R-21FBSTM - Sharp Home Appliance Service Manual (repair manual). Page 13

R-21FBSTM/R-22FBSTM - 13

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 three units,Control unit,Switch Unit,  and
LED Unit. Troubleshooting by unit replacement is described according to the symptoms indicated.
Control Panel.

The following symptoms indicate a defective control unit.

1.  Switch Unit.

NOTE: Check switch unit lead wire harness connection before replacement.

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

a) When touching the keys, a certain key produces no signal at all.
b) When touching a key,two figures or more are displayed.
c) When touching the keys,sometimes a key produces no signal.

2. Control Unit

The following symptoms indicate a defective control unit. Replace the control unit, perform the switch
 unit test(Procedure L) to determine if control unit is faulty.

2-1In connection with keys.

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

2-2.In connection with indicators.

a) At a certain digit, all or some dots do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light up.
d) The corresponding dots 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.

2-3.Other possible problems caused by defective control unit.

a) Buzzer does not sound or continues to sound.
b) Clock does not operate prperly.
c) Cooking is not possible.

3.

LED Unit
a) No backlight behind display.
b) Dull backlight behind display.

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 290 

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) minutes.
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 or other circuit checks should be made, i.e. relays,switches.