R-234 (serv.man2). Part 1 Text (1-28) - Sharp Home Appliance Service Manual (repair manual). Page 16

R-234 - 16

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 in one unit and troubleshooting by unit
replacement is described according to the symptoms indicated.
Control Panel.

The following symptoms indicate a defective control unit.

1.  Tact Switch.

The following symptoms indicate a defective tact switch. Replace the tact switch.

a) When touching a tact switch, a certain tact switch produces no signal at all.
b) When touching a tact switch, sometimes a tact switch produces no signal.

2. In connection with tact switches.

a) When touching a tact switch, a certain group of tact switch do not produce a signal.
b) When touching a tact switch, no tact switch produce a signal.

3. Display problems.

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.
h)  When touching a tact switch, the control unit does not respond.

4. Other possible problems caused by defective control unit.

a) Buzzer does not sound or continues to sound.
b) Cooking is not possible.

Do not touch the electrical parts and the printed wiring board to prevent an electric

shock. Because the control unit is " TRANSLESS CIRCUIT " and all electrical parts
are used at A.C. line voltage.

CARRY OUT 3D CHECKS.

Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two
terminals as described in the table below.

Table: Resistance of Motor

Motors

Resistance

Fan motor

Approximately 360 

Ω

Turntable motor

Approximately 12 - 15 k

Ω

If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS.

1. CARRY OUT 3D CHECKS.
2. Disconnect the leads from the primary of the high voltage transformer. Make sure that the leads

remain isolated from other oven components and chassis (Use insulation tape if necessary.)

3. Connect the voltmeter, set to 250V AC, across the motor terminals. (Refer to the relevant motor test

procedure or pictorial diagram for the correct terminal numbers.)

4. Arrange the meter in a position where it can be read during the test.

(Do not touch the meter, meter leads or oven circuitry while the oven is active.)

5. Close the oven door.
6. Set  the power level to 800W and set the relevant timer for about three (3) minute.
7. Note the reading on the meter and carefully observe the motor under test to see if it is turning.
8. CARRY OUT 3D CHECKS.
9. Remove the test meter leads.
10. Reconnect the leads to the primary of the high voltage transformer.

If a reading of the line voltage was obtained (step 7) but the motor was not turning then it is faulty and
should be replaced. If the meter indicated that the no supply was present then the winding to the motor
should be checked for continuity.