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R-64STM -5

Closing the door activates all door interlock switches
(Monitored latch switch, and stop switch.)

When the microwave oven is preset for variable cooking
power, the 240 volts is supplied to the high voltage
transformer intermittently within a 32-second time base
through the relay contact which is coupled with the
current-limiting relay RY3. The following levels of micro-
wave power are given.

32 sec. ON

24 sec. ON

18 sec. ON

12 sec. ON

6 sec. ON

8.0 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

HIGH

MEDIUM 
HIGH

MEDIUM

MEDIUM 
LOW

LOW

Approx. 70%

Approx. 50%

Approx. 30%

Approx. 10%

100%

Note:

The On/Off time ratio does not exactly corre-
spond to the percentage of microwave power,
because  approx. 2 seconds  are needed for
heating up the magnetron filament.

SETTING

The door can be opened by pulling the door.

Figure D-1. Door Open Mechanism

1. When the oven door is closed, the contacts (COM-

NO) must be closed.

2. When the oven door is opened, the contacts (COM-

NO) of each switch must be opened.

1. When the oven door is closed, the contacts (COM-

NC) must be opened.

2. When the oven door is opened, the contacts (COM-

NC) must be closed.

3. If the oven door is opened and the contacts (COM-

NO) of the monitored latch switch (SW1) fail to open,
the fuse F1 blows immediately after closing the con-

1. If the wire harness or electrical components are

short-circuited, this fuse blows to prevent an electric
shock or fire hazard.

2. The fuse also blows when monitored latch switch

remains closed with the oven door open and when
the monitor switch contact (COM-NC) closes.

3. The fuse also blows when the H.V. rectifier, H.V. wire

harness, H.V. capacitor, magnetron or secondary
winding of high voltage transformer is shorted.

The thermal cut-out protects the oven against the over
heat during grill cooking or combi grill cooking. If the
temperature rises above 145˚C because the fan motor
is interrupted, the air inlet duct is blocked or the ventila-
tion openings are obstructed, the thermal cut-out opens
and switches off the all electrical parts. The defective
thermal cut-out  makes the contact by cooling down.

This thermal cut-out protects the high voltage trans-
former against overheating. If the temperature goes up
higher than 150˚C because the fan motor is interrupted
or the ventilation openings are blocked, the thermal cut-
out  will open and line voltage to the high voltage
transformer will cut off and operation of the magnetron
will be stopped.  The defective thermal cut-out makes
the contact by cooling down.

tacts (COM-NC) of the monitor switch (SW2).

CAUTION: BEFORE REPLACING A BLOWN FUSE  F1

TEST MONITORED LATCH SWITCH (SW1)
AND  MONITOR SWITCH (SW2) FOR
PROPER OPERATION.  (REFER TO CHAP-
TER “TEST PROCEDURE”).

Latch hook

SW3: Stop switch

Door

SW2: Monitor switch

SW1:Monitored latch switch

Latch heads

R-64STM -6

MICROWAVE OUTPUT POWER

The power output of this oven is rated using the method specified by IEC-60705.
Full details of how to carry out thisprocedure can be found in the Sharp Technical Training notes which is
available 

     from Sharp Parts Centre (part number SERV-LITMW01).

The IEC-60705 procedure must be carried out using laboratory-type procedures and equipment.
These requirements make the procedure unsuitable for routine performance checks.

Note:

The following test method gives an indication of the output power only, it cannot be used to establish
the actual/rated output power.  If the true output power is required, then the IEC-60705 test method
must be used.

Alternative simplified method:
1. Place 2 litres of cold water (between 12

°C and 20°C) in a suitable container.

2. Stir the water and measure the temperature in 

°C.  Note temperature as T1.

3. Place the container in the microwave and heat the water for 2 minutes on full power.
4. When the 2 minutes is completed, remove the container and stir the water.  Note the water temperature as T2.
5. Calculate the output power using the following formula:

R.F. Power Output = (T2 - T1) x 80.

MICROWAVE LEAKAGE TEST

This oven should be tested for microwave leakage on completion of any repair or adjustment, following the
procedure described in the Sharp Technical Training notes (part number SERV-LITMW01).  The maximum
leakage permitted in BS EN 60335-2-25 is 50W/m

2 

(equivalent to 5mW/cm

2

), however it is not normal to

detect any significant leakage, therefore, any leakage which is detected should be investigated.

It is essential that only leakage detectors with current calibration traceable to the National Physical Laboratories
are used.

Suitable leakage detectors :

CELTEC A100
APOLLO X1

R-64STM -7

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, the touch control panel assembly is divided into two units, Control Unit and
Switch  Unit, and troubleshooting by unit replacement is described according to the symptoms
indicated.
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. Before replacing the control unit,
perform the Switch unit test (Procedure L) to determine if control unit is faulty.

2-1  In connection with keys.

a) When touching the keys, a certain group of keys do not produce a signal.
b) When touching the 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.
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.

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.

If the display fails to clear when the STOP/
CLEAR key is depressed, first verify the lead
wire harness is making good contact, verify that
the stop switch operates properly; that is the
contacts are closed when the door is closed
and open when the door is open. If the stop
switch is good, disconnect the lead wire har-
ness that connects the switch unit to the main
board and make sure the stop switch is closed
(either close the door or short the stop switch
connector). Use the Switch unit matrix indi-
cated on the switch unit circuit and place a
jumper wire between the pins that correspond
to the STOP/CLEAR key making momentary
contact. If the is assembly responds by clearing
with a beep the switch unit is faulty and must be
replaced. If the assembly does not respond,
the main board faulty and must be replaced. If
a specific key does not respond, the above
method may be used (after clearing the display
) to determine if the main board or switch unit is
at fault.

1

2

3

4

SW2

5

6

SW3

SW4

SW5

SW6

SW7

CN-G

SW1

START / AUTO MINUTE

X1 MICRO
X2 GRILL
X3 DUAL GRILL

MEAT JOINT

MINCED MEAT

Express Cook 

WHOLE POULTRY

STOP / CLEAR

R-64STM -8

Remove the outer case and check voltage between Pin No. 1 and Pin No. 3 of the 3 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 and RY3 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, dual
grill cooking operation, or grill 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. 24.0V D.C.

Oven lamp / Turntable motor / Cooling fan motor

RY2

Approx. 18.0V D.C.

Heating element

RY3

Approx. 18.0V D.C.

High voltage transformer

To protect the electronic circuits, this model is provided with a fine foil pattern added to the primary
on the PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the troubleshooting guide
given below for repair.
Problem: POWER ON, indicator does not light up.
CARRY OUT 3D CHECKS.

STEPS

OCCURRENCE

CAUSE OR CORRECTION

1

The rated AC voltage is not present at

Check supply voltage and oven power cord.

POWER terminal of CPU connector (CN-A).

2

The rated AC voltage is present at primary

Low voltage transformer or secondary circuit defective.

side of low voltage transformer.

Check and repair.

3

Only pattern at "a" is broken.

*Insert jumper wire J1 and solder.

(CARRY OUT 3D CHECKS BEFORE REPAIR)

4

Pattern at "a" and "b" are broken.

*Insert the coil RCILF2003YAZZ between "c" and "d".

(CARRY OUT 3D CHECKS BEFORE REPAIR)

NOTE: *At the time of these repairs, make a

visual inspection of the varistor for burn-
ing damage and examine the transformer
with tester for the presence of layer short-
circuit (check primary coil resistance). If
any abnormal condition is detected, re-
place the defective parts.

CARRY OUT 4R CHECKS.

RY2

OL / FM
/ TTM

AC

5

1

D20 

VRS1

CN - A

D21 

RY1

(J1)

T1