1, RY2, RY3, RY4, RY5 and RY7 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, grill cooking,
convection cooking or dual cooking.

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.

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

Approx. 24.0V D.C.

Oven lamp / Turntable motor

RY2

Approx. 18.0V D.C.

High voltage transformer

RY3

Approx. 23.0V D.C.

Top heating element

RY4

Approx. 23.0V D.C.

Bottom heating element

RY5

Approx. 23.0V D.C.

Fan motor

RY7

Approx. 23.0V D.C.

Convection motor

CARRY OUT 4R CHECKS.