Sharp R21lcf Service Manual

							
R21LCF
6 – 3
3) If the door is opened, and the primary interlock relay (RY1) andsecondary interlock switch contacts fail to open, the monitor fuse
blows simultaneously with closing  of the monitor switch contacts.
CAUTION: BEFORE REPLACING  A BLOWN MONITOR FUSE TEST
THE DOOR SENSING SWITCH, PRIMARY INTERLOCK
RELAY (RY1), SECONDARY INTERLOCK SWITCH AND
MONITOR SWITCH FOR PROPER OPERATION. (REFER
TO CHAPTER TEST PROC
NOTE: MONITOR FUSE AND MONITOR SWITCH ARE REPLACED
AS AN ASSEMBLY.
4. ANTENNA MOTOR
The antenna motor rotates the stirrer antenna located on the bottom of
the oven cavity, so that the food on the ceramic shelf is cooked evenly
during cooking. The antenna motor may turn in either direction.
5. 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 magne-
tron and cools the magnetron. This  air is channelled through the oven
cavity to remove steam and vapors given off from the heating food. It
is then exhausted through the exhausti ng air vents at the oven cavity.
6. MONITOR FUSE
1) The monitor fuse blows when the contacts (COM-NO) of the pri-
mary interlock relay (RY1) and secondary interlock switch remain
closed with the oven door open and when the monitor switch
closes.
2) If the wire harness or electrical components are shortcircuited, this monitor fuse blows to prevent an  electric shock or fire hazard.
7. THERMAL CUT-OUT 145 °C (MAGNETRON)
This thermal cut-out protects the magnetron against overheating. If the
temperature goes up higher than 293 °F (145 °C) because the fan
motor is interrupted or the ventilat ion openings are blocked, the ther-
mal cut-out will open and line voltages to the high voltage transformer
will be cut off and the operation of the magnetron will be stopped. The
thermal cutout will not resume.
8. 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 catches fire due
to over heating produced by improper  setting of the cooking time or
failure of control unit. Under normal operation, the oven thermal cut-
out remains closed. However, when abnormally high temperatures are
reached within the oven cavity, t he oven thermal cut-out will open at
257 °F(125 °C) causing the oven to shut down. The thermal cut-out will
not resume.
9. NOISE FILER
The noise filter prevents the radio frequency interference that might
flow back in the power circuit.  
						

							
R21LCF
7 – 1
R21LCFService Manual CHAPTER 7. TROUBLESHOOTING GUIDE 
When troubleshooting the microwave oven, it is helpful to follow the Sequence of Operation in performing the checks. Many of th e possible causes of
trouble will require that a specific test  be performed. These tests are given a proc edure letter which will be found in the Test Procedure section.
IMPORTANT:
If the oven becomes inoperative because of a blown monitor fuse,
check the monitor switch, primary in terlock relay (RY1), door sensing
switch and secondary interlock switch before replacing the monitor
fuse. If monitor fuse is replaced, the monitor switch must also be
replaced. Use part FFS-BA033WRKZ as an assembly.
IMPORTANT:
Whenever troubleshooting is performed with the power supply cord
disconnected. It may in, some cases, be necessary to connect the
power supply cord after the outer case has been removed, in this
event,
1) Disconnect the power supply cord, and then remove outer case.
2) Open the door and block it open.
3) Discharge high voltage capacitor. 4) Disconnect the leads to the primary of the power transformer.
5) Ensure that the leads remain isolated from other components and
oven chassis by using insulation tape.
6) After that procedure, 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 high voltage capacitor.
4) Reconnect the leads to the primary of the power transformer.
5) Reinstall the outer case (cabinet).
6) Reconnect the power supply cord after the outer case is installed.
7) Run the oven and check all functions.
[1] TROUBLESHOOTING CHART 
Never touch any part in the circuit with your hand or  an uninsulated tool while the power supply is connected.
TE S T PR OCE DUR E
C ONDIT IONPROBLEMPOSSIBLE CASE
AND
DE F E C T IV E P AR T S
H ome fus e or circuit brea ker blows when
powercordis pluggedintowalloutlet.
Monitor fus e blows whe n powe r c ord is
plugge d into wa ll outle t.
O ve n la mp doe s not light, a nd fa n motor
a nd a nte nna motor do not ope ra te .
Oven does not go into cook cycle when
Light Up Dial turned.
Oven seems to be operating but little or
no hea t is produced in oven loa d. (F ood
incompletely cooked or not cooked a t a ll
at end of cook cycle.)
Oven goes into a cook cycle but
extremely uneven heating is produced in
oven loa d (food).
OFF
CONDITION
C OOKING
CONDITION
MAG NE T R O N
POWER TRANSFORMER
H.V . R E C T IF IE R AS S E MB LY
HIG H V OLT AG E C AP AC IT OR
THE R MAL C UT-OUTS E C ONDAR Y INTE R LOC K S WITC HPRIMARY INTERLOCK SYSTEM
MO NIT O R S W IT C H
MO NIT O R F US E
NOIS E F ILT E R
CONTROL PANEL
RELAY (RY2)
FOIL PATTUR N ON P.W.B.
LOW VOLTAGE WR ONG OPE R ATION
DIR T Y OV E N C AV IT Y SHORTED IN POWER CORD OVE N LAMP OR S OC KE T
C OOLING FAN MOTOR
ANTE NNA MOTOR
S HOR T OR OP E NE D W IR ING
ABCDE FFGHI J KLRE RE RE RE RECK CK CK 
						

							
R21LCF
8 – 1
R21LCFService Manual CHAPTER 8. TEST PROCEDURES
[1] Procedure A: MAGNETRON ASSEMBLY TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge 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 1 ohm.
5. To test for a shorted magnetron, connect the ohmmeter leads bet ween 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 and must be replaced.
6. Reconnect all leads removed from components during testing.
7. Reinstall the outer case (cabinet).
8. Reconnect the power supply cord after the outer case is installed.
9. Run the oven and check all functions.
1. MICROWAVE OUTPUT POWER
The following test procedure should be carried out with the microw ave oven in a fully assembled condition (outer case fitted).
HIGH VOLTAGES ARE PRESENT DURING THE COOK CY CLE, SO EXTREME CAUTION SHOULD BE OBSERVED.
Power output of the magnetron can be measured by performing a wa ter temperature rise test. This test should only be used if above tests do not indi-
cate a faulty magnetron and there is no defect in the following  components or wiring: silicon rectifier, high voltage capacitor and power transformer.
This test will require a 16 ounc e (453cc) measuring cup and an accurate mercury  thermometer or thermocouple type temperature tester. For accurate
results, the following procedure must be followed carefully:
1. Fill the measuring cup with 16 oz. (453cc) of tap water and measure the temperature of the water with a thermometer or thermo couple tempera-
ture tester. Stir the thermometer or thermocouple through the water until the temperature stabilizes. Record the temperature of  the water.
2. Place the cup of water in the oven. Operate oven at full power  selecting more than 60 seconds cook time. Allow the water to heat for 60 seconds,
measuring with a stop watch, second hand of a watch or the digital read-out countdown.
3. Remove the cup from the oven and again measure the temperature,  making sure to stir the thermometer 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 34.7 to 64.6 °F(19.3 to 35.9 °C) rise in tempera-
ture. If the water temperatures are accurately measured and 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 woul d extend cooking time or high power output (high rise in water temperature) which
would reduce cooking time. Becaus e cooking time can be adjusted to compensate fo r power output, the magnetron tube assembly sho uld be
replaced only if the water temperature rise test indicates a pow er output well beyond the normal limits. The test is only accurate if the power supply
line voltage is 120 volts a nd the oven cavity is clean.
[2] Procedure B: POWER TRANSFORMER TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge 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 co il should be less than 1 ohm and the resistance of the high voltage coil should be
approximately 83.7 ohms; the resistance of t he filament coil should be less than 1 ohm.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
(HIGH VOLTAGES ARE PRESENT AT THE HIGH VOLTAGE TERMINAL,  SO DO NOT ATTEMPT TO MEASURE THE FILAMENT AND HIGH
VOLTAGE.)
[3] Procedure C: HIGH VOLTAGE RECTIFIER TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Isolate the rectifier from the circuit.  Using the highest ohm scale of the meter,  read the resistance across the terminals an d observe, reverse the
leads to the rectifier terminals and observe meter reading. If a s hort is indicated in both directions, or if an infinite resistance is read in both direc-
tions, the rectifier is probably  defective and should be replaced.
5. Reconnect all leads removed from components during testing. 
						

							
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8 – 2
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
NOTE:Be sure to use an ohmmeter that will supply a forward bias voltage of more than 6.3 volts.
[4] Procedure D: HIGH  VOLTAGE CAPACITOR TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge 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 o pen between the termi-
nals using an ohmmeter.
Checking with a high ohm scale, if the high voltage capacitor is nor mal, the meter will indicate continuity for a short time an d should indicate an
open circuit once the capacitor is charged.  If the above is not the case, check the capa citor with an ohmmeter to see if it is shorted between either
of the terminals and case. If it is shorted, replace the capacitor.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
[5] Procedure E: TH ERMAL CUT OUT TEST
1. THERMAL CUT OUT 125 °C (OVEN)
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. A continuity check across the thermal cu t-out terminals should indicate a closed circuit unless the temperature of the therma l cut-out reaches
approximately 257 °F(125 °C). An open thermal cut-out indicates overheating of the  oven, exchange the thermal cut-out and check inside of oven
cavity and for improper setting of cooking  time or operation of control unit. Check for restricted air flow through the vent holes of the oven cavity,
especially the cooling fan and air guide.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
2. THERMAL CUT OUT 145 °C (MAGNETRON)
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. A continuity check across the thermal cu t-out terminals should indicate a closed circuit. If the temperature of the magnetron  reaches approximately
293 °F(145 °C), the thermal cut-out opens. An open thermal cutout indicates ov erheating of the magnetron. Check for restricted air flow to the mag-
netron, especially the  cooling fan air guide.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
CAUTION: IF THE THERMAL CUT-OUT INDICATES AN OPEN CIRCUIT AT ROOM TEMPERATURE, REPLACE THERMAL CUT-OUT.
[6] Procedure F: SECONDAR Y INTERLOCK SWITCH TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge 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 sho uld 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.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet). 
						

							
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8 – 3
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
[7] Procedure F: PRIMARY INTERLOCK SYSTEM TEST
1. DOOR SENSING SWITCH
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge 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 sho uld 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.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
NOTE: If the door sensing switch contacts fail in the open po sition and the door is closed, the cooling fan, antenna and oven li ght will be activated by
RY1.
2. PRIMARY INTERLOCK RELAY (RY1)
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect two (2) wire leads from the male tab terminals of  the Primary Interlock Relay. Check the state of the relay contacts using a ohmmeter.
The relay contacts should be open. If the relay contacts are cl osed, replace the circuit board entirely or the relay itself.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
[8] Procedure G: MONITOR SWITCH TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Before performing this test, make sure that the secondary in terlock switch and the primary interlock relay are operating prop erly, according to the
above Switch Test Procedure. Disconnect the wire lead from the m onitor switch (COM) terminal. Check the monitor switch operation by using the
ohmmeter as follows. When the door is open, the meter should indica te a closed circuit. When the monitor switch actuator is pushed by a screw
driver through the lower latch hole on the front plate of t he oven cavity with the door opened (in this condition the plunger of the monitor switch is
pushed in), the meter should indicate an open circuit. If improper  operation is indicated, the switch may be defective. After testing the monitor
switch, reconnect the wire lead to the monitor switch (COM)  terminal and check the continuity of the monitor circuit.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
[9] Procedure H: BLOWN MINITOR FUSE TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
SCREW
DRIVER MONITOR
SWITCH
OHMMETER
WHT/ WHT 
						

							
R21LCF
8 – 4
3. Discharge high voltage capacitor.
4. If the monitor fuse is blown when the door is opened, check the primary interlock relay, secondary interlock switch and monitor switch according to
the TEST PROCEDURE for those switches  before replacing the blown monitor fuse.
CAUTION: BEFORE REPLACING A BLOWN MONITO R FUSE, TEST THE PRIMARY INTERLOCK RELAY, SECONDARY INTERLOCK SWITCH,
DOOR SENSING SWITCH AND MONITOR SWITCH FOR PROPER OPERATION.
If the monitor fuse is blown by improper switch operation, the mo nitor fuse and monitor switch must be replaced with monitor fuse and monitor
switch assembly part number FFS-BA033WRKZ, even if the monitor  switch operates normally. The monitor fuse and monitor switch assembly is
comprised of a 20 ampere fuse and switch.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
[10] Procedure I:  NOISE FILTER TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect the lead wires from the termi nal  the noise filter. Using an ohmmeter,
check between the terminals as described in  the following table. If incorrect reading
are obtained, replace the noise filter.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
[11] Procedure J: CONTROL PANEL ASSEMBLY TEST
WARNING: To prevent an electric shock do not  touch the electrical parts and the printed wiring board. Because the control unit i s “TRANSLESS CIR-
CUIT” and many electrical part s are used at A.C. line voltage.
The control panel consists of circuits incl uding semiconductors such as LSI, ICs, etc.  Therefore, unlike conventional microwave  ovens, proper main-
tenance cannot be performed with only a voltmeter and ohmmeter. In  this service manual troubleshooting by unit replacement is described according
to the symptoms indicated.
1) Disconnect the power supply cord and then remove outer case.
2) Open the door and block it open.
3) Discharge high voltage capacitor. 
4) Disconnect the leads to the primary of the power transformer.
5) Ensure that these leads remain isolated from ot her components and oven chassis by using insulation tape.
6) After that procedure, re-connect the power supply cord.
1. Control Unit.
The following symptoms indicate a defective control unit. 
1) In connection with LEDs a) At a certain LED, all or some LEDs do not light up.
b) At a certain LED, brightness is low.
c) Only one LED does not light up. 
d) All or some LEDs continue to light up.
e) A certain group of LEDs do not light up.
f) The LEDs flicker.
2) Other possible problems caused  by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Cooking is not possible.
c) Cooking time can not be set. MEASURING POINT INDICATION OF OHMMETER 
Between N and L Open circuit.
Between terminal N and WHITE Short circuit.
Between terminal L and RED Short circuit.
FUSE
LINE CROSS CAPACITOR 0.22μF AC250V
WHITE RED NOISE SUPPRESSION COIL
LINE BYPASSCAPACITOR
0.0033μF / AC 250V
LINE BYPASS
CAPACITOR
0.0033μF / AC 250V 20A
NOISE FILTER
NL 
						

							
R21LCF
8 – 5
When testing is completed,
1) Disconnect the power supply cord and then remove outer case.
2) Open the door and block it open.
3) Discharge high voltage capacitor. 
4) Reconnect all leads removed from components during testing.
5) Re-install the outer case (cabinet).
6) Reconnect the power supply cord after the outer case is installed.
7) Run the oven and check all functions.
[12] Procedure L: RELAY TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect the leads to the primary of the power transformer.
5. Ensure that these leads remain isolated from other components and oven chassis by using insulation tape. 
6. After that procedure, re-connect the power supply cord.
7. Remove the outer case and check voltage between Pin No. 5 of t he 3 pin connector (A) and the common terminal of the relay RY1 on the control
unit with an A.C. voltmeter.
The meter should indicate 120 vo lts, if not check oven circuit.
RY1 and RY2 Relay Test
These relays are operated by D.C. voltage
Check voltage at the relay coil with a D.C.  voltmeter during the microwave cooking operation.
       DC. voltage indicated ................. Defective relay.
       DC. voltage not indicated ........... Check diode which is  connected to the relay coil. If diode is good, control unit is defective.
NOTE: The voltage under the condition when all LEDs light up.
8. Disconnect the power supply cord and then remove outer case.
9. Open the door and block it open.
10.Discharge high voltage capacitor.
11. Reconnect all leads removed from components during testing.
12.Re-install the outer case (cabinet).
13.Reconnect the power supply cord after the outer case is installed.
14.Run the oven and check all functions.
[13] Procedure M: FOIL PATTERN  ON THE PRINTED WIRING BOARD TEST
To protect the electronic circuits, this mo del is provided with a fine foil pattern adde d to the primary on the PWB, this foil pattern acts as a fuse.
1. Foil pattern check and repairs.
1) Disconnect the power supply cord and then remove outer case.
2) Open the door and block it open.
3) Discharge high voltage capacitor.
4) Follow the troubleshooting guide given below for repair. 
5) Make a visual inspection of the varistor. Check for burned damage.
6) Reconnect all leads removed from components during testing.
7) Re-install the outer case (cabinet).
8) Reconnect the power supply cord after the outer case is installed.
9) Run the oven and check all functions. RELAY SYMBOL OPERATIONAL VO
LTAGE CONNECTED COMPONENTS
RY1 Approx. 19.2V D.C. Oven lamp / Antenna motor / Cooling fan motor
RY2 Approx. 19.9V D.C. Power transformer
STEPS OCCURRENCE CAUSE OR CORRECTION 1 Only pattern at “a” is broken. *Insert jumper wire J1 and solder.
2 Pattern at “a” and “b” are broken. *Replace control unit.
RY2
RY1
J1 CNA
VR S 1 5
b
d
c a 
						

							
R21LCF
8 – 6
2. Follow the troubleshooting guide given below, if indicator does not light up after above check and repairs are finished.
1) Disconnect the power supply cord and then remove outer case.
2) Open the door and block it open.
3) Discharge high voltage capacitor.
4) Disconnect the leads to the primary of the power transformer.
5) Ensure that these leads remain isolated from ot her components and oven chassis by using insulation tape.
6) After that procedure, re-connect the power supply cord.
7) Follow the troubleshooting guide given below for repair.
8) Disconnect the power supply cord and then remove outer case.
9) Open the door and block it open.
10)Discharge high voltage capacitor.
11)Reconnect all leads removed from components during testing.
12)Re-install the outer case (cabinet).
13)Reconnect the power supply cord after the outer case is installed.
14)Run the oven and check all functions. STEPS OCCURRENCE CAUSE OR CORRECTION
1 The rated AC voltage is not present between Pin No. 5 of the 3-pin connector (A) 
and the common terminal of the relay RY1.
Check supply voltage and oven power cord. 
						

							
R21LCF
9 – 1
R21LCFService Manual CHAPTER 9. TOUCH CONTROL PANEL ASSEMBLY
[1] OUTLINE OF TOUCH CONTROL PANEL 
1. Control Unit 
Control unit consists of LSI, power source circuit, synchronizing signal
circuit, reset circuit, buz zer circuit, encoder circui t and indicator circuit.
1) LSI
This LSI controls the encoder si gnal, relay driving signal for oven
function, buzzer signal and LED signal.
2) Power Source Circuit This circuit generates voltage necessary in the control unit. 
Symbol Voltage Application
VC +5V (*) LSI(I-1)
VR +20V (*) RELAY(RY1, RY2)
(*) The voltage under the condition when all LEDs light up. The
voltage VR will vary according to the quantity of the LEDs which
light up
3) Synchronizing Signal Circuit
The power source synchronizing signal  is available in order to com-
pose a basic standard time in the clock circuit. It accompanies a
very small error because it works on commercial frequency. 4) Reset Circuit
A circuit to generate a signals which  resets the LSI to the initial
state when power is supplied.
5) Buzzer Circuit The buzzer is responsive to signa ls from the LSI to emit audible
sounds (completion sound).
6) Door Sensing Switch
A switch to “tell” the LSI if the door is open or closed.
7) Relay Circuit
To drive the magnetron, fan motor, antenna motor and light the
oven lamp.
8) Encoder The encoder generates the pulse signal, and the pulse signal is
sent to the LSI.
9) Indicator Circuit Indicator elements are the Light- emitting diodes (LD1- LD20).
This circuit consists of 4-digits and 5 segments. 
[2] SERVICING FOR TOUCH CONTROL PANEL
1. Precautions for Handling Electronic Components
This unit uses CMOS LSI in the integral part of the circuits. When han-
dling these parts, the following pr ecautions should be strictly followed.
CMOS LSI have extremely high impedance at its input and output ter-
minals. For this reason, it is  easily influenced by the surrounding high
voltage power source, static electr icity charge in clothes, etc., and
sometimes it is not fully protecte d by the built-in protection circuit.
In order to protect CMOS LSI.
1) When storing and transporting, thoroughly wrap them in aluminium foil. Also wrap PW boards contai ning them in aluminium foil.
2) When soldering, ground the tec hnician as shown in the figure and
use grounded soldering iron and work table.
2. Servicing of Touch Control Panel
We describe the procedures to perm it servicing of the touch control
panel of the microwave oven and the precautions you must take when
doing so. To perform the servicing, power to the touch control panel is
available either from the power line  of the oven itself or from an exter-
nal power source.
1. Servicing the touch control panel with power supply of the oven:
CAUTION: THE HIGH VOLTAGE  TRANSFORMER OF THE MICRO-
WAVE OVEN IS STILL LIVE DURING SERVICING AND
PRESENTS A HAZARD.
Therefore, before checking the performance of the touch control
panel,
1) Disconnect the power supply cord and then remove outer case.
2) Open the door and block it open.
3) Discharge high voltage capacitor.
4) Disconnect the leads to the pr imary of the power transformer. 5) Ensure that these leads remain isolated from other components
and oven chassis by us ing insulation tape.
6) After that procedure, re-connect the power supply cord.
After checking the performance of the touch control panel,
1) Disconnect the power supply cord.
2) Open the door and block it open.
3) Re-connect the leads to the primary of the power transformer.
4) Re-install the outer case (cabinet).
5) Re-connect the power supply cord after the outer case is installed.
6) Run the oven and check all functions. a) On some models, the power supply cord between the touchcontrol panel and the oven itself is so short that the two cant
be separated. For those models, check and repair all the
controls (sensor-related ones in cluded) of the touch control
panel while keeping it connected to the oven.
b) On some models, the power supply cord between the touch control panel and the oven proper is so long enough that
they may be separated from each other. For those models,
therefore, it is possible to chec k and repair the controls of the
touch control panel while keeping it apart from the oven
proper; in this case you must short both ends of the door
sensing switch (on PWB) of the touch control panel with a
jumper, which brings about an ope rational state that is equiv-
alent to the oven door being closed. As for the sensor-
related controls of the touch control panel, checking them is
possible if the dummy resistor (s) with resistance equal to
that of the controls are used.
2. Servicing the touch control panel  with power supply from an exter-
nal power source:
Disconnect the touch control panel  completely from the oven
proper, and short both ends of the door sensing switch (on PWB) of
the touch control panel, which brings about an operational state
that is equivalent to the oven door being closed. 
approx. 1M ohm 
						

							
R21LCF
9 – 2
Connect an external power source to the power input terminal of
the touch control panel, then it is possible to check and repair the
controls of the touch control panel;  it is also possible to check the
sensor-related controls of the t ouch control panel by using the
dummy resistor(s).
3. Servicing Tools
Tools required to service the  touch control panel assembly.
1) Soldering iron: 60W
(It is recommended to use a soldering iron with a grounding termi-
nal.)
2) Oscilloscope: Single beam, frequency range: DC - 10MHz type or more advanced model.
3) Others: Hand tools
4. Other Precautions
1) Before turning on the power source of the control unit, remove the aluminium foil applied for pr eventing static electricity.
2) Connect the connector of the key unit to the control unit being sure that the lead wires are not twisted.
3) After aluminium foil is removed, be careful that abnormal voltage due to static electricity etc. is not applied to the input or output ter-
minals.
4) Attach connectors, electrolytic  capacitors, etc. to PWB, making
sure that all connections are tight.
5) Be sure to use specified components where high precision is required.