R-252M (serv.man2) - Sharp Home Appliance Service Manual (repair manual)

Model
R-252M (serv.man2)
Pages
35
Size
527.42 KB
Type
PDF
Document
Service Manual
Brand
Device
Home Appliance / Microwave Oven
File
r-252m-sm2.pdf
Date

View Sharp R-252M (serv.man2) Service Manual online

R-252M   1
SERVICING
PRODUCT SPECIFICATIONS
GENERAL INFORMATION
APPEARANCE VIEW
OPERATING SEQUENCE
FUNCTION OF IMPORTANT
COMPONENTS
TROUBLESHOOTING GUIDE
AND TEST PROCEDURE
TOUCH CONTROL PANEL
COMPONENT REPLACEMENT
AND ADJUSTMENT PROCEDURE
MICROWAVE MEASUREMENT
WIRING DIAGRAM
PARTS LIST
SHARP CORPORATION
OSAKA, JAPAN
SERVICE MANUAL
MICROWAVE OVEN
  R-252(B)M/ R-252(BL)M/ R-252(G)M/ R-252(W)M/ R-252(SL)M
GENERAL IMPORTANT INFORMATION
This Manual has been prepared to provide Sharp Corp. Service
engineers with Operation and Service Information.
It is recommended that service engineers carefully study the entire
text of this manual, so they will be qualified to render satisfactory
customer service.
CAUTION
MICROWAVE RADIATION
Service engineers should not be exposed to the microwave
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.
WARNING
Never operate the oven until the following points are ensured.
(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.
Servicing and repair work must be carried out only by trained
service engineers.
All the parts marked "*" on parts list are used at voltages more than
250V.
Removal of the outer wrap gives access to potentials above 250V.
All the parts marked "
" on parts list may cause undue microwave
exposure, by themselves, or when they are damaged, loosened or
removed.
R-252M   2
REMEMBER TO CHECK 3D
1) Disconnect the supply.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.
WARNING: AGAINST THE CHARGE OF THE
HIGH-VOLTAGE CAPACITOR.
The high-voltage capacitor remains charged about
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.
Sharp recommend that wherever possible fault-finding is
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.
REMEMBER TO CHECK 4R
1) Reconnect all leads removed from components dur-
ing testing.
2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run the oven. Check all functions.
Microwave ovens should not be run empty. To test for the
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.
When all service work is completed and the oven is fully
assembled, the microwave power output should be
checked and microwave leakage test should be carried
out.
 SERVICING
 WARNING TO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of producing very high voltage and current. Contact with following parts will
result in electrocution.
High voltage capacitor, High voltage transformer, Magnetron, High voltage rectifier , High voltage harness.
R-252M   3
  GENERAL INFORMATION
WARNING
THIS APPLIANCE MUST BE EARTHED
IMPORTANT
THE WIRES IN THIS MAINS LEAD ARE COLOURED IN ACCORDANCE WITH THE FOLLOWING CODE:
GREEN-AND-YELLOW
: EARTH
BLUE
: NEUTRAL
BROWN
: LIVE
  PRODUCT DESCRIPTION
SPECIFICATION
ITEM
DESCRIPTION
Power Requirements
230 - 240 Volts
50 Hertz
Single phase, 3 wire earthed
Power Consumption
1.24 kW
Power Output
800 W nominal of RF microwave energy (measured by method of IEC 705)
Operating frequency 2450 MHz
Case Dimensions
Width
449 mm
Height
282 mm including foot
Depth
385 mm
Cooking Cavity Dimensions
Width
287 mm
Height
220 mm
Depth
311 mm
Turntable diameter
272 mm
Control Complement
Touch Control System
Clock (1.00 - 12.59 or 0.00 - 23.59) - 12HR or 24HR setting
Timer (0 - 99 minutes and 90 seconds)
Microwave Power for Variable Cooking
Repetition Rate;
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
Time pads, Instant Cook pads
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
Set Weight
Approx. 13.3 kg
R-252M   4
CONTROL PANEL
1. Place the roller stay on the floor of the oven cavity, engaging
shaft into turntable motor shaft.
2. Then place the turntable on roller stay.
4. Oven lamp
5. Control panel
6. Rubber seal
7. Door latch openings
8. Oven cavity
9. Door seals and sealing surfaces
10.Safety door latches
11.Ventilation openings
12.Outer case
13.Power supply cord
  APPEARANCE VIEW
OVEN
1. Door
2. Door hinges
3. Waveguide cover
3
4
1
10
7
6
2
9
8
11
5
12
13
STIR
KG PCS
TURN
COOK
MICRO
10min.
10sec.
1min.
FRESH FISH
MINCED MEAT
FRESH VEG.
CANNED FOOD
SPONGE PUDDING
CAKE
1 Roast Beef/
Lamb
2 Roast Pork
3 Roast Poultry
1 Meat Joint
Beef/Lamb/Pork
2 Poultry
3 Minced Meat
JACKET POTATOES
BOILED POTATOES
RICE/PASTA
Instant Cook
AUTO
COOK
Kg Lb
POWER
LEVEL
TIMER
Kg/Lb
STOP/
CLEAR
START
AUTO MINUTE
AUTO START
CLOCK
LESS
MORE
g  oz
AUTO
DEFROST
R-252
2
3
5
10
7
12
13
4
6
8
9
11
1. DIGITAL DISPLAY
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
1
Turntable 
Roller stay
Seal packing
R-252M   5
OFF CONDITION
Closing the door activates all door interlock switches
(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 noise filter and the control panel are
energized.
Figure O-1 on page 24
MICROWAVE COOKING CONDITION
100P (HIGH) COOKING
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.
Function sequence
Figure O-2 on page 24
CONNECTED COMPONENTS
RELAY
Oven lamp, Fan motor, Turntable motor
RY1
High voltage transformer
RY3
1. The line voltage is supplied to the primary winding of
the 
high voltage
 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 signal tone is heard and
the relays RY1+RY3 open. The circuits to the oven
lamp, 
high voltage
 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.
          CONDITION
DURING
DOOR OPEN
SWITCH
CONTACT
COOKING
(NO COOKING)
Monitored switch
COM-NO
Closed
  Open
COM-NO
Closed
  Open
Monitor switch
COM-NC
Open
  Closed
Stop switch
COM-NO
Closed
  Open
The circuits to the 
high voltage
 transformer, fan motor
turntable motor, and the oven lamp are cut off when the
monitored latch switch and stop switch are made open.
6. MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by oven
door, and monitors the operation of the monitored latch
switch.
6-1 When the oven door is opened during or after the
cycle of a cooking program, 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.
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 (COM-NO) of the monitored
latch switch (SW1) and stop switch (SW3) are closed.
6-3. When the oven door is opened and the contacts
(COM-NO) of the monitored latch switches (SW1)
remain closed, the fuse will blow, because the con-
tacts (COM-NC) of the monitor switch are closed and
a short circuit is caused.
100P, 70P, 50P, 30P and 10P COOKING
When the microwave oven is preset for variable cooking
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.
SETTING;
NOTE: The ON/OFF time ratio does not exactly corre-
spond to the percentage of microwave power,
because approx. 3 seconds are needed for heat-
ing up the magnetron filament.
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%
100%
Approx. 50%
Approx. 30%
Approx. 10%
  OPERATION SEQUENCE
R-252M   6
DOOR OPEN MECHANISM
The door can be opened by pulling the door.
Figure D-1. Door Open Mechanism
MONITORED LATCH SWITCH AND STOP SWITCH
1. When the oven door is closed, the contacts (COM-NO)
must be closed.
MONITOR SWITCH
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 he contacts (COM-NO)
of the monitored latch switch fail to open, the fuse F1
blows immediately after closing the contacts (COM-
NC) of the monitor switch.
CAUTION: BEFORE REPLACING A BLOWN FUSE  F1
TEST MONITORED LATCH SWITCH (SW1)
AND  MONITOR SWITCH FOR PROPER
OPERATION.  (REFER TO CHAPTER “TEST
PROCEDURE”).
FUSE
1. The fuse F1 blows when the contacts (COM-NO) of the
monitored latch switch remain closed with the oven
door open and when the contacts (COM-NC) of the
monitor switch are closes.
2. If the wire harness or electrical components are short-
circuited, the fuse F1 blows to prevent an electric shock
or fire hazard.
HVT THERMOSTAT 150˚C
The thermostat protects the high voltage transformer
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.)
Latch hook
SW3: Stop switch
Door
SW2: Monitor switch
SW1:Monitored latch switch
Latch heads
THERMAL CUT-OUT 125˚C (OVEN)
The thermal cut-out located on the top of the oven cavity
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
one.
TURNTABLE MOTOR
The turntable motor drives the turntable roller assembly to
rotate the turntable.
FAN MOTOR
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. 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.
NOISE FILTER
The noise filter assembly prevents radio frequency inter-
ference that might flow back into the power circuit.
   FUNCTION OF IMPORTANT COMPONENTS
R-252M   7
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. Check the monitored latch
switch and monitor switch before replac-
ing the F1 fuse.
   TROUBLESHOOTING GUIDE
CONDITION
PROBLEM
A
B
C
D
E
E E
F G
H
I
I
J
K
L
L
M
Home fuse blows when power cord 
is plugged into wall outlet.
Fuse F1   blows when power cord 
is plugged into wall outlet. (Timer 
off)
All letters and indicators do not 
appear in display when power cord 
is first plugged into wall outlet.
Display does not operate properly 
when Stop/Clear pad is touched. 
(Buzzer should sound and "  ;  " or 
time of day should appear in display.
Oven lamp does not light, when in 
operation. 
Fan motor does not operate. 
Turntable motor does not operate. 
Oven or electrical parts does not 
stop when cooking time is 0 or 
Stop/Clear pad is touched. 
Oven seems to be operating but 
little or no heat is produced in oven 
load. (Microwave power level is set 
at HIGH.)
Oven does not operate properly during 
the variable cooking condition except 
100% (HIGH) cooking condition.
Oven goes into cook cycle but 
shuts down before end of cooking 
cycle.
Oven stops as soon as the oven is 
started.
Fan motor, oven lamp and 
turntable motor do not operate at 
the same time.
OFF
CONDITION
COOKING
CONDITION
TEST PROCEDURE
POSSIBLE CAUSE
AND
DEFECTIVE PARTS
MAGNETRON
HIGH VOLTAGE  TRANSFORMER
H.V. RECTIFIER
HIGH VOLTAGE CAPACITOR
MONITORED LATCH SWITCH
STOP SWITCH
MONITOR SWITCH
THERMAL CUT-OUT 125
ß
C
FUSE F1
NOISE FILTER
FAN MOTOR
TURNTABLE MOTOR
POWER SUPPLY CORD
OVEN LAMP OR SOCKET
SHORTED WIRE HARNESS
OPENED WIRE HARNESS
MIS-ADJUSTMENT SWITCHES
NO POWER AT WALL OUTLET
HVT THERMOSTAT
CONTROL UNIT
KEY UNIT
RELAY RY1
RELAY RY3
FOIL PATTERN ON P.W.B.
R-252M   8
 
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
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).
The IEC-705 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-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.
Note:  The result from this test should be within the allowance of 2000cc alternative
method. (+-10%).
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
(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-252M   9
 TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
B
HIGH VOLTAGE  TRANSFORMER TEST
WARNING:
High voltage and large currents are present at the secondary winding and
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.
CARRY OUT 3D CHECKS.
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
obtained:-
a. Primary winding .......................... 2.2 ohms approximately
b. Secondary winding .................... 140 ohms approximately
c. Filament winding .....................................  less than 1 ohm
If the readings obtained are not stated as above, then the high voltage transformer is probably faulty
and should be replaced.
CARRY OUT 4R CHECKS.
C
HIGH VOLTAGE RECTIFIER TEST
CARRY OUT 3D 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
 in the other direction.
CARRY OUT 4R CHECKS.
NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF
THE MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BECAUSE
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.
D
HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
A. Isolate the high voltage capacitor from the circuit.
B. Continuity check must be carried out with measuring instrument which is set to the highest
resistance range.
C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10M
 after
it has been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 M
 because of its internal 10M
resistance.
F. When the internal wire is opened in the high voltage capacitor, the capacitor shows an infinite
resistance.
G. The resistance across all the terminals and the chassis must be infinite when the capacitor is  normal.
If incorrect reading are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS.
R-252M   10
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the thermal cut-out. Then using an ohmmeter, make a
continuity test across the two terminals as described in the below.
CARRY OUT 4R CHECKS.
Temperature of "ON" condition  (closed circuit). ................................................... This is not resetable type
Temperature of "OFF" condition (open circuit). ....................................................................... Above 125˚C
Indication of ohmmeter (When room temperature is approx. 20˚C.) ....................................... Closed circuit
If incorrect readings are obtained, replace the thermal cut-out.
An open circuit thermal cut-out (OVEN) indicates that the food in the oven cavity may catch fire, this
may be due to over heating produced by improper setting of the cooking timer or failure of the control
panel.
  TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
E
SWITCH TEST
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals
as described in the following table.
COM; Common terminal,
NO;
Normally open terminal
NC;
Normally close terminal
If incorrect readings are obtained, replace the switch.
CARRY OUT 4R CHECKS.
F
THERMAL CUT-OUT TEST
Table: Terminal Connection of Switch
Plunger Operation
COM to NO
COM to NC
Released
Open circuit
Short circuit
Depressed
Short circuit
Open circuit
G
BLOWN FUSE
CARRY OUT 3D CHECKS.
1. If the fuse is blown, there could be a shorts or grounds in electrical parts or wire harness. Check them
and replace the defective parts or repair the wire harness.
2. If the fuse is blown when the door is opened, check the monitored latch switch and monitor switch.
If the fuse is blown by incorrect door switching replace the defective switch(es) and the  fuse F1.
CARRY OUT 4R CHECKS.
CAUTION:
Only replace fuse with the correct value replacement.

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