R-341AM - Sharp Home Appliance Service Manual (repair manual). Page 6

R341M - 6

Remove the outer case and check voltage between Pin No 5 of the 3 pin connector (A) and common terminal
of the relay (RY2) on the control unit with an A.C. voltmeter.
The meter should indicate rated voltage, if not check oven circuit.

RY1 and RY2 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.

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. 19.0V D.C.

Oven lamp / Turntable motor / Cooling fan motor

RY2

Approx.   7.5V D.C.

Power transformer

To prevent an electric shock. Do not touch the electrical parts and the printed wiring
board. Because the control unit is " TRANSLESS CIRCUIT " and all electrical parts
are used at A.C. line voltage.

              C              RELAY TEST

1. Disconnect the oven from the power supply.
2. Discharge the high voltage capacitor.
3. Remove the control unit from the control panel.
4. By using an ohmmeter, check the tact switch operation.
5. 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.

              B              TACT SWITCH TEST

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.