R-90GCK (serv.man7). Test procedure - Sharp Home Appliance Service Manual (repair manual). Page 7

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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, troubleshooting by unit replacement is described
according to the symptoms indicated.
Before testing,

1) CARRY OUT 3D CHECKS.
2) Disconnect the leads to the primary of the high voltage transformer.
2) Ensure that these leads remain isolated from other components and oven chassis by using

insulation tape.

1.  Tact switch

NOTE ;
1) Reinstall the outer case (cabinet).
2) Reconnect the power supply cord after the outer case is installed.
3) Run the oven and check all functions.

The following symptoms indicate a defective tact switch.

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.
If the tact switch is defective.
1) CARRY OUT 3D CHECKS.
2) Replace the CPU unit.
3) CARRY OUT 4R CHECKS.

2. Control Unit

The following symptoms  indicate a defective control unit.  Before replacing the control unit,
perform the tact switch test (Procedure W) to determine if control unit is faulty. Reconnect the
power supply cord. And  check for followings.

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.
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 problems 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 measurment is not obtained.

When testing is completed, CARRY OUT 4R CHECKS.

1.

CARRY OUT 3D CHECKS.

2.  By using an ohmmeter, check the tact switch operation.
3. When the tact switch is not depressed, an ohmmeter should indicate an open circuit. When the

tact switch is depressed, an ohmmeter should indicate a short circuit. If improper operation is
indicated, the tact switch is probably defective and should be checked.

1. CARRY OUT 3D CHECKS.
2. Disconnect the leads to the primary of the high voltage transformer.
3. Ensure that these leads remain isolated from other components and oven chassis by using

insulation tape.

4. After that procedure, re-connect the power supply cord.