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R-82FBSTM - 10

D2

D1

ASYMMETRIC
RECTIFIER

HIGH VOLTAGE 
RECTIFIER

A

B

C

The door can be opened by pulling the door handle. When
the handle is pulled, the latch head is pulled, the latch head
is moved upward, and released from the latch hook now
the door can be opened.

1. When the oven door is closed, the contacts (COM-NO)

of the switch must be closed. The contacts (COM-NC) must
be opened.

2. When the oven door is opened, the contacts (COM-NO) of

the switch must be opened. The contacts (COM-NC) must be
closed.

1. When the oven door is closed, the contacts (COM-NO) of the

switch must be closed.

2. When the oven door is opened, the contacts (COM-NO) of

switch must be opened.

The monitor switch is activated (the contacts opened) by the upper
latch head on the door while the door is closed. The switch is
intended to render the oven inoperative by means of blowing the
fuse F8A when the contacts of the monitored latch switch fail to open
when the door is opened.
Function
1. When the door is opened, the contacts (COM-NC) of monitor

switch  close (to the ON condition) due to their being normally
closed and contacts (COM-NO) open. At this time the con-
tacts (COM-NO) of monitored latch switch is in the OFF
condition (contacts open) due to their being normally open
contact switches.

2. As the door goes closed, the monitor switch contacts (COM-

NC) are opened and contacts (COM-NO) are closed. The
contacts (COM-NO) of monitored latch switch and stop switch
are closed.(On opening the door, each of these switches
operate inversely.)

3. If the door is opened and the monitored latch switch  con-

tacts  (COM-NO) fail to open, the fuse F8A blows immedi-
ately after closing of the monitor switch (COM-NC) contacts.

CAUTION: BEFORE REPLACING A BLOWN FUSE F8A,

TEST THE MONITORED LATCH SWITCH AND
MONITOR SWITCH FOR PROPER OPERATION.
(REFER TO CHAPTER “TEST PROCEDURE”)

If the wire harness or electrical components are short-circuited,
this fuse blows to prevent an electric shock or fire hazard.

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 the 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 asymmetric rectifier, H.V.

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

T/C transformer converts A.C. line voltage into low voltage to
drive the control unit.

This thermal cut-out protects the magnetron against overheat.
If the temperature goes up higher than 125˚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 must be replaced with a
new one.

This thermal cut-out protects against overheating or fire inside the
oven. If the temperature rises above 160˚C the thermal  cut-out
opens, the oven will switch off.The defective thermal cut-out must
be replaced with a new one.

T

he asymmetric rectifier is solid state device that prevents

current flow in both directions. It prevents the temperature rise of
the high voltage transformer by blowing the fuse F8A when the
high voltage rectifier is shorted.

The rated peak reverse voltage of D1 of the asymmetric
r

ectifier is 6 KV. The rated peak reverse voltage of D2 of the

asymmetric rectifier is 1.7 KV. D1 and D2 of the
asymmetric rectifier or high voltage rectifier are shorted when the
each peak reverse voltage goes beyond the each rated peak
reverse voltage. (The process of the blowing the fuse F8A.)
1. The high voltage rectifier is shorted by some fault when

microwave cooking or dual cooking.

2. The peak reverse voltage of D2 of the rectifier goes beyond

the rated peak reverse voltage 1.7 KV in the voltage doubler
circuit.

3. D2 of the rectifier is shorted.
4. The large electric currents flow through the high voltage

winding of the high voltage transformer.

5. The large electric currents beyond 8A flow through the

primary winding of the high voltage transformer.

6. The fuse F8A blows by the large electric currents.
7. The power supplying to the high voltage transformer is cut off.

Latch hook

Door

SW2: Stop switch

Latch
Heads

SW3: Monitor switch

SW1: Monitored

latch switch

Tab

R-82FBSTM - 11

The turntable motor rotates the turntable.

The fan motor drives a blade which draws external cool air, this
cool air is directed through the air vanes surrounding the
magnetron and cools the magnetron. Air is channelled through
the oven cavity to remove steam and vapours given off from
heating food. It is then exhausted through the air vents of the
oven cavity.

The convection motor drives the convection fan and provide the
heated air.

The grill heating element is provided to brown the food and is
located on the top of the oven cavity.

The grill heating element is provided to brown the food and is
located at the base of the oven cavity.

This oven is designed with a hot air heating system where food
is heated by forced circulation of the hot air produced by the grill
heaters.  The air heated by the grill heating elements is circulated
through the convectin passage provided on the outer casing of
the oven cavity by means of the convection fan which is driven
by the convection motor.  It then enters the inside of the oven
through the  vent holes provided on the back of the oven. Next,
the hot air heats the food on the turntable and leaves the oven
cavity through the vent in the oven cavity rear wall.  In this way,
the hot air ciculates inside the oven cavity to raise its temperature
and at the same time, comes into contact with the food cooked.
When the temperature inside the oven cavity reaches the
selected temperature, the heating elements are de-energized.
When the temperature inside the oven cavity drops below the
selected temperature, the elements are energized again.  In this
way, the inside of the oven is maintained at approximately the
selected temperature.  When the convection time reaches "0",
the heating elements are de-energzed and the convection fan
stops operating and the oven shuts off.  At that time if the cavity
air temperature has risen above 120˚C, the fan remains rotating.
Automatically the fan motor will shut down at low temperature
(less than 105˚C).

The oven will stop its operation when there is a fire in the
oven cavity in microwave cooking condition.
LSI measures the voltage across the temperature meas-
urement circuit intermittently within 32-seconds time base
since the oven is started in microwave cooking condition.
The oven will stop its operation when the difference of the
voltage is more than 0.781 volts in microwave cooking
condition.

1. Within a 32-seconds base, the thermistor is energized

for 2 seconds.  At that time, the voltage across the
temperature measurement circuit is measured.

2. The oven carries out the procedure above again. If the

second voltage is 0.781V higher than first voltage, LSI
judges that there is a fire in the oven cavity and stops
the oven.

3. When LSI judges that there  is a fire in the oven cavity,

LSI will switch off the relays to high voltage transformer,
fan motor and LSI stops counting down.

1. If the temperature of the thermistor does not rise to more than

40˚C after 4 minutes and 15 seconds from when the oven is
started in oven cooking mode, dual cooking mode or grill (top
and bottom) cooking mode, the oven is turned off.

2. When the thermistor or the wire harness to the thermistor is

opened, the oven is turned off after 4 minutes and 15 seconds
because this condition is same as above

THERMISTOR

SENSING

VOLTAGE

ON

OFF

ON

OFF

30

32 (sec.)

Sensing the voltage across temperature measurement circuit.

Door

Oven Cavity

Grill Heating
Element

Bottom Grill 
Heating Element

Convection
Passage

Cooling
Fan

Convection
Motor

Convection
Fan

Turntable

Insulation

Turntable
Motor

The noise filter assembly prevents radio frequency interference
that might flow back in the power circuit.

R-82FBSTM - 12

When troubleshooting the microwave oven, it is helpful to
follow the Sequence of Operation in performing the checks.
Many of the possible causes of trouble will require that a
specific test be performed. These tests are given a proce-
dure letter which will be found in the “Test Procedure”
section.

IMPORTANT: If the oven becomes inoperative because

of a blown fuse F1. Check the monitored
latch switch and monitor switch before
replacing the F8A fuse.

Fuse F2 F8A blows when the door is opened.

Home fuse blows when power cord is plugged into wall outlet.

Fuse F1 20A blows when power cord is plugged into wall outlet.

Nothing appears in display when power cord is plugged into wall ou

tlet 

and the door is opened and closed.

Display does not operate properly when STOP button is pressed.

Oven lamp does not light when door is opened. (Display operates.)

Oven does not start when the START 

button is pressed.

 (Display operates.)

Oven lamp does not light  and turntable motor does not operate.

Fan motor does not operate. (Oven lamp lights.)

Convection fan motor does not operate. (Oven lamp lights.)

Turntable motor does not operate. (Oven lamp lights.)

Oven or any electrical parts (except fan motor) does not stop when 

cooking time is 0 or STOP  button is pressed.

Oven stops after 4 minutes and 15 seconds since START kbutton is 

pressed. (Except Microwave and Dual Cook modes)

Display operates properly but all electrical parts do not operate.

Oven goes into cook cycle but shuts down before end of cooking cycle.

After cooking, the temperature of oven cavity is higher than 105˚C but 

fan motor does not operate.

Oven seems to be operating but little or no heat is produced in oven 

load. (Microwave power control is set at HIGH)

Oven does not seem to be operating properly during variable cooking 

condition except HIGH cooking condition.

Oven goes into cook cycle but shuts down before end of cooking cycle.

Convection cooking mode does not heat.

Oven seems to be operating but the temperature in the oven cavity is 

lower or higher than preset one. 

Grill heating element does operate.

Oven goes into cook cycle but shuts down before end of cooking cycle.

Oven seems to be operating but little or no heat is produced in oven 

load. (Microwave power does not seem to be generated properly)

Oven seems to be operating but the temperature in the oven cavity is 

lower or higher than preset one. 

Top and Bottom Grill heating elements do not heat.

Top or Bottom Grill heating element does not heat.

OFF

CONDITION

COOKING

CONDITION

(COMMON MODE)

MICROWAVE

COOKING

CONDITION

GRILL COOKING

CONDITION

CONVECTION

COOKING

CONDITION

DUAL COOKING

CONDITION

(COMMON MODE)

DUAL COOKING

CONDITION

(MICRO./CONV.)

DUAL COOKING

CONDITION

(MICRO./GRILL)

CONDITION 

PROBLEM

BLOCKED COOLING FAN

BLOCKED CONVECTION FAN

NO POWER AT WALL OUTLET

HOME FUSE OR BREAKER

MIS-ADJUSTMENT OF SWITCHES

BLOCKED VENTILATION OPENINGS

OPENED WIRE HARNESS

SHORTED WIRE HARNESS

OVEN LAMP OR SOCKET

POWER SUPPLY CORD

FOIL PATTERN ON P.W.B.

RELAY RY7

RELAY RY6

RELAY RY5

RELAY RY4

RELAY RY3

RELAY RY2

RELAY RY1

KEY/JOG UNIT

CONTROL PANEL

TC TRANSFORMER

BOTTOM GRILL HEATING ELEMENT

TOP GRILL HEATING ELEMENT

FUSE F8A F2

FUSE 20A F1

NOISE FILTER

CONVECTION FAN MOTOR

FAN MOTOR

TURNTABLE MOTOR

THERMAL CUT-OUT 160˚C TC2

THERMAL CUT-OUT 125˚C TC1 

THERMISTOR

MONITOR SWITCH SW3

STOP SWITCH SW2

MONITORED LATCH SWITCH SW1

HIGH VOLTAGE CAPACITOR

H.V. HARNESS

H.V. RECTIFIER ASSEMBLY

HIGH VOLTAGE  TRANSFORMER

MAGNETRON

AB

C

D

EEE

F

G

G

H

H

H

I

J

K

L

L

M

N

O

O

O

O

O

O

O

P

TEST PROCEDURE

POSSIBLE CAUSE

AND

DEFECTIVE PARTS

R-82FBSTM - 13

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 power output of this oven is rated using the method specified by  IEC 60705. 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).

The IEC-60705 procedure must be carried out using laboratory-type procedures and equip-
ment.
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 IEC705
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 1 minute and 36 seconds on full power.

NOTE: The operation time of the microwave oven includes "3" sec. (3 sec. is magnetron filament

heat-up time.)

4. When the 1 minute and 36 seconds is completed, remove the  container and stir the water. Note

temperature as T2.

5. Calculate the output power using the following formula:

R.F. Power Output = (T2 - T1) x 90.

±

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 National Physical
Laboratories are used.

Suitable leakage detectors: CELTEC A100

APOLLO X1

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