R-420BK
R-420BW
SHARF?
SERVICE MANUAL
S28M104R420BE
MICROWAVE OVEN MODELS
R-420BK / R-420BW
In the interest of user-safety the oven is to be restored
to its original condition and only the parts identical to
those specified should be used.
WARNING TO SERVICE PERSONNEL: Microwave
ovens contain circuitry capable of producing
very high voltage and current. Contact with the
following parts may result in a severe, possibly
fatal electrical shock.(High Voltage Capacitor,
High Voltage Power Transformer, Magnetron,
High Voltage Rectifier Assembly, High Voltage
Harness etc..)
TABLE OF CONTENTS
SECTION
PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICE TO
AVOID POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY.
Before Servicing .............................................................
Warning to Service Personnel
Forewordandwarning .......................................................................
Specifications
Generallnformation .........................................................................
KeyUnitLayout .............................................................................
Operation ..................................................................................
Servicing and Troubleshooting Guide
TestProcedures
TouchControlOutline .......................................................................
Component Replacement and Adjustment Procedure
Microwave Measurement Procedure
Wiring/Schematic Diagram
Parts .....................................................................................
Packing and Accessories ....................................................................
...............................................................................
............................................................................
.................................................................
..........................................................
...........................................
..........................................................
..................................................................
SHARP ELECTRONICS CORPORATION
...........
PAGE
Inside Front Cover
Inside Front Cover
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46
Service Headquarters: Sharp Plaza, Mahwah, New Jersey, 07430-2135
R-420BK
R-420BW
a
Do not operate or allow the oven to be operated with the door open.
( )
Make the following safety checks on all ovens to be serviced before activating the magnetron
(b)
or other microwave source, and make repairs as necessary: (1) Interlock operation, (2) proper
door closing, (3) seal and sealing surfaces (arcing, wear, and other damage), (4) damage to
or loosening of hinges and latches, (5) evidence of dropping or abuse.
C
Before turning on microwave power for any service test or inspection within the microwave gen-
( )
erating compartments, check the magnetron, waveguide or transmission line, and cavity for
proper alignment, integrity, and connections.
Any defective or misadjusted components in the interlock, monitor, door seal, and microwave
No
generation and transmission systems shall be repaired, replaced, or adjusted by procedures
described in this manual before the oven is released to the owner.
e
A microwave leakage check to verify compliance with the Federal Performance Standard
( )
should be performed on each oven prior to releasing oven to the owner.
Before servicing an operative unit, perform a microwave emission check as per the Microwave
Measurement Procedure outlined in this service manual. If microwave emissions level is in excess
of the specified limit, contact SHARP ELECTRONICS CORPORATION immediately @
l-800-237-4277.
If the unit operates with the door open, service person should 1) tell the user not to operate the oven
and 2) contact SHARP ELECTRONICS CORPORATION and DHHS immediately.
(RD21101U)
Service personnel should inform SHARP ELECTRONICS CORPORATION of any certified unit
found with emissions in excess of 4mW/cm2. The owner of the unit should be instructed not to use
the unit until the oven has been brought into compliance.
(RD81001 U)
SERVICE MANUAL
SHARI?
R-420BK
R-420BW
Microwave Ovens
R=420BK/R=420BW
Foreword
This manual has been prepared to provide Sharp
Electronics Corporation personnel with complete
operation and service information for Sharp microwave
oven models R-420BWR-420BW.
It is recommended that service personnel carefully
study the entire text of this manual so they will be
qualified to render satisfactory customer service.
Check interlock switches and the door seal carefully.
Special attention must be given to avoid electrical shock
and microwave radiation hazards.
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 are no other visible signs of damage to the
oven.
DANGER
Certain initial parts are intentionally not grounded
and present a risk of electrical shock only during
servicing. Service personnel - Do not contact the following parts while the appliance is energized;
High Voltage Capacitor, Power Transformer, Magnetron, High Voltage Rectifier Assembly and High voltage Harness.
If provided, Vent Hood, Fan Assembly and Cooling
Fan motor.
All of the parts marked
ages more than 25OV.
Removal of the outer case cabinet gives access to voltage above 250V.
All of the parts marked “A” on parts list may cause undue
microwave exposure, by themselves, or when they are
damaged, loosened or removed.
“*” on parts list are used at volt-
Specifications
General Information
Key Unit Layout
b
Operation
Troubleshooting /
Touch Control Panel
Component Replacement
and Adjustment
Microwave Measurement
Wiring / Schematic
Diagram
Sharp Electronics Corporation
Sharp Plaza
Mahwah, New Jersey 07430-2135
R-420BK
R-420BW
WARNING TO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of
producing very high voltage and current. Contact with following parts may result in a severe,
possibly fatal, electrical shock.
(EXAMPLE)
High Voltage Capacitor, High Voltage Power
Transformer, Magnetron, High Voltage Rectifier
Assembly, High Voltage Harness etc..
Read the Service Manual carefully and follow all
instructions.
Before Servicing
Rage
1. Disconnect the power supply cord and then remove
outer case
2. Open the door and block it open.
3. Discharge the high voltage capacitor.
WARNING:RlSK QF ELECTRICAL SHOCK. DISCHARGE
THE HIGH VOLTAGE CAPACITOR BEFORE SERVICING.
The high-voltage capacitor remains charged about 60 se-
conds after the oven has been switched off. Wait for 60 se-
1 conds and then short-circuit the connection of the high volt-
~ age capacitor (that is the connecting lead of the high voltage
rectifier) against the chassis with the use of an insulated
screwdriver.
Whenever troubleshooting is performed, the power supply must be disconnected. In some cases it may be necessary to connect the power supply after the outer case
has been removed, in this event:
1.
Disconnect the power supply cord, and then remove
outer case cabinet.
2.
Open the door and block it open.
3.
Discharge the high voltage capacitor.
4.
Disconnect the leads to the primary of the power
transformer.
Ensure that the leads remain isolated from other
5.
components and oven chassis by using insulation
tape.
6.
After the above procedure, reconnect the power sup-
ply cord.
When the testing is completed
1. Disconnect the power supply cord and then remove
outer case cabinet.
2. Open the door and block it open.
3. Discharge the high voltage capacitor.
4. Reconnect the leads to the primary of the power
transformer.
5. Re-install the outer case cabinet.
6. Reconnect the power supply cord after the outer
case cabinet is installed.
7. Start the oven and check all functions.
After repairing
1. Reconnect all leads removed from components during testing.
2. Re-install the outer case (cabinet).
3. Reconnect the power supply cord after the outer
case is installed.
4. Reconnect the power supply cord after the outer
case is installed.
5. Run the oven and check all functions.
Microwave ovens should not be operated 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 to HIGH and set the microwave
timer for two (2) minutes. When the two minutes has
elapsed (timer at zero), carefully check to see if the water is hot. If the water remains cold, carry out Before
Servicing procedure and re-examine the connection 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 the microwave leakage test should be car-
ried out.
SPECIFICATIONS
R-420BK
R-420BW
Item
Power Requirements
Power Output 1100 watts (IEC-705 Test Procedure)
Case Dimensions
Cooking Cavity
1.3 Cu.Ft.
Control Complement
Description
120 Volts
14 Amperes
1650 Watts
60 Hertz
Single phase, 3 wire grounded
Operating frequency of 2450 MHz
Width 2111&”
Height 123/i’ (including feet)
Depth 1731;’
Width 15”
Height 8”/23”
Depth 163/i
Tray Size 141/8)’ Diameter
Touch Control System
Clock (I:00 - 12:59)
Timer (0 - 99 min. 99 sec.)
Microwave Power for variable cooking
Repetition Rate;
P-HI (HIGH) . . . . . . . . . Full power throughout the cooking time
P-90 . . . . . . . . . . . , . . . . . approx. 90% of full power
P-80 . . . . . . . . . . . . . . . . . approx. 80% of full power
P-70 (MED HIGH) . . . .
P-60 . . . . . . . . . . . , . . . . . approx. 60% of full power
P-50 (MED) . . . . . . . . . . approx. 50% of full power
P-40 . . . . . . . . . . . , . . . . . approx. 40% of full power
P-30 (MED LOW) . . . . .
P-20 . . . . . . , . . . . , . . . . . approx. 20% of full power
P-IO . . . . . . . . . . . , . . . . . approx. 10% of full power
P-O................... No power throughout the cooking time
approx. 70% of full power
approx. 30% of full power
Oven Cavity Light
Safety Standard
FEATURES
Instant Action
Compu Defrost
Sensor Cook
Minute Plus
Kitchen Timer
Variable Power (10)
4 Stage Cooking
Yes
UL Listed
FCC Authorized
DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J
R-420BK
R-420BW
Grounding
GENERAL INFORMATION
Instructions
This
oven
must be
appliance
only,
ommended
appliance
observe all
WARNING:
result
must be connected to a
15
Ampere
or more fused
that
a
be
provided. When installing
applicable
Improper
in
a risk
of
Where a two-pronged
is
the personal
tomer to
placed
with
pronged
an
extension
responsibility
contact a
a properly
wall
receptacle
cord must be used, it
15 ampere minimum
Oven Diagram
fully grounded at all
120
electrical
separate
codes
use of the
electric
circuit serving only
and
ordinances.
grounding
shock.
wall-receptacle is
and
obligation of
qualified
electrician and
polarized
or
use
and
a grounding adaptor. If
should be a
cord.
times.
volt,
60
This
Hz, AC
supply. It is rec-
this
this appliance,
plug
can
encountered,
the
cus-
have
it
re-
grounded three-
3-wire,
Grounded
Receptacle
Box
3
Pronged
Grounded
Receptacle
Plug
Box
Grounding
Receptacle
w
f
Grounding
Pin
3
Pronged
Receptacle
it
Do not under any circumstances cut
round grounding
prong
from this plug.
Screw
Tab
for
Grounding
Screw
or
’
remove
the
1. Digital display
2. Auto-Touch control panel
3. Door open button
4. Door latches
5. Removable turntable support
6. Removable turntable
7. Oven lamp
8. Oven door with see through window
9. Waveguide cover
10. Power Cord
4
Key Unit Layout
a. Indicators.
b. Lighted digital display.
c. SENSOR COOK pad.
Touch to cook popular items using a pre-set time
constant.Instant Action pad.
d. INSTANT ACTION pad.
Pre-set time constant for some popular food items in everyday life style
e. COMPU DEFROST pad.
Touch to defrost certain foods.
f. Number selection pads.
g. AUTO START/CLOCK pad.
Touch to set clock or auto start time.
h. KITCHEN TIMER pad.
Touch to set minute function.
i. START pad.
Touch to start oven.
j. MINUTE PLUS pad.
Touch to cook for 1 minute at 100% power or to increase
cooking time.
k. STOP/CLEAR pad.
Touch to erase during programming.
Touch once to stop operation of oven during cooking.
Touch twice to cancel cooking program.
I. POWER LEVEL pad.
Touch to select microwave power setting.
R-420BK
R-420BW
SENSOR COOK
INSTANT ACTION
COMPU DEFROS
R-420BK
R-420BW
OPERATION
Description of Operating Sequence
The following is a description of component functions
during oven operation:
interlock relay and is mechanically associated with
the door so that it functions as follows:
Off Condition
Closing the door activates the door sensing switch and
secondary interlock switch. In this condition, the monitor switch contacts are opened. When the oven is
plugged in, 120 volts AC is supplied to the control unit
(see schematic diagram). The display flashes 88:88. To
set any program or set the clock, first touch the STOP/
CLEAR pad. The display clears and “ : ” appears and the
control unit counts every minute.
Cooking Condition
Program desired cooking time and Variable Cooking
Control by touching the NUMBER pads and the Power
Level pad of the Variable Cooking Control. When
START is touched, the following operations occur:
1. The relay contacts are closed and components connected to the relays (RY-1 and RY-2) are turned on.
(For details, see table below.)
Relay Components
RY-1
RY-2
2.
120 volts AC is supplied to the primary winding of the
power transformer and is converted to approximately 3.4 volts AC on the filament winding and approximately 2400 volts AC on the high voltage winding.
3.
The filament winding voltage heats the magnetron
filament and the high voltage is sent to a voltage doubler circuit.
4. The microwave energy produced by the magnetron
is channeled through the waveguide into the cavity
feed-box and into the cavity where the food is
cooked.
5. Upon completion of the cooking cycle, the power
transformer, oven lamp and cooling fan are turned off
and the generation of microwave energy is termi-
nated.
6 .
When the door is opened during a cook cycle, the
monitor switch, door sensing switch, secondary interlock switch and primary interlock relay are activated with the following results. The turntable motor,
cooling fan motor and the high voltage components
are de-energized. The oven lamp remains on and
the digital readout displays the time still remaining in
the cook cycle when the door was opened.
7. The monitor switch is electrically monitoring the operation of the secondary interlock switch and primary
Oven Lamp/Turntable Motor/Fan Motor
Power Transformer
a.
When the door opens from a closed position, the
( )
secondary interlock switch and primary interlock
relay open their contacts, then the monitor switch
contacts close.
.
When the door is closed from the open position,
(b)
the monitor switch contacts first open and the
contacts of the secondary interlock switch close.
If the secondary interlock switch and the primary inter-
lock relay contacts are closed when the door is opened,
the monitor switch contacts form a short circuit through
the monitor fuse, secondary interlock switch and prima-
ry interlock relay causing the monitor fuse to blow.
Power Level P-O to P-90 Cooking
When Variable Cooking Power is programmed, 120
volts AC is supplied to the power transformer intermittently through the contacts of relay RY-2 which is operated by the control unit within a 32 second time base. Microwave power operation is as follows:
Vari-Mode On Time Off Time
P - HI (HIGH)
(100% power)
P - 90
(approx. 90% power)
P - 80
(approx. 80% power) 26 sec. 6 sec.
P - 70 (MED, HIGH)
(approx. 70% power)
P - 60
(approx. 60% power)
P - 50 (MED)
(approx. 50% power)
P - 40
(approx. 40% power) 16 sec. 16 sec.
P - 30 (MED, LOW)
(approx. 30 % power)
P - 20
(approx. 20% power)
P-IO
(approx. 10% power) 6 sec. 26 sec.
P-O
(0% power)
The ON/OFF time ratio does not correspond with the
percentage of microwave power, because approximate-
ly 2 seconds are needed for heating the magnetron fila-
ment.
32 sec. 0 sec.
30 sec. 2 sec.
24 sec.
22 sec.
18 sec.
12 sec.
8 sec.
0 sec. 32 sec.
8 sec.
IO sec.
14 sec.
20 sec.
24 sec.
DESCRIPTION OF OPERATING SEQUENCE
R-420BK
R-420BW
The following is a description
during oven ope ration.
of
component functions
Sensor Cooking Condition
When using the SENSOR REHEAT function, the foods
are cooked without figuring time, power level or quantity.
When the oven senses enough steam from the food, it
relays the information to its microprocessor which will
calculate the remaining cooking time and the power level needed for best results.
When the food is cooked, water vapor is developed. The
sensor “senses” the vapor and its resistance increases
gradually. When the resistance reaches the value set
according to the menu, supplementary cooking is
started.
The time of supplementary cooking is determined by experiment with each food category and is inputted into the
LSI
The following is an example of how the AH Sensor
Works:
3. Sensor detects moisture and h umidity and
lates cooking time and va riable power level.
calcu-
Cooking Sequence
1. Touch SENSOR REHEAT pad.
Note: The oven should not be operated in either mode
immediately after plugging in the unit. Wait five
minutes before cooking in sensor mode.
2. The coil to the shut off relay (RY-1) is energized, the
oven lamp, turntable motor and cooling fan motor are
turned on and the power transformer remains off.
1. Potatoes at room temperature
Vapor is emitted very slowly.
2.
Heated potatoes . Moisture and humi
rapidly.
You can
smell the aroma as it cooks.
dity is emitted
3. After about 16 seconds, the cook relay (RY-2) is energized. The power transformer is turned on, microwave energy is produced and first stage cooking is
started.
Note: The 16 second delay is for cooling time required
to remove any vapor from the oven cavity and
sensor. During this first stage, do not open the
oven door or touch the STOP/CLEAR pad.
4.
When the sensor detects the vapor emitted from the
food, the display switches over the remaining cook-
ing time and the timer counts down to zero.
At this time, the door may be opened to stir food, turn
it or season, etc.
When the timer reaches zero, an audible signal
5.
sounds. The shut-off relay and cook relay are de-energized and the power transformer, oven lamp, etc.
are turned off.
6.
By opening the door or touching the STOP/CLEAR
pad, the time of day will re-appear on the display and
the oven will revert to an OFF condition.
R-420BK
R-420BW
DESCRIPTION AND FUNCTION OF COMPONENTS
Cooling Fan Motor
The cooling fan motor drives a blade which draws external cool air. This cool air is directed through the air
vanes surrounding the magnetron to cool 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 exhaust vents in the
oven cavity.
Oven Temperature Fuse
The oven temperature fuse located on the top of the
oven cavity is designed to prevent damage to the unit if
the foods 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 oven temperature fuse re-
mains closed. However, when abnormally high temperatures are reached within the oven cavity, the fuse will
open at 144OC, causing the oven to shut down.
Note: This is a fuse and it does not reset.
Magnetron Temperature Fuse
The magnetron temperature fuse located on top of the
magnetron duct is designed to prevent damage to the
magnetron if an over heated condition develops in the
tube due to cooling fan failure, obstructed air ducts, dirty
or blocked air intake, etc.
Under normal operation, the magnetron temperature
fuse remains closed. However, when abnormally high
temperatures are reached within the magnetron the
fuse will open at 144OC, causing the oven to shut down.
Note: This is a fuse and it does not reset.
Monitor Switch
The monitor switch is activated (the contacts opened) by
the latch head on the door while the door is closed. The
switch is intended to render the oven inoperative by
means of blowing the monitor fuse when the contacts of
the primary interlock relay and secondary interlock
switch fail to open when the door is opened.
Monitor Switch Functions
When the door is opened, the monitor switch contacts close (to the ON condition) due to their being
normally closed. At this time the primary interlock
relay and secondary interlock switch are in the OFF
condition (contacts open) due to their being normally
open contacts.
When the door is closed, the monitor switch contacts
are first opened and then the door sensing switch
and the secondary interlock switch contacts close.
Note: When opening the door, each of these
switches operate inversely.
If the door is opened and the primary interlock relay
and secondary interlock switch contacts fail to open,
the monitor fuse blows simultaneously with closing
of the monitor switch contacts.
Before replacing a blown monitor fuse, test the primary interlock relay, door sensing switch, monitor switch
and secondary interlock switch for proper operation.
(Refer to section “Test Procedures”.)
l
Door Open Mechanism
The door is opened by pushing the open button on the
control panel.
When the open button is pushed, the open button
pushes up the switch lever, and then the switch lever
pushes up the latch heads.
The latch heads are moved upward and released from
the latch hook. Now the door will open.
Door Sensing / Secondary Interlock
Switches
The secondary interlock switch is mounted in the lower
position of the latch hook and the door sensing switch in
the primary interlock system is mounted in the upper
position of the latch hook. They are activated by the
latch heads on the door. When the door is opened, the
switches interrupt the circuit to all components, except
the oven lamp. A cook cycle cannot take place until the
door is firmly closed thereby activating both interlock
switches. The primary interlock system consists of the
door sensing switch and the primary interlock relay located on the control panel circuit board.
NOTE:
Latch
Heads
Monitor
Switch
Secondary
Interlock
Switch
MONITOR FUSE AND MONITOR SWITCH
ARE REPLACED AS AN ASSEMBLY.
R-420BK
R-420BW
SERVICING
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 will be found in the “Test Procedure” section.
Before replacing a blown monitor fuse, test the door sensing switch, primary interlock relay, sec-
ondary interlock switch and monitor switch for proper operation.
tion.)
Whenever troubleshooting is performed, the power supply must be disconnected. In some cases it may be necessary to connect the power supply after the outer case cabinet has been removed. In this event,
Disconnect the power supply cord, and then remove outer case cabinet.
1.
2. Open the door and block it open.
3. Discharge the high voltage capacitor.
Disconnect the leads to the primary of the power transformer.
4.
5. Ensure that the leads remain isolated from other components and oven chassis by using insulated tape.
6. After the above procedure install the outer case cabinet, reconnect the power supply cord.
When the testing is completed
1. Disconnect the power supply cord, and then remove outer case
2. Open the door and block it open.
3. Discharge the high voltage capacitor.
Reconnect the leads to the primary of the power transformer.
4.
5. Re-install the outer case (cabinet).
6. Reconnect the power supply cord after the outer case is insta
7. Run the oven and check all functions.
led.
(Refer to “Test Procedure” sec-
Troubleshooting Guide
Off Condition
Problem
Home fuse blows when power cord is
plugged into the wall receptacle.
Monitor fuse blows when power is applied.
Display does not illuminate when Shorted or open wiring
power cord is plugged in.
Display does not operate properly Primary interlock relay or door sens- Procedure E
when STOP/CLEAR button is ing switch
touched.
Oven lamp does not light with door Shorted or open wiring
opened.
Shorted power cord or wire harness
Shorted power cord or wire harness
Secondary interlock or monitor
switch
Monitor switch or monitor fuse
Oven temperature fuse
1 Control unit
Control unit
Key unit unit Procedure K
Monitor fuse
Oven temperature fuse
Oven lamp or socket
Control unit
Relay (RYI)
Possible Cause
Check or replace
Check or replace
Procedure E
Check or replace
Procedure E
Procedure F
1 Procedure G
Procedure G
Check or replace
Procedure E
Procedure F
Check or replace
Procedure G
Procedure H
Test Procedure
I
9
_---
R-420BK
R-420BW
Problem
Iven lamp does not light at all.
>ven lamp lights, but fan motor and
urntable motor do not operate.
Iven does not go into cook cycle
yhen START button is touched.
&en seems to be operating but
ittle or no heat is produced in oven
oad. (incompletely cooked or not
zooked at all at the end of cook
cycle.)
3ven goes into a cook cycle but extremely uneven heating is produced
In oven load (food).
Oven does not cook properly when
programmed for Cooking Power
P-50 (MED.) mode. (Operates
properly on Cooking Power P-HI
(HIGH) mode.)
Oven goes into COMPU DEFROST
but food is not defrosted well
The oven is in the sensor cooking
condition but AH sensor does not end
or AH sensor turns off about a maxi-
mum of 30 minutes after start.
When a cup of water is heated by
sensor, the oven does not shut off
when the water is boiling.
Troubleshooting Guide
Cook Condition
Possible Cause
Shorted or open wiring
Oven lamp or socket
Control unit
Shorted or open wiring
Cooling fan motor
Turntable motor
Shorted or open wiring
Primary interlock system
Monitor fuse
Magnetron or oven temperature
fuse
I
qelay (RYI)
t
\
-’
Shorted or open wiring
Vlagnetron
‘ower transformer
qectifier assembly
-I .V. capacitor
Primary interlock system
Shorted or open wiring
Turntable motor
Low voltage
Ditty oven cavity
wrong operation
Shorted or open wiring
Control unit
Magnetron
Wrong operation
Low voltage
Dirty oven check
Compu Defrost
Control Unit
AH Sensor
Test Procedure
Check or replace
Check or replace
Procedure G
Check or replace
Check or replace
Check or replace
Check or replace
Procedure E
Procedure E
Procedure F
Procedure H
Check or replace
Procedure A
Procedure B
Procedure C
Procedure D
Procedure E
Check or replace
Check or replace
Check _
Check
Check
Check or replace
Procedure G
Procedure A
Check
Check
Check
Procedure J
Procedure G
Procedure L
10
TEST PROCEDURES
R-420BK
R-420BW
Procedure Letter
A. Magnetron Assembly Test
1. Disconnect the power supply cord, and then remove outercase cabinet.
2. Open the door and block it open.
3. Discharge the high voltage capacitor.
4. To test for an open filament, isolate the magnetron from the high voltage circuit. A continuity check
across the magnetron filament leads should indicate less than IQ.
5. To test for a shorted magnetron, connect the ohmmeter leads between the magnetron filament
leads and chassis ground. This test should indicate an infinite resistance. If there is little or no
resistance, the magnetron is grounded (shorted) and must be replaced.
6. Reconnect all leads removed from components during testing.
7. Re-install the outercase cabinet.
8. Reconnect the power supply cord after installing the outer case cabinet.
9. Run the oven and check all functions.
MICROWAVE OUTPUT POWER
The following test procedure should be carried out with the microwave oven in a fully assembeled
condition (outer case fitted).
HIGH VOLTAGES ARE PRESENT DURING THE COOK CYCLE, SO EXTREME CAUTION
SHOULD BE OBSERVED
Power output of the magnetron can be measured by performing a water temperature rise test. This
test should only be used if above tests do not indicate a faulty magnetron and there is no defect in
the following components or wiring: high voltage rectifier, high voltage capacitor and power transformer. This test will require a 16 oz. (453~~) measuring cup and an accurate mercury thermometer
or thermocouple type temperature tester. For accurate results, the following procedure must be fol-
lowed:
Fill the measuring cup with 16 oz. (453~~) of tap water and measure the temperature of the water
1.
with a thermometer or thermocouple temperature tester. Stir the thermometer or thermocouple
through the water until the temperature stabilizes. Record the temperature of the water.
Place the cup of water in the oven. Operate oven on HIGH selecting 62 seconds cook time. Allow
2.
the water to heat.
Remove the cup from the oven and again measure the temperature, making sure to stir the ther-
3.
mometer or thermocouple through the water until the maximum temperature is recorded.
4.
Subtract the cold water temperature from the hot water temperature. The normal result should
be 38” to 78°F (21 O to 42.6”C) rise in temperature. If the water temperatures are accurately measured and are tested for the required time period the test results will indicate if the magnetron tube
has low power output (low rise in water temperature) which would extend cooking time or high
power output (high rise in water temperature) which would reduce cook time. Because cooking
time can be adjusted to compensate for power output, the magnetron tube assembly should be
replaced only if the water temperature rise test indicates a power output well beyond the normal
limits. The test is only accurate if the power supply line voltage is 120 volts and the oven cavity
Component Test
. Power Transformer
B
1. Disconnect the power supply cord, and then remove outer case cabinet.
2. Open the door and block it open.
3. Discharge the high voltage capacitor.
4. Disconnect the primary input terminals and measure the resistance of the transformer with an ohmmeter. Check for continuity of the coils with an ohmmeter. On the R X 1 scale, the resistance of
the primary coil should be less than 1 Q and the resistance of the high voltage coil should be approx-
imately 1 OOQ; the resistance of the filament coil should be less than IQ.
5. Reconnect all leads removed from components during testing.
6. Re-install the outercase cabinet.
7. Reconnect the power supply cord after installing the outer case cabinet.
8. Run the oven and check all functions.
Note: High voltages are present at the high voltage terminal, so do not attempt to measure the fila-
ment and high voltage.
11
R-420BK
R-420BW
Procedure Letter Component Test
C . High Voltage Rectifier Test
I. Disconnect the power supply cord, and then remove outer case cabinet.
2. Open the door and block it open.
3. Discharge the high voltage capacitor.
4. Isolate the rectifier from the circuit. Using the highest ohm scale of the meter, read the resistance
across the terminals and observe, reverse the leads to the rectifier terminals and observe meter
reading. If a short is indicated in both directions, or if an infinite resistance is read in both directions,
the rectifier is probably defective and should be replaced.
5. Reconnect all leads removed from components during testing.
6. Re-install the outer case cabinet.
7. Reconnect the power supply cord after installing the outer case cabinet.
8. Run the oven and check all functions.
Note: Be sure to use an Ohm-Meter that will supply a forward bias voltage of more than 6.30 Volts.
.
D
High Voltage Capacitor Test
(Discharge the high voltage capacitor before touching any oven components or wiring.)
1. Disconnect the power supply cord, and then remove outercase.
2. Open the door and block it open.
3. Discharge the high voltage capacitor.
4 If the capacitor is open, no high voltage will be available to the magnetron. Disconnect input leads
and check for short or open between the terminal using an ohmmeter.
Checking with a high ohm scale, if the high voltage capacitor is normal, the meter will indicate continuity initially and once the capacitor is charged an open circuit.
If the above is not the case, check the capacitor with an ohmmeter to see if it is shorted between
each terminal and case. If it is shorted, replace the capacitor.
5. Reconnect all leads removed from components during testing.
6. Re-install the outercase (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
E
.
Secondary Interlock Switch Test
1. Disconnect the power supply cord, and then remove outercase.
2. Open the door and block it open.
Discharge the high voltage capacitor.
Isolate the switch and connect the ohmmeter to the common (COM) and normally open (NO) terminal of the switch. The meter should indicate an open circuit with the door open and a closed circuit
with the door closed. If improper operation is indicated, replace the secondary interlock switch.
Reconnect all leads removed from components during testing.
Re-install the outercase (cabinet).
,‘. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
Primary Interlock System Test
Door Sensing Switch
1.
Disconnect the power supply cord, and then remove outercase.
2.
Open the door and block it open.
3.
Discharge the high voltage capacitor.
4.
Isolate the switch and connect the ohmmeter to the common (COM) and normally open (NO) terminal of the switch. The meter should indicate an open circuit with the door open and a closed circuit
with the door closed. If improper operation is indicated, replace the door sensing switch.
Reconnect all leads removed from components during testing.
5.
Re-install the outercase (cabinet).
6.
7
/. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
12
Procedure Letter Component Test
R-420BK
R-420BW
E.
Continued
Primary Interlock Relay CRY-2)
1. Disconnect the power supply cord, and then remove outer case cabinet.
2. Open the door and block it open.
3. Discharge the high voltage capacitor.
4. Disconnect two (2) wire leads from the relay on the printed circuit board in the control panel assembly. The relay is located on the bottom portion of the circuit board on the backside of the control
panel assembly. Connect an ohmmeter to the male terminals and observe the meter reading. The
relay contacts should be open. If the relay contacts are closed, replace the primary interlock relay
or the circuit board.
5. Reconnect all leads removed from components during testing.
6. Re-install the outer case cabinet.
7. Reconnect the power supply cord after installing the outer case cabinet.
8. Run the oven and check all functions.
Monitor Switch Test
1. Disconnect the power supply cord, and then remove outer case cabinet.
2. Open the door and block it open.
Discharge the high voltage capacitor.
3.
4
Disconnect the oven from the power supply.
Before performing this test, make sure that the secondary interlock switch and primary interlock
relay are operating properly referring to the above Switch Test Procedure.
Disconnect the wire lead from the monitor switch (NC) terminal.
Check the monitor switch operation by using the ohmmeter as follows:
When the door is open, the meter should indicate a closed circuit.
With the door open, take a screw driver and push in the monitor switch actuator located through
the lower latch hole on the faceplate of the cavity. The meter should indicate a open circuit.
If improper operation is indicated, the monitor switch may be defective and should be replaced.
After testing the monitor switch, reconnect the wire lead to the monitor switch (NC) terminal and
check continuity of the monitor circuit.
Reconnect all leads removed from components during testing.
5.
Re-install the outer case cabinet.
6.
Reconnect the power supply cord after installing the outer case cabinet.
7.
8. Run the oven and check all functions.
Red Wire
Connected to
Normally Closed Terminal
Note1 : Connect ohmmeter
probes here.
Note2: Use screwdriver to engage
monitor switch actuator.
13
WhiteWires
Connected to
Common Terminal
Monitor Switch
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