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R32STM - 5

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor

RY1

Power transformer

RY3

Approx. 10% = 90 Watts

32 sec. ON

6 sec. ON

12 sec. ON

18 sec. ON

24 sec. ON

30 sec. OFF

20 sec. OFF

14 sec. OFF

8 sec. OFF

LOW

MEDIUM HIGH

MEDIUM

MEDIUM LOW

HIGH

Approx. 70% = 630 Watts

Approx. 50% = 450 Watts

Approx. 30% = 270 Watts

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

IMPORTANT
When the oven door is closed, the monitor switch contacts
COM - NC must be open.
When the microwave oven is plugged in a wall outlet (230
-240V 50Hz), the line voltage is supplied to the point A3+A5
in the control unit.

1. The display flashes ”88:88”.
2. To set any programmes or set the clock, you must first

touch the STOP pad.

3. “  :  ” appears in the display.

Enter a desired cooking time by touching the Time pads and
start the oven by touching the START pad.

1. The line voltage is supplied to the primary winding of the

power transformer. The voltage is converted to about
3.3 volts A.C. output on the filament winding and high
voltage of approximately 2000 volts A.C. on the
secondary winding.

2. The filament winding voltage (3.3 volts) heats the

magnetron filament and the high voltage (2000 volts) is
sent to the voltage doubling circuit, where it is doubled
to negative voltage of approximately 4000 volts D.C..

3. The 2450 MHz microwave energy produced in the

magnetron generates a wave length of 12.24 cm. This
energy is channelled through the waveguide (transport
channel) into the oven cavity, where the food is placed
to be cooked.

4. When the cooking time is up, a single tone is heard and

the relays RY1 + RY3 go back to their home position.
The circuits to the oven lamp, power transformer, fan
motor and turntable motor are cut off.

5. When the door is opened during a cook cycle, the

switches come to the following condition.

The circuits to the power transformer, oven lamp fan
motor and turntable motor are cut off when the monitored
latch switch and stop switch are made open.   Shown in
the display is the remaining time.

6. MONITOR SWITCH CIRCUIT

The monitor switch (SW2) is mechanically controlled by
oven door, and monitors the operation of the monitored
latch switch (SW1)

6-1

When the oven door is opened during or after the
cycle of cooking program, the monitored latch switch
(SW1), and stop switch (SW3) must open their contacts
first. After that the contacts (COM - NC) of the monitor
switch (SW2) can be closed.

6-2

When the oven door is closed, the contacts
(COM - NC) of the monitor switch (SW2) must be
opened first.  After that the contacts of the monitored
latch switch (SW1) and stop switch (SW3) are closed.

6-3

When the oven door is opened and the contacts of the
monitored latch switch (SW1) remain closed, the fuse
(F1) F8A will blow, because the monitor switch is
closed and a short circuit is caused.

When the microwave oven is preset for variable cooking
power, the line voltage is supplied to the power 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 microwave power are given.

CONDITION

DURING

DOOR OPEN

SWITCH

CONTACT

COOKING

(NO COOKING)

Monitored latch switch

COM-NO

Closed

Open

Monitor switch

COM-NC

Open

Closed

Stop switch

COM-NO

Closed

Open

Monitor switch

COM-NO

Closed

Open

NOTE: The ON/OFF time ratio does not exactly correspond

to the percentage of microwave power, because
approx. 3 seconds are needed for heating up the
magnetron filament.

100% = 900 Watts

SETTING

R32STM - 6

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) must be opened.

f the oven door is opened and the contacts

(COM-NO) of the monitored latch switch SW1
fail to open, the fuse F1 blows simultaneously
with closing the contacts (COM-NC) of the
monitor switch SW2.

CAUTION:  BEFORE REPLACING A BLOWN

FUSE F1 TEST THE MONITORED
LATCH SWITCH SW1, MONITOR
SWITCH SW2.

Ensure the following:

1. Wires must not touch:

a) High voltage parts.
    (Magnetron, high voltage transformer, high voltage capacitor and high voltage rectifier assembly)
b) Parts that become hot.
    (Heating elements, oven lamp, oven cavity magnetron and high voltage transformer)
c) Sharp edges.
    (Bottom plates, oven cavity, waveguide flange, chassis support and other metallic parts)
d) Movable parts.
    (Fan blade, any motor, switch, switch lever and open button)

2. Positive lock connectors are fitted correctly.
3. Wires are connected correctly as per pictoral diagram.
4. No wire leads are trapped by the outer wrap.

Before carrying out any work; carry out 3D checks.
1.

isconnect the supply.

2.

oor opened, and wedged open.

3.

ischarge the high voltage capacitor.

LATCH
HEADS

LATCH HOOK

MONITOR
SWITCH (SW2)

MONITORED
LATCH
SWITCH (SW1)

STOP
SWITCH
(SW3)

DOOR OPEN BUTTON

OPEN LEVER

DOOR

R32STM - 7

A

MICROWAVE OUTPUT POWER

The power output of this oven is rated using the method specified by IEC-705.  Full
details of how to carry out this procedure can be found in the Sharp Technical Training
notes which is available from Sharp Parts Centre (part number SERV-LITMW01).

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-705 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 70.

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

R32STM - 8

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 Key  Unit, and also the control unit is divided into two units, CPU Unit and Power Unit, and
troubleshooting by unit replacement is described according to the symptoms indicated.
1.  Key Unit

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

2.  Control Unit

The following symptoms indicate a defective control unit. Replacing the control unit.

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.

If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon
cable is making good contact, verify that the door sensing switch (stop switch) operates properly;
that is the contacts are closed when the door is closed and open when the door is open. If the
door sensing switch (stop switch) is good, disconnect the flat ribbon cable that connects the key
unit to the control unit and make sure the door sensing switch is closed (either close the door
or short the door sensing switch connecter). Use the Key unit matrix indicated on the STOP/
CLEAR pad making momentary contact. If the control unit responds by clearing with a beep the
key unit is faulty and must be replaced. If the control unit does not respond, it is a faulty and must
be replaced. If a specific pad does not respond, the above method may be used (after clearing
the control unit) to determine if the control unit or key pad is at fault.

G11

G7

G2

G5. 9

G12

G10

G8

G6

G4

G3

G1

10 min.

10 sec.

1 min.

TIMER

Kg / Lb

g 

• oz

Kg 

• Lb

LESS

MORE

STOP/

CLEAR

AUTO

COOK

POWER

LEVEL

RICE/

PASTA

CAKE

FRESH

VEG.

FRESH

FISH

MINCED

MEAT

SPONGE

PUDDING

CANNED

FOOD

AUTO

DEFROST

JACKET

POTATOES

START

CLOCK

AUTO

MINUTE

AUTO START