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AND TEST PROCEDURE
AND ADJUSTMENT PROCEDURE
engineers with Operation and Service Information.
text of this manual, so they will be qualified to render satisfactory
energy which may radiate from the magnetron or other micro-
wave generating devices if it is improperly used or connected.
All input and output microwave connections, waveguides, flanges
and gaskets must be secured. Never operate the device without
a microwave energy absorbing load attached. Never look into
an open waveguide or antenna while the device is energized.
(A) The door is tightly closed.
(B) The door brackets and hinges are not defective.
(C) The door packing is not damaged.
(D) The door is not deformed or warped.
(E) There is not any other visible damage with the oven.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.
60 seconds after the oven has been switched off.
Wait for 60 seconds and then short-circuit the con-
nection of the high-voltage capacitor (that is, of the
connecting lead of the high-voltage rectifier) against
the chassis with the use of an insulated screwdriver.
carried out with the supply disconnected. It may in, some
cases, be necessary to connect the supply after the outer
case has been removed, in this event carry out 3D
checks and then disconnect the leads to the primary of
the high voltage transformer. Ensure that these leads
remain isolated from other components and the oven
chassis. (Use insulation tape if necessary.) When the
testing is completed carry out 3D checks and reconnect
the leads to the primary of the high voltage transformer.
3) Reconnect the supply.
4) Run the oven. Check all functions.
presence of microwave energy within a cavity, place a
cup of cold water on the oven turntable, close the door
and set the microwave timer for two (2) minutes. And set
the power level to HIGH (100%) and push the start key.
When the two minutes has elapsed (timer at zero)
carefully check that the water is now hot. If the water
remains cold carry out 3D checks and re-examine the
connections to the component being tested.
assembled, the microwave power output should be
checked and microwave leakage test should be carried
result in electrocution.
High voltage capacitor, High voltage transformer, Magnetron, High voltage rectifier , High voltage harness.
Single phase, 3 wire earthed
Operating frequency 2450 MHz
Timer (0 - 99 minutes and 90 seconds)
100P (HIGH) .......................... Full power throughout the cooking time
70P (MEDIUM HIGH) ............................... approx. 70% of Full Power
50P (MEDIUM) ......................................... approx. 50% of Full Power
30P (MEDIUM LOW) ................................ approx. 30% of Full Power
10P (LOW) ................................................ approx. 10% of Full Power
AUTO COOK pad, AUTO DEFROST pad
Weight pads, LESS/MORE pads
POWER LEVEL pad, STOP/CLEAR pad
START/AUTO MINUTE pad, TIMER pad
Weight conversion pads
AUTO START/CLOCK pad
5. Control panel
6. Rubber seal
7. Door latch openings
8. Oven cavity
9. Door seals and sealing surfaces
10.Safety door latches
13.Power supply cord
2. Door hinges
3. Waveguide cover
3 Roast Poultry
3 Minced Meat
2. TIME keys
3. INSTANT COOK keys
4. AUTO COOK key
5. AUTO DEFROST key
6. WEIGHT keys
7. LESS/MORE keys
8. POWER LEVEL key
9. STOP/CLEAR key
10. START/AUTO MINUTE key
11. TIMER key
12. AUTO START/CLOCK key
13. WEIGHT CONVERSION key
(monitored latch switch and stop switch).
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 noise filter and the control panel are
When the door is closed, the contacts (COM-NO) of the
monitored latch switch and the monitor switch are closed.
When the microwave power is set to 100P position by
pressing the power level pad and cooking time is entered
by touching the time pads, the following components are
energized: H.V. transformer, Magnetron, Oven lamp, Turn-
table motor and Fan motor.
and high voltage of approximately 2000 volts A.C. on
the secondary winding.
sent to the voltage doubling circuit, where it is doubled
to negative voltage of approximately 4000 volts D.C..
energy is channelled through the waveguide (transport
channel) into the oven cavity, where the food is placed
to be cooked.
monitored latch switch and stop switch are made open.
door, and monitors the operation of the monitored latch
switch and stop switch must open their contacts first.
After that the contacts (COM-NC) of the monitor
switch can be closed.
After that the contacts (COM-NO) of the monitored
latch switch (SW1) and stop switch (SW3) are closed.
remain closed, the fuse will blow, because the con-
tacts (COM-NC) of the monitor switch are closed and
a short circuit is caused.
power, the line voltage is supplied to the high voltage
transformer intermittently within a 32-seconds time base
through the relay contact which is coupled with the cur-
rent-limiting relay RY2. The following levels of microwave
power are given.
because approx. 3 seconds are needed for heat-
ing up the magnetron filament.
blows immediately after closing the contacts (COM-
NC) of the monitor switch.
AND MONITOR SWITCH FOR PROPER
OPERATION. (REFER TO CHAPTER “TEST
door open and when the contacts (COM-NC) of the
monitor switch are closes.
or fire hazard.
against overheating. If the temperature goes up higher
than 150˚C because the fan motor is interrupted or the
ventilation openings are blocked, the thermostat will cycle,
line voltage to the high voltage transformer will also cycle.
(If operated, check the magnetron for damage.)
is designed to prevent damage to the oven, if the food in
the oven catch fire due to over heating produced by
improper setting of cook time or failure of control unit.
Under normal operation, the thermal cut-out remains
closed. However, when abnormally high temperatures are
reached within the oven cavity, the thermal cut-out will
open at 125˚C, causing the oven to shut down. The
defective thermal cut-out must be replaced with a new
rotate the turntable.
This cool air is directed through the air vanes surrounding
the magnetron and cools the magnetron. This air is chan-
nelled through the oven cavity to remove steam and
vapours given off from heating food. It is then exhausted
through the exhaust vents at the rear of the oven cavity.
ference that might flow back into the power circuit.
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”
switch and monitor switch before replac-
ing the F1 fuse.
is plugged into wall outlet.
is plugged into wall outlet. (Timer
appear in display when power cord
is first plugged into wall outlet.
when Stop/Clear pad is touched.
(Buzzer should sound and " ; " or
time of day should appear in display.
stop when cooking time is 0 or
Stop/Clear pad is touched.
little or no heat is produced in oven
load. (Microwave power level is set
the variable cooking condition except
100% (HIGH) cooking condition.
shuts down before end of cooking
turntable motor do not operate at
the same time.
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.
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.
R.F. Power Output = (T2 - T1) x 70.
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/
Physical Laboratories are used.
filament winding of the high voltage transformer. It is very dangerous to work
near this part when the oven is on. NEVER make any voltage measurements
of the high-voltage circuits, including the magnetron filament.
Disconnect the leads to the primary winding of the high voltage transformer. Disconnect the filament
and secondary winding connections from the rest of the HV circuitry. Using an ohmmeter, set on a low
range, it is possible to check the continuity of all three winding. The following readings should be
b. Secondary winding .................... 140 ohms approximately
c. Filament winding ..................................... less than 1 ohm
and should be replaced.
CARRY OUT 4R CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be tested
using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal of the high
voltage rectifier and note the reading obtained. Reverse the meter leads and note this second reading.
The normal resistance is infinite in one direction and more than 100 k
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.
B. Continuity check must be carried out with measuring instrument which is set to the highest
E. An open capacitor constantly shows a resistance about 10 M
If incorrect reading are obtained, the high voltage capacitor must be replaced.
continuity test across the two terminals as described in the below.
Temperature of "OFF" condition (open circuit). ....................................................................... Above 125˚C
Indication of ohmmeter (When room temperature is approx. 20˚C.) ....................................... Closed circuit
may be due to over heating produced by improper setting of the cooking timer or failure of the control
Isolate the switch to be tested and using an ohmmeter check between the terminals
as described in the following table.