DOWNLOAD Sharp R-33ST Service Manual ↓ Size: 787.09 KB | Pages: 28 in PDF or view online for FREE

R33ST - 3

12

13

14

1.

2.      

 keys

3.

 keys

4.

 key

5.

 keys

6.

 key

7.

 key

8.

 keys

9.

 key

10.

 key

11.

 key

12.

 key

13.

 button

1. Placed the roller stay on the floor of the oven
    cavity, engaging shaft into turntable motor shaft.
2. Then place the turntable on roller stay.

1.   Control panel
2.   Oven lamp
3.   Door open button
4.   Waveguide cover
5.   Coupling
6.   Oven cavity
7.   Door seals and sealing surfaces
8.   Door latchs
9.   Ventilation openings
10  Outer cabinet
11. Power supply cord
12. Turntable
13  Roller stay
14. Coupling

nfo

MICRO

Lbs Kg Oz AUTO

COOK

%

2

1

3

4

8

5

6

7

1

2

3

4

5

9

10

11

13

6
7

8

12

R33ST - 4

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor

RY1

Power transformer

RY3

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.

SETTING

32 sec. ON

24 sec. ON

18 sec. ON

12 sec. ON

6 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

HIGH

MEDIUM HIGH

MEDIUM

MEDIUM LOW

LOW

Approx. 70% = 630 Watts

100%

Approx. 50% = 450 Watts

Approx. 30% = 270 Watts

Approx. 10% = 90 Watts

 = 900 Watts

R33ST - 5

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
HEAD

DOOR

LATCH
HOOK

MONITOR
SWITCH
SW2

MONITORED
SWITCH
SW1

STOP
SWITCH
SW3

DOOR OPEN BUTTON

OPEN LEVER

R33ST - 6

NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL WHILE
THE OVEN IS IN OPERATION.

CARRY OUT 3D CHECKS.

Isolate the magnetron from high voltage circuit by removing all leads connected to filament terminal.

To test for an open circuit filament use an ohmmeter to make a continuity test between the magnetron
filament terminals, the meter should show a reading of less than 1 ohm.

To test for short filament to anode condition, connect ohmmeter between one of the filament terminals and
the case of the magnetron (ground). This test should be indicated an infinite resistance. If a low or zero
resistance reading is obtained then the magnetron should be replaced.

The following test procedure should be carried out with the microwave oven in a fully assembled condition
(outer case fitted). Microwave output power from the magnetron can be measured by way of IEC 705, i.e.
it is measured by how much power the water load can absorb. To measure the microwave output power in
the microwave oven, the relation of calorie and watt is used. When P(W) heating works for t (second),
approximately P x t/4.187 calorie is generated. On the other hand, if the temperature of the water with V(ml)
rises 

∆

T (

°

C) during this microwave heating period, the calorie of the water is V x 

∆

T.

The formula is as follows;

P x t / 4.187 = V x 

∆

 T

P (W) = 4.187 x V x 

∆

T / t

Our condition for water load is as follows:

Room temperature .............. around 20

°

C

Power supply Voltage ................. Rated voltage

Water load .................................... 1000 g

Initial temperature ................................. 10

±

2

°

C

Heating time ....................... 52+3=55 sec.
P = 80 x 

∆

T

Measuring condition:
1. Container

The water container must be a cylindrical borosilicate glass vessel having a maximum material thickness of
3 mm and an outside diameter of approximately 190 mm.

2. Temperature of the oven and vessel

The oven and the empty vessel are at ambient temperature prior to the start the test.

3. Temperature of the water

The initial temperature of the water is (10

±

2)

°

C.

4. Select the initial and final water temperature so that the maximum difference between the final water

temperature and the ambient temperature is 5K.

5. Select stirring devices and measuring instruments in order to minimize addition or removal of heat.
6. The graduation of the thermometer must be scaled by 0.1

°

C at minimum and be an accurate thermometer.

7. The water load must be (1000

±

5) g.

8. “t” is measured while the microwave generator is operating at full power. Magnetron filament heat-up time is

not included.

NOTE: The operation time of the microwave oven is “t + 3” sec. (3 sec. is magnetron filament heat-up time.)

Therefore total heating time = 55 sec.