R -4A52
R-4E52
SHARP SERVICE MANUAL
S0005R4A52PJZ
I’
MICROWAVE OVEN
MODELS
R-4A52
Photo R-4A52
R -4,E52
In interests of user-safety the oven should be restored to its original
condition and only manufacturer original spare parts must be used.
TABLE OF CONTENTS
GENERAL IMPORTANT INFORMATION
Page
......................................................................................................
1
CAUTION, MICROWAVE RADlATION,WARNING ......................................................................................
PRODUCT SPECIFICATIONS
1
.........................................................................................................................
APPEARANCE VIEW 2 ........................................................................................................................................
OPERATION SEQUENCE 3 .................................................................................................................................
FUNCTION OF IMPORTANT COMPONENTS
4
SERVICING
..............................................................................................
5
............
TEST PROCEDURE
............................................................................................................................................
7
........................................................................................................................................
TOUCH CONTROL ASSEMBLY
10
COMPONENT REPLACEMENT AN’~..~~J.USTM’ENT.PR.O.~E.~UR E ..IIII:::::::I::::::::::::::::::::I:::IIIII::::::Il::::
17
MICROWAVE MEASUREMENT
23
TEST DATA AT A GLANCE
...................................................................................................................
30
WIRING DIAGRAM
................................................................................. -.
........................................
31
.......................
PICTORIAL DIAGRAM
.
...............................................................................................................
32
...
....
CONTROL PANEL CIRCUIT
...........................................................................................................................
34
. .
PRINTED WIRING DIAGRAM
.......................................................................................................................
36
PARTS LIST
.....................................................................................................................
38
....................................................................................................................................................
PACKING AND ACCESSORIES
39
...................................................................................................................
45
SHARP CORPORATION
R-4A52
R-4E52
SERVICE MANUAL
SHARP
MICROWAVE OVEN
R-4A521 R-4E52
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 microwave 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
“*Il on parts list are used at voltages
more than 25OV.
SHARP CORPORATION
OSAKA, JAPAN
1
= .” PRODUCT SPECIFICATIONS
.r*&, “7:
OPERATING SEQUENCE
TROUBLESHOOTING CHAR
TEST PROCEDURE
TEST DATA TABLE AND
TEST POINTS ON CONTROL
i$~~?;# ,,,,,Rl,,,G ,-JlAGRA,,,,
-i” -A
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PRINTED WIRING BOARD
,,&;:$:
nit
,d PARTS LIST
“yb
R -4A52
R-4E52
PRODUCT SPECIFICATIONS
SPECIFICATION
ITEM
Power Requirements
_-
Power Consumption
Power Output
____
Outside Dimensions
Cooking Cavity Dimensions
Turntable diameter
Control Complement
Set Weight
DESCRIPTION
240 Volts
50 Hertz
Single phase, 3 wire earthed
14oow
’ 750 watts nominal of RF microwave energy (2 liter water load)
Operating frequency of 2450M Hz
-
’ Width 550mm
Height 312mm
‘-Depth 417mm for R-4E52
420mm for R-4A52
Width 381 mm
1 Height 210 mm
Depth 411 mm
360mm
Touch Control System
Clock( 1 :OO - 12:59 )
Timer (0 - 99 minutes 99 seconds )
Microwave Power for Variable Cooking
Repetition Rate;
HIGH *.........*....................*.
Full power throughout the cooking time
MEDIUM
HIGH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
approx.
70% of Full
Power
MEDIUM
..,...,,..................*.........*..........,.* approx. 50% of Full Power
MEDIUM LOW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
approx.
30% of Full Power
LOW
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
approx. 10% of Full Power
For R-4A52
For R-4E52
AUTO COOK
INSTANT ACTION
EASY REHEAT
EASY DEFROST
EASY DEFROST
DOUBLE QUANTITY
INSTANT COOK/START
TRIPLE QUANTITY
MEMORY
AUTO START/CLOCK
AUTO START/CLOCK
POWER LEVEL
VARIABLE COOKING CONTROL
NUMBER
NUMBER
INSTANT COOK/START
STOP/CLEAR
STOP/CLEAR
Approx. 17.0 kg
2
:.
APPEARANCE VIEW
R-4A52
R-4E52
1.
Ventilation
openings
8. Touch Control Panel
2. Oven lamp
9. Digital readout
3. Hinges
10. Waveguide cover
4. Safety door latches 11. Access cover for oven lamp replacement
5. See through door
12. Power supply cord
6. Coupling
13. Roller Stay
7. Door open
button
14. Turntable
i
Touch Control Panel for R-4A52
AUTO COOK MENUS
1
NUMBER PADS
clock trme. wecght or quantrty
of food, or to select the Auto
Cook or Easy Reheat menus.
VARIABLE COOKING
CONTROL PADS
Touch to select microwave
power settmg.
ff not touched, HIGH is automatrcally selected.
STOP/CLEAR PAD
Touch to erase during programming.
Touch once to stop operatron
of oven during cookmg; touch
lwce to cancel cookrng pro---gramme.
- EASY REHEAT PAD
Touch to select EasV Reheat
mode.
-EASY REHEAT MENUS
-EASY DEFROST PAD
Touch to defrost meat by
entering weight.
. MEMORY
Touch to enter one frequently
used cookmg programme.
Touch to recall the memonzed
programme.
‘MOREI n I. LESS( v 1 PADS
Touch to increase/decrease
the time in one mcnute mcrements during cookmg or to
increase/decrease the trme
whrlst programmrng the Easy
Reheat, Auto Cook or Easy
Defrost modes.
INSTANT COOK/START PAD
Touch once to cook for 1
mmute at HIGH or Increase by
1 mrnute multrples each trme
this pad IS touched during
cookmg.
Touch to start oven after
settmg programmes.
*Place the roller stay on
the coupling in the oven
and seat the turntable on
the roller stay.
Touch Control Panel for R-4E52
7 INSTANT ACTION -
INSTANT ACTION PADS
Touch once to cook or reheat 10 popular menus
entenng weight.
touchmg the INSTANT ACTION
pad.
wL2zl(I 111
-TRIPLE QUANTITY PAD
To cook triple quantrty, touch this pad prior to
touchrng the INSTANT ACTION pad.
I INUMBER PADS
Touch to enter weight, cookrng and clock trmes
Touch to select cooking power control settmg.
AUTO START/CLOCK PAD
Touch to set clock or Auto Start trme.
‘INSTANT COOK/START PAD
Touch once to cook for 1 minute at HIGH or
increase by 1 minute multiples each trme thus pad IS
touched dunng cookmg. Touch to start oven after
setting programmes.
J
L STOP/CLEAR PAD
Touch to erase during programming.
Touch once to stop operatron of oven dunng
cookrng; touch twrce to cancel cooking programme.
R-&u2
R-4E52
OPERATING SEQUENCE
OFF CONDITION
Closing the door activates all door interlock switches
(Upper latch switch,
Lower 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 pluged in a wall outlet
(240V 50Hz), 240 volts A.C. is supplied to the point
Al + A3 in the control unit.
Figure O-l on page 32 or 33
1 . The display flashes “88:88”. --
2. To set any programmes or set the clock, you must
first touch the STOP/CLEAR key.
3. [lappears in the display and the time counts
up every minute.
NOTE: When the oven door is opened, the oven
lamp comes on at this time.
MICROWAVE COOKING CONDITION
HIGH COOKING
Enter a desired cooking time with the touching
NUMBER key and start the oven with touching
START key.
Function sequence Figure O-2 on page 32 or 33
CONNECTED COMPONENTS
RELAY
Oven lame, Fan motor, Turntable motor
RYI
Power transformer
RY2
1. 240 volts AC. is supplied to the primary winding
of the power transformer. The voltage is converted
to about 3.3 volts AC. 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 voltagedoubling 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 channeled 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 RYI + RY2 go back to their home
position.
The circuits to the oven lamp, power
transformer, fan motor and turntable motor are cut
off.
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)
Upper latch switch COM - NO Closed
Open
Monitor switch
COM- NC
Open ’ Closed
Lower latch switch COM - NO Closed
Open
Stop switch
COM- NO Closed
Open
The circuits to the power transformer, fan motor and
turntable motor are cut off when the upper latch
switch, and stop switch are made open.
The oven lamp remains on even if the oven door is
opened after the cooking cycle has been interrupted, because the relay RYI stays closed. Shown
in the display is the remaining time.
MONITOR SWITCH CIRCUIT
The monitor switch SW3 is mechanically controlled
by oven door, and monitors the operation of the
upper and lower latch switches SW1 + SW2.
6-2
When the oven door is opened during or after the
cycle of a cooking program, the upper latch and
lower latch switches SW1 + SW2 must open their
contacts first.
After that the contacts (COM NC) of the monitor switch SW3 can be closed
and then contacts of the stop switch SW4 can be
opened.
When the oven door is closed, the contacts
(COM-
NC) of the monitor switch SW3 must
be opened first, and the contacts (COM - NO)
of the stop switch SW4 must be closed. After that
the contacts of the upper latch switch SW1 latch
and lower latch switches SW1 + SW2 are closed.
6-3. When the oven door is opened and the contacts
of the upper and lower latch switches SW1 +
SW2 remain closed. The fuse E M8A will blow,
because the monitor switch is closed and a short
circuit is caused.
4
R-4A52
R-4E52
MEDIUM HIGH, MEDIUM, MEDIUM LOW,
SETTING
LOW COOKING
When the microwave oven is preset for variable cooking power, 240 volts A.C. power 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 RY2.
The following
levels of microwave power are given.
HIGH
MEDIUM HIGH
MEDIUM
MEDIUM LOW
LOW
32 sec. ON
24 sec. ON 8 sec. OFF
-1 Approx. 70% = 525 Watts
lEsac.ON 14 sec. OFF
m-1 Approx. 50% = 375 Watts
12secON 20 sec. OFF
m-1 Approx. 30% = 225 Watts
6 sec. ON 26 sac. OFF
m------j Approx. 10% = 75 Watts
NOTE: The ON/OFF time ratio does not exactly corre-
I
spond to the percentage of microwave power,
because approx. 2 seconds are needed for
heating up the magnetron filament.
FUNCTION OF IMPORTANT COMPONENTS
DOOR OPEN MECHANISM
The door can be opened by pushing the door open
button on the control panel. When the door open
button is pushed, the latch lever is moved upward,
operating the latch head. The latch head is moved
upward, and released from the latch hook. Now, the
door can be opened.
.LATCH MONITOR
HOOK \
, SWITCH
DOOR
LATCH
HEAD
KE
SWITCH
I
-. -.
SWITCH
LOWER
kGGON~ L -s-w:T:! _ _ /
--7
Figure D-l. Door Open Mechanism
UPPER LATCH SWITCH SW1
LOWER LATCH SWITCH SW2
STOP SWITCH SW4
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.
M’ONITOR SWITCH SW3
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 the contacts
(COM -
NO) of the upper and lower latch switches
SW1 + SW2 fail to open, the fuse E M8A blows simultaneously with closing the contacts (COM- NC)
of the monitor switch SW3
CAUTION: BEFORE REPLACING A BLOWN FUSE F
M8A TEST THE UPPER AND LOWER
LATCH SWITCHES SW1 + SW2 MONITOR SWITCH SW3 AND MONITOR RESISTOR FOR
OPERATlON.(:EFER TO
PROPER
CHAPTER
“TEST PROCEDURE”.)
MONITOR RESISTOR- R 0.8 Q 20W
The monitor resistor prevents the fuse E M8A bursting
when the fuse E M8A blows due to the operation of
the monitor switch.
THERMAL CUT-OUT TC 145°C (OVEN)
The thermal cut-out located on the top of the oven
cavity is designed to prevent damage to the oven if the
foods in the oven catch fire due to over heating
produced by unproper setting of cook time or failure
of control unit.
Under normal operation, the oven thermal cut-out re-
mains closed. However, when abnormally high temperatures are reached within the oven cavity, the oven
thermal cut-out will open at 145”C, causing the oven
to shut down.
The thermal cut-out TC will be close its contacts again
when its temperature goes down lower than -20°C.
5
R-4A52
R-4E52
FUSE _E M8A 250A
1. If the wire harness or electrical components are
short-circuited, this fuse blows to prevent an elec-
tric shock or fire hazard.
2. The fuse blows when the asymmetric rectifier, H.V.
rectifier,
H.V. wire harness, H.V. capacitor,
magnetron or secondary winding of power transformer is shorted.
3. The fuse also blows when upper and lower latch
switches SW1 + SW2 remains closed with the oven
door open and when the monitor switch SW3
closes.
TEMPERATURE FUSE E 150”C(MG)
This fuse protects the magnetron against overheating.
If the temperature goes up higher than 150°C because
the fan motor is interrupted, the air inlet duct is blocked
or the ventilation openings are obstructed, the fuse
blows and puts the oven out of operation. The defective fuse must be replaced with new rated 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 channeled through the oven cavity to remove
steam and vapors given off from the heating foods. It
is then exhausted through the exhausting air vents at
the oven cavity
ASYMMETRIC RECTIFIER
The asymmetric rectifier is a solid state device that
prevents current flow in both directions. And it prevents the temperature rise of the power transformer by
blowing the fuse E M8A when the high voltage rectifier
is shorted.
*qlG” VOLTAGE RECTIF,ER
The rated peak reverse voltage of Dl of the asymmetric
rectifier is 6 KV The rated peak reverse voltage of D2
of the asymmetric rectifier is 1.7 KV. Dl 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 blowing the fuse E M8A.)
1.
2.
3.
4.
5.
6.
7.
The high voltage rectifier is shorted by any causes
when microwave cooking.
The peak reverse voltage of D2 of the rectifier goes
beyond the rated peak reverse voltage 1.7 KV in the
voltage doubler circuit.
D2 of the rectifier is shorted.
The large electric currents flow through the high
voltage winding of the power transformer.
The large electric currents beyond 8A flow through
the primary winding of the power transformer.
The fuse E M8A blows by the large electric currents.
The power supply to the power transformer is cut
off.
NOISE FILTER
(For New Zealand Model)
The noise filter prevents the radio frequency interference that might flow back in the power circuit.
R-4A52
R-4E52
SERVICING
WARNING TO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of producing very high voltage and current, contact with any part
of the high voltage circuit will result in electrocution.
REMEMBER TO CHECK 3D
REMEMBER TO CHECK 4R
1) Disconnect the supply.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.
WARNING AGAlNST THE CHARGE OF THE
HIGH-VOLTAGE CAPACITOR
1) Reconnect all leads removed from components
during testing.
2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run the oven. Check all functions.
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 connection 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.
Microwave ovens shouid 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 power level to
HIGH. And set the timer for two (2) minutes. 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
Sharp
recommend
that
wherever possible
the connections to the component being tested.
faultifinding is carried out with the supply.disconnetted. It may in,
some cases, be necessary to
connect the supply after the outer case has been
removed, in this event carry out 30 checks and then
disconnect the leads to the pnmary of the power
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 ofihe power transformer.
When all service work is completed, and the oven is fully assembled, the microwave power output should
be checked and a microwave leakage test carried out.
TROUBLESHOOTING GUIDE
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 procedure letter which wiil be found in the
“Test Procedure”section.
IMPORTANT: If the oven becomes inoperative be-
cause of a blown fuse E (M8A) in the
upper latch switch - lower latch
switch - monitor switch - monitor
resisitor circuit, check the lower latch
switch, monitor switch and monitor
resistor before replacing the fuse E
(M8A).
7
R-4A52
R-4E52
NOTE: “0” means direct cause and part. “A” means indirect cause and part.
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PROBLEM
2
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Home fuse blows when power supply
cord is plugged into wall outlet.
Fuse M8A blows when power supply
cord is plugged into wall receptacle.
0 0
88 : 88 does not appear in display but
OFF
CONDITION
power supply cord is plugged into wall
0
outlet.
Display does not operate properly when
STOP/CLEAR pad is touched.
Oven lamp does not light at door
opened. (Display appears.)
Oven does not start when START pad
is touched. (Display appears.)
0
0
Oven lamp does not light. (Display
appears.)
Fan motor does not operate. (Display
appears.)
0
Turntable motor assembly does not
operate. (Display apears.)
0
Oven or any electrical parts does not
stop. But cooking time is 0 or
STOP/CLEAR pad is touched.
IN
:ONDITION
Oven seems to be operating but little or
no heat is produced in oven load. (Micro-
000 00 0
wave power level is set at HIGH.)
Oven does not seem to be operating
properly when MEDIUM HIGH, MEDIUM, MEDIUM LOW or LOW is set. (Oven
operates properly at HIGH and then the
STOP/CLEAR pad is touched the oven
stops.)
Oven goes into cook cycle but shuts
down before end of cooking cycle.
Oven stops as soon as when the START
pad is touched.
ALlAAnn
8
R -4A52
R-4E52
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R -4A52
R-4E52
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
MAGNETRON TEST
-----. -
-
j NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED
I
1 TOOL WHILE THE OVEN IS IN OPERATION.
CARRY OUT 3D CHECKS
Isolate the magnetron from the high voltage circuit by removing all leads connected to the 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 a short circuit 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 inifinite
resistance. If a low or zero resistance reading is obtained then the magnetron should be replaced.
MICROWAVE OUTPUT POWER
The following test procedure should be carried out with the microwave oven in a fully assembled
condition (with outer case fitted).
Microwave output power from the magnetron can be measured by way of substitution, i.e. it can
be measured by using a water load how much it can be absorbed by the water load. 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/4.2 calorie is generated. On the
other hand, if the temperature of the water with V(ml) rises AT (“C) during this microwave
heating period, the calorie of the water is V x AT.
1 The formulae is as follows;
I
P x t / 4.2 = V x AT
P (W) = 4.2 x V x AT / t
Our condition for the water load is as follows:
Room temperature . . .
around 2O”C, Power supply Voltage . . . 240 volts.
Water load . . .
2000 ml, Initial temperature . . . 1 O&l OC, Heating time . ..I min. 52 sec.
P = 75 x AT
Measuring method:
A) Use two 1 litre Pyrex beakers with a diameter of approximately of 12cms.
B) Place 1 litre of 10°C water in each beaker.
C) Mark Tl on the one beaker and mark T2 on the other one. And stir the water and measure the
temperature of water the thermometer and note them. The graduation of the thermometer must
be scaled by 0.1 “C at minimum and an accurate mercury thermometer is recommended.
Example: The initial temperature Tl = 1 O’C, T2 = 11 “C
D) Place the two beakers as touching each other in the centre of the cavity.
E) Set the timer to 1 minute 52 seconds at 100% power (the time required to raise the water
temperature 10 degrees C.)
F) The time must be measured with stopwatch or wristwatch.
G) After 1 minute and 52 seconds, stop the oven by opening the door.
H) Remove the two beakers from the oven and measure the temperature of the water by stiring the
water with the thermometer and noting the readings.
10
R-4A52
R-4E52
TEST PROCEDURES (CONT’D)
PROCEDURE
LETTER
COMPONENT TEST
Example: Tl = 20°C, T2 = 21 “C
initial temperature
~~
Temperature after 1 min. 52 sec.
Temperature difference Cold-Warm
---
Mean temperature rise LIT
i
T
T
Measured output power
The equation is as follows:
P= 75 x AT
Tl
‘=lO”C T2=11”C
I
Tl = 20°C T2 = 21 “C
,!LTl =lO”C LIT~=IO”C /
-------------,
LIT = (LIT1 + LLT2) / 2
!
= (10°C + IOOC) / 2
j
= 10°C
P= 75 x 10°C
= 750 Watts
-I
NOTE:
The measured output power should be at least +I5 % of the rated
output power.
CAUTION: 1 “C CORRESPONDS TO 75 WATTS.
REPEAT MEASUREMENT IF THE POWER IS INSUFFICIENT.
(Tl OC)
lT2 OC)
(T2 OCI
Heat up for 1 min. 52 sec.
B
POWER TRANSFORMER TEST
WARNING: High voltages and large currents are present at the secondary winding
and filament winding of the power 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 D CHECKS.
Disconnect the leads to the primary winding of the power’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 windings. The following readings
should be obtained :-
a. Primary winding ------b.
---l .42 ohms approximately.
Secondary winding - - - - - - -78.9 ohms approximately.
c. Filament winding ---------less than 1 ohm.
If the reading obtained are not as stated above, then the power transformer is probably faulty and
should be replaced.
CARRY OUT 4R CHECKS
11
R-4A52
R-4E52
TEST PROCEDURES (CONT’D)
PROCEDURE
LETTER
COMPONENT TEST
C
HIGH VOLTAGE RECTIFIER ASSEMBLY TEST
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
B+C of the high voltage rectifier and note the reading obtained. Reverse the meter leads and note
this second reading. The normal resistance is intinte in one direction and mor than 100 kQ in
the other direction.
CARRY OUT 4R CHECKS
ASYMMETRIC RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier can be
tested using an ohmmeter set to its highest range. Connect the ohmmeter across the terminals
A+B of the asymmetric rectifier and note the reading obtained. Reverse the meter leads and note
this second reading. If an open circuit is indicated in both directions then the asymmetric rectifier
is good. If an asymmetric rectifier is shorted in either direction, then the the asymmetric rectifier
is probably faultly and must be replaced with the high voltage rectifier. When the asymmetric
rectifier is defective, check whether magnetron, high voltage rectifier, high voltage wire or filament winding of the power transformer is shorted.
CARRY OUT 4R CHECKS
* +z$“:H “OLTAOE
RECT,F,ER
C
NOTE:
FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES
OF THE MEASURING INSTRUMENT MUST HAVE A VOLYAGE AT LEAST 6 VOLTS,
BECAUSE O*THERWISE 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
10 Mf2 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 MO because of its internal 10
MO 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 inifinte when the capacitor
is normal.
If incorrect readings are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS
12
R -4A52
R-4E52
TEST PROCEDURES (CONT’D)
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.
Table: Terminal Connection of Switch
Plunger Operation
Released
Depressed
COM to NO
COM to NC
O.C. S.C.
_--- ---
S.C. O.C.
COM; Common terminal
S.C.; Short circuit
NO; Normally open terminal O.C.; Open circuit
NC; Normally closed terminal
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
F NOISE FILTER TEST
CARRY OUT 3D CHECKS
Disconnect the leads from the terminal’
of the noise filter.
WHT
N*
0
g--Q
Using an ohmmeter, check between the
terminals as described in the following
table.
L hinl
Cx*ZO% CvtZmb
1.0 mti
0.066,lF 22OOpF
MEASURING POINTS
Between N and L
/ INDICATION OF OHMMETEf2i
1
I Open circuit
I
I
1 Between terminal N and WHITE
Short circuit
I
I
-..-----4
Between terminal L and RED Short circuit
---
----l
If incorrect readings are obtained, replace the noise filter unit. CARRY OUT 4R CHECKS
MONITOR RESISTOR TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the monitor resistor.
-<
Using an ohmmeter and set on a low range. .
Check between the terminals of the monitor resistor as described in the following table.
Table: Resistance
Resistor
Resistance
Monitor resistor Approx. 0.8R
If incorrect readings are obtained, replace the monitor resistor,
CARRY OUT 4R CHECKS.
13
R -4A52
R-4E52
TEST PROCEDURES (CONT’D)
PROCEDURE
LETTER COMPONENT TEST
H
TEMPERATURE FUSE OR THERMAL CUT OUT TEST
CARRY OUT 3D CHECKS
Disconnect the leads from the terminals of the temp. fuse or thermal cut-out. Then using an
ohmmeter, make a continuity test across the each two terminals as described in the table below.
CARRY OUT 4R CHECKS
Table: Temperature Fuse Test
Parts F-ame
Temperature of Temperature of Indication of
“ON” condition . “OFF” condition ohmmeter
(closed circuit).
(open circuit). (When room
(“Cl
(“Cl
temperature is
approx. 20°C.)
Temp. fuse 1 50°C
(Magnetron)
Thermal cut-out
145°C (Oven)
This is not resetable
Above 1 50°C Closed circuit
type.
- 20°C
Above 145’C Closed circuit
If incorrect readings are obtained, replace the temp. fuse or thermal cut-out.
An open circuit temperature fuse (MG) indicates that the magnetron has overheated, this may
be due to resistricted ventilation, cooling fan failure or a fault condition within the magnetron
or HV circuit.
An open circuit thermal cut-out (OVEN) indicates that the foods in the oven catch fire, this may
be due to over heating produced by unproper setting of the cooking timer or failure of the control
panel.
MOTOR WINDING TEST
CARRY OUT 30 CHECKS
Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two
terminals as described in the table below.
Table: Resistance of Motor
1 Motors
I
Resistance
i F an motor
1 Approximately 246f2
1 Turntable motor
1 Approximately 12.5kn
If incorrect readings are obtained, replace the motor. (Also refer to test procedure J)
CARRY OUT 4R CHECKS
14
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