Sharp R-7A55 User manual

SHARP CORPORATION
SERVICE MANUAL
R-7A55(W)/(B)
R-7E45(W)/(B)
TABLE OF CONTENTS Page
CAUTION, MICROWAVE RADIATION................................................................................INSIDE COVER
WARNING....................................................................................................................................................1
PRODUCT SPECIFICATIONS ................................................................................................................... 2
GENERAL IMPORTANT INFORMATION ...................................................................................................2
APPEARANCE VIEW ................................................................................................................................. 3
OPERATION SEQUENCE.......................................................................................................................... 4
FUNCTION OF IMPORTANT COMPONENTS .......................................................................................... 6
SERVICING ................................................................................................................................................ 9
TEST PROCEDURE................................................................................................................................. 12
TOUCH CONTROL PANEL.......................................................................................................................20
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE..................................................... 25
MICROWAVE MEASUREMENT .............................................................................................................. 30
TEST DATA AT A GLANCE ..................................................................................................................... 31
WIRING DIAGRAM................................................................................................................................... 32
PICTORIAL DIAGRAM ............................................................................................................................. 35
CONTROL PANEL CIRCUIT .....................................................................................................................36
PRINTED WIRING BOARD .......................................................................................................................38
PARTS LIST ............................................................................................................................................. 39
In interests of user-safety the oven should be restored to its original
condition and only parts identical to those specified should be used.
SY308R7A55EHW
R-7A55(W)
R-7A55(W)
R-7A55(B)
R-7E45(W)
R-7E45(B)
MODELS
GRILL AND CONVECTION
MICROWAVE OVEN

R-7A55(W)/(B)
R-7E45(W)/(B)
CAUTION
MICROWAVE RADIATION
Personnel 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.
VARNING
MICKROVAGSSTRALING
Personal får inte utsättas för mikrovågsenergi som kan ustrala från magnetronen eller
andre mikrovågsalstrande anordningar om dessa är felanslutna eller används på fel sätt.
Alla in-och utgångsanslutningar för mikrovågor, vagledare, flänsar och packningar måste
vara fast anslutna.
Mikrovågsgeneratorn får inte arbeta utan att absorberande belastning är ansluten. Titta
aldrig in i ën öppen vågledare eller antenn när mikrovågsgeneratorn är påkopplad eller
laddad.
VAROITUS
MIKROAALTOSÄTELYÄ
Käyttäjä ei saa joutua alttiiksi mikroaaltoenergialle, jota voi säteillä magnetronista tai
muusta mikroaaltoja kehittävästä laitteesta, jos sitä käytetään tai jos se kytketään väärin.
Kaikkien mikroaaltoliitäntöjen sekä syöttö-että ulostulopuolella, aaltoputkien laippojen ja
tiivisteiden tulee olla varmistettuja.
Mikroaaltouunnia ei koskaan saa käyttää ilman kuormaa jossa mikroaaltoenergiaa kuluu.
Avoimeen aaltoputkeen tai antenniin ei koskaan saa katsoa virran ollessa kytkettynä.
ADVARSEL
MIKROBØLGESTRÅLING
Personell må ikke utsettes for mikrobølge-energi som kan utståles fra magnetronen eller
andre mikrobølge-generende deler dersom apparatet feilbetjenes eller blir feiltikoplet.
Alle inn-og ut-tilkoplinger i forbindelse med mikrobølge-strålingen, bølgeledere, flenser og
tetningsringer/pakninger må festes ordentlig.
Aldri bruk apparatet med mindre en mikrobålge-absorberende last er plassert i
ovnsrommet.
Aldri se direkte inn i en åpen bølgeleder eller antenne imens apparatet er strømførende.
ADVARSEL
MIKROBØLGEBESTRÄLING
Man bør ikke udsætte sig for mikrobølgebestråling fra magnetronen eller andre
mikrobølgefrembringende anordninger, hvilket kan ske hvis apparatet er forkert tilsluttet
eller bruges forkert. Alle mikrobølgeindgange og-udgange, bølgeledere, flanger og
tætningsstrimler må være forsvarligt udført.
Anvend aldrig ovnen uden en mikrobølgesabsorberende anordning. Se aldrig ind i en
åben bølgeleder eller antenne, mens ovnen er i brug.

1
R-7A55(W)/(B)
R-7E45(W)/(B)
SHARP CORPORATION
OSAKA, JAPAN
FUNCTION OF IMPORTANT
COMPONENTS
SERVICING AND
TROUBLESHOOTING CHART
TEST PROCEDURE
GENERAL INFORMATION
APPEARANCE VIEW
OPERATING SEQUENCE
PRODUCT SPECIFICATIONS
GRILL AND CONVECTION
MICROWAVE OVEN
R-7A55(W)/ R-7A55(B)/R-7E45(W)/R-7E45(B)
GENERAL IMPORTANT INFORMATION
ThisManualhasbeenpreparedtoprovideSharpCorp.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.
WARNING
Neveroperatetheovenuntilthefollowingpointsareensured.
(A) The door is tightly closed.
(B) The door latches and hinges are not defective.
(C) The door is not deformed or warped.
(D) There is not any other visible damage with the oven.
Servicing and repair work must be carried out only by trained
service engineers.
Note: All the parts marked "∆" on the parts list may cause
unduemicrowaveexposure,bythemselves,orwhen
they are damaged, loosened or removed.
WARNING
Note: The parts marked "*" are used in volt-
age more than 250V. (Parts List)
Anm: Delar märket med "*" har en spänning
överstigande 250V.
Huom: Huolto-ohjeeseen merkitty "tähdella"
osat joissa jännite on yli 250 V.
Bemerk: Delersomermerket"asterisk"erutsatt
for spenninger over 250V til jord.
Bemærk: "Delemærketmedstjernebenyttesmed
højere spænding end 250 volt.
MICROWAVE MEASUREMENT
TEST DATA AT A GLANCE
WIRING DIAGRAM
PARTS LIST
COMPONENT
REPLACEMENT AND
ADJUSTMENT PROCEDURE
TOUCH CONTROL PANEL
SERVICE MANUAL

2
R-7A55(W)/(B)
R-7E45(W)/(B)
ITEM DESCRIPTION
Power Requirements 220-230 Volts / 50 Hertz / Single phase, 3 wire earthed
Power Consumption Microwave cooking 1.6 kW Approx. 7.5A
Dual cooking
(Microwave and Grill) 2.8kW Approx. 12.8A
(Microwave and Convection) 2.9kW Approx. 13.5A
Convection cooking 1.5kW Approx. 6.1A
Grill cooking Max. 2.55kW Approx. 11.3A
Power Output 1000 watts nominal of RF microwave energy (measured by method of IEC
705) Operating fequency 2450 MHz
Convection heating element Power Output 1.3kW
Grill heating element Power Output 1.2kW (600W x 2)
Case Dimensions Width 520 mm Height 305 mm (including foot) Depth 478 mm
Cooking Cavity Dimensions Width 342 mm Height 195 mm Depth 357 mm
Turntable diameter 325mm
Control Complement Touch Control System
Microwave Cooking Control
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
POTATO keys (R-7A55 only)
INSTANT ACTION keys (R-7A55 only)
LESS( )/MORE( ) (R-7A55 only)
DUAL COOK, GRILL, MICROWAVE, CONVECTION
MINUTE TIMER/HOLD
CLOCK SETTING, STOP
MINUTE PLUS/START
TIME KEY (10 MIN., 1MIN., 10 SEC.)
Set Weight Approx. 23 kg
PRODUCT DESCRIPTION
SPECIFICATION
GENERAL IMPORTANT INFORMATION
WARNING
THIS APPLIANCE MUST BE EARTHED
IMPORTANT
THE WIRES IN THIS MAINS LEAD ARE COLOURED IN ACCORDANCE WITH THE FOLLOWING CODE:
GREEN-AND-YELLOW : EARTH
BLUE : NEUTRAL
BROWN : LIVE

3
R-7A55(W)/(B)
R-7E45(W)/(B)
APPEARANCEVIEW
OVEN
Door
Door hinges
Grill heating elements
Oven lamp
Wave guide cover
Control panel
Coupling
Door lock openings
Oven cavity
Door seals and sealing surfaces
Safety door latches
Ventilation openings
Outer cabinet
Rear cabinets
Power supply cord
CONTROLPANEL
10
MIN
1
MIN
STOP
10
S
1 min
R-7A55
˚C
1
2
1
2
3
4
56789
10
11
12
13
14
15
18
19
21
22
24
25
16
17
20
23
DISPLAY AND INDICATORS
Check indicator after the oven parts to
confirm the oven is operating as de-
sired.
1. MORE indicator
2. LESS indicator
3. CONVECTION indicator
4. GRILL indicator
5. LOW
6. MEDIUM LOW Microwave
7. MEDIUM power level
8. MEDIUM HIGH Indicators
9. HIGH
10.Digital display
11.Units of weight indicator
12.Cook indicator
This indicator shows cooking in
progress.
OPERATING KEY
13.POTATO keys
14.INSTANT ACTION keys
15.MORE( )/LESS( ) keys
16.Time keys
17.MINUTE TIMER/HOLD key
18.CONVECTION key
19 MICROWAVE key
20.CLOCK SETTING key
21.DUAL COOK key
22.GRILL key
23.STOP key
24.MINUTE PLUS/START key
25.Door open button
R-7E45
R-7A55
10
MIN
1
MIN
STOP
10
S
1 min
R-7E45
˚C
1
2
3
4
56789
10
12
18
19
21
22
24
25
16
17 20
23

4
R-7A55(W)/(B)
R-7E45(W)/(B)
OPERATION SEQUENCE
OFF CONDITION
Closing the oven door activates all door interlock switches
(1st. latch switch, 2nd. latch switch and stop switch.
IMPORTANT:
When the oven door is closed, the contacts COM-NC of the
monitor switch SW4 must be open and the contacts (COM-
NO) must be closed. When the microwave ovenis pluged in
a wall outlet (220 - 230V / 50Hz), 220 - 230 volts A.C. is
supplied to the point H1 + H3 in the control unit.
Figure O-1 on page 32
1. The display flashes "88:88"
2. To set any programmes or set the clock, you must first
touch the STOP key.
3. " : " appears in display.
NOTE: When the oven door is opened, the oven lamp
comes on at this time.
MICROWAVE COOKING CONDITION
HIGH COOKING
EnteradesiredcookingtimewiththetouchingTimekeyand
start the oven with touching START key.
Function sequence Figure O-2 on page 32
CONNECTED COMPONENTS RELAY
Oven lamp, Fan motor, Turntable motor RY1
High voltage transformer RY1 + RY2
Fan motor RY6
1. 220-230 volts A.C. is supplied to the primary winding of
thehighvoltagetransformer.The voltageis convertedto
about 3.3 volts A.C. output on the filament winding and
high voltage of approximately 2000 volts A.C. on the
secondary winding.
2. The filament winding voltage (3.3 volts) heats the
magnetron filament and the high voltage (2000 volts) is
senttothe voltagedoublingcircuit,where itisdoubledto
negative voltage of approximately 4000 volts D.C..
3. The 2450 MHz microwave energy produced in the
magnetron generates a wave length of 12.24 cm. This
energy is channelled through the waveguide (transport
channel)intotheovencavity, wherethe foodisplacedto
be cooked.
4. When the cooking time is up, a signal tone is heard and
the relays RY1 + RY2 + RY6 go back to their home
position. The circuits to the oven lamp, high voltage
transformer, fan motor and turntable motor are cut off.
5. When the oven door is opened during a cooking cycle,
the switches come to the following condition.
Switch Contact Condition
During Oven Door
Cooking Open(No cooking)
1st latch Switch COM-NO Closed Opened
Monitor Switch COM-NO Closed Opened
Monitor Switch COM-NC Opened Closed
2nd latch switch COM-NO Closed Opened
Stop switch COM-NO Closed Opened
Thecircuittothehighvoltagetransformer,iscutoffwhenthe
contact of relay RY2 contacts COM-NO of the 1st latch
switch, and monitor switchSW4 are made open. The circuit
to the fan motor is cut off when the relayRY6 is made open.
Thecircuittothe turntablemotor iscutoffwhenthecontacts
COM-NO of the 2nd latch switch are made open. The relay
RY2and RY6 aremade openwhenthe doorisopened. The
oven lamp remains on even if the oven door is opened after
the cooking cycle has been interrupted, because the relay
RY1 stay closed. Shown in the display is remaining time.
6. MONITOR SWITCH CIRCUIT
The monitor switch SW4 is mechanically controlled by
theovendoor,andmonitorstheoperationofthe1stlatch
switch SW1.
6-1. When the oven door is opened during or after the cycle
ofacookingprogram,the1stlatchswitchSW1andstop
switch SW3 must open their contacts (COM-NO) first.
After that the contacts (COM-NC) of the monitor switch
SW4 can be closed and the contacts (COM-NO) of
monitor switch SW4 are made open, and the contacts
(COM-NO)ofthe2ndlatchswitchSW2canbeopened.
6-2. Whentheovendoorisclosed.Thecontacts(COM-NC)
of the monitor switch SW4 must be opened and the
contacts (COM-NO) of monitor switch SW4 must be
closed, and the contacts (COM-NO) of the 2nd latch
switch SW2 must be closed. After that the contacts of
the 1st latch switch SW1 and the stop switch SW3 are
made closeed.
6-3. When the oven door is opened and the contacts of the
1st latch switch SW1 remain closed, the fuseF2 F6.3A
will blow. Because the relay RY1 and monitor switch
SW4 are closed and a short circuit is caused.
CONVECTION COOKING CONDITION
PREHEATING CONDITION (Figure O-3)
ProgramdesiredconvectiontemperaturebytouchingCON-
VECTIONkey. Whenthe STARTkey istouched, the follow-
ing operations occur:
1. The coil of shut-off relays RY1 ,RY4 and RY6 are
energized, the oven lamp, cooling fan motor, turntable
motor and convection motor are turned on.
Note: The On/Off time ratio does not exactly correspond to
thepercentageofmicrowavepower,becauseapprox.
2 seconds are needed for heating up the magnetron
filament.
32 sec. ON
24 sec. ON
18 sec. ON
12 sec. ON
6 sec. ON
8 sec. OFF
14 sec. OFF
20 sec. OFF
28 sec. OFF
HIGH
MEDIUM
HIGH
MEDIUM
MEDIUM 
LOW
LOW
Approx. 70%
Approx. 50%
Approx. 30%
Approx. 10%
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
When the microwave oven is preset for variable cooking
power,the 220- 230volts A.C. poweris suppliedto thehigh
voltage transformer intermittently within a 32-second time
base through the relay contact which is coupled with the
current-limitingrelayRY2.Thefollowinglevelsofmicrowave
power are given.

5
R-7A55(W)/(B)
R-7E45(W)/(B)
2. The coil of shut-off relay RY3 is energized by the control
unitandthemainsupplyvoltageisaddedtotheconvection
heating element.
3. Whentheoventemperaturereachestheselectedpreheat
temperature, the following operations occur;
3-1. The shut-off relay RY3 is de-energized by the control
unit temperature circuit and thermistor, opening the
circuit to the convection heating element.
3-2. The oven will continue to function for 15 minutes,
turning the convection heating elements on and off, as
needed to maintain the selected preheat temperature.
The oven will shut-down completely after 15 minutes.
CONVECTION COOKING CONDITION (Figure O-3)
Whenthepreheattemperatureisreached,abeepsignal will
sound indicating that the holding temperature has been
reachedintheovencavity.Openthedoorandplacethefood
tobecookedintheoven. Programdesired cookingtimeand
convectiontemperaturebytouchingtheCONVECTIONkey.
When the START key is touched, the following operations
occur:
1. The numbers of the digital readout start the count down
to zero.
2. The oven lamp, cooling fan motor, turntable motor and
convection motor are energized.
3. RelayRY3isenergizedIfthecavitytemperatureislower
than the selected temperature) and the main supply
voltage is applied to the convection heating element to
return to the selected cooking temperature.
4. Upon completion of the cooking time, the audible signal
will sound, and oven lamp, turntable motor, cooling fan
motorandconvectionmotorarede-energized.Attheend
ofconvectioncycle, if thecavityairtemperatureis above
104˚C, the circuit to RY6 will be maintained (by the
thermistorcircuit)tocontinueoperationofthecoolingfan
motor until temperature drops below 104˚C, at that time
the relay will be de-energized, turning off the fan motor .
GRILL COOKING CONDITION (Figure O-4)
In this condition the food is cooked by grill heating element
energy. And at the initial period (approximately 10 minutes)
the convection heater element is also activated. Program
desired cooking time and grill mode by touching TIME keys
and GRILL key. When the START key is touched, the
following operations occur:
1. The numbers of the digital readout start the count down
to zero.
2. The oven lamp, cooling fan motor, turntable motor and
convection motor are energized.
3. The relay RY5 is energized and the grill heating element
is energized.
4. The relay RY3 is energized, if the cavity temperature is
lower than 210˚C. When the cavity temperature reaches
210˚C, relay RY4 and RY3 are de-energized.
5. Now, the food is grilled by the grill heating elements..
DUAL COOKING CONDITION
MICROWAVE AND CONVECTION (Figure O-5)
Program desired cooking time and Dual cook mode by
touching the TIME keys and DUAL COOK key once. When
the START key is touched, the following operations occur:
1. The numbers of the digital readout start the count down
to zero.
2. The oven lamp, cooling fan motor, turntable motor and
convection motor are energized.
3. RelayRY3isenergized(Ifthecavitytemperatureislower
than the selected temperature) and the main supply
voltage is applied to the convection heating element.
4. Relay RY2 is energized and the microwave energy is
generated by magnetron.
5. Now,thefoodiscookedbythemicrowaveandconvection
heating elements energy simultaneously.
DUAL COOKING CONDITION
MICROWAVE AND GRILL (Figure O-6)
Program desired cooking time and Dual cook mode by
touching the TIME keys and DUAL COOK key twice. When
the START key is touched, the following operations occur:
1. The numbers of the digital readout start the count down
to zero.
2. The oven lamp, cooling fan motor, turntable motor and
convection motor are energized.
3. Relay RY5 is energized and the main supply voltage is
applied to the grill heating element.
4. Relay RY2 is energized and the microwave energy is
generated by magnetron.
5. Now, the food is cooked by the microwave and grill
heating elements energy simultaneously.
POTATO, INSTANT ACTION
When the menu and quantity are input, the oven chooses
cooking mode (Microwave, Convection, Grill or Dual) and
sets cooking time automatically according to the pre-pro-
grammed information in IC-1 (LSI).

6
R-7A55(W)/(B)
R-7E45(W)/(B)
FUNCTION OF IMPORTANT COMPONENTS
DOOR OPEN MECHANISM
The door can be opened by pushing the open button on the
control panel. When the open button is pushed, the open
lever pushes lower latch head on the door upward. The
upperlatch headis linked withthe lowerlatchhead, sonow,
the door can be opened. FUSE F1 15A 250V
If the wire harness or electrical components are short-
circuited,this fuse F115A 250Vblows to preventan electric
shock or fire hazard.
FUSE F2 F6.3A 250V
1. If the wire harness or electrical components are short-
circuited, this fuse blows to prevent an electric shock or
fire hazard.
2. The fuse also blows when 1st latch switchSW1remains
closed with the oven door open and when the monitor
switch SW4 contact (COM-NC) closes.
FUSE F3 F10A 250V
1. If the wire harness or electrical components are short-
circuited, this fuse blows to prevent an electric shock or
fire hazard.
2. The fuse also blows when the asymmetric rectifier, H.V.
rectifier,.H.V.wireharness,H.V.capacitor,magnetronor
secondarywindingofhighvoltagetransformerisshorted.
MONITOR RESISTOR R1
The monitor resistor prevents the fuse F2 F6.3A 250V
bursting when the fuse F2 F6.3A 250V blows due to the
operation of the monitor switch circuit.
Figure D-1. Door Open Mechanism
1ST LATCH SWITCH SW1, 2ND LATCH
SWITCH SW2 AND STOP SWITCH SW3
1. When the oven door is closed, the contactsCOM-NO of
each switch must be closed.
2. Whentheovendoorisopened,thecontactsCOM-NOof
each switch must be opened.
MONITOR SWITCH SW4
Themonitorswitchisactivated(thecontactsopened)bythe
lower latch head on the door while the door is closed. The
switch is intended to render the oven inoperative by means
of blowing the fuse F2 (F6.3A) when the contacts of the 1st
latch switch SW1 fail to open when the door is opened.
Function
1. When the door is opened, the contacts (COM-NC) of
monitor switch SW4 close (to the ON condition) due to
their being normally closed and contacts (COM-NO)
open. At this time the 1st latch SW1 is in the OFF
condition (contacts open) due to their being normally
open contact switches.
2. Asthe doorgoes toa closedposition, themonitor switch
SW3contacts(COM-NC)areopenedandcontacts(COM-
NO)closedand2ndlatchswitchSW2 contactsCOM-NO
are closed and then the 1st latch switch and stop switch
contacts close.(On opening the door, each of these
switches operate inversely.)
3. If the door is opened and the 1st latch switch SW1
contacts fail to open, the fuse F2 (F6.3A) blows
immediately after closing of the monitor switch (COM-
NC) contacts.
CAUTION: BEFORE REPLACING A BLOWN FUSE F2
F6.3ATESTTHE1STLATCH SWITCH,MONI-
TORSWITCHANDMONITORRESISTORFOR
PROPER OPERATION.
(REFERTOCHAPTER“TESTPROCEDURE”).
TC TRANSFORMER
TCtransformerconvertsA.C.linevoltageintolowvoltageto
drive the control unit.
THERMAL CUT-OUT TC1 170˚C (OVEN)
The thermal cut out protects the oven against overheat
during grill cooking, convection cooking or dual (combina-
tion)cooking.Ifthetemperaturerisesabove170˚Cbecause
thefanmotorisinterrupted,theairinletductisblockedorthe
ventilation openings are obstructed, the thermal cut-out
opens and switches off the all electrical parts.
The defective thermal cut-out must be replaced with a new
one.
THERMAL CUT-OUT TC2 125˚C (MG)
This thermal cut-out protects the magnetron against over-
heat.Ifthetemperature goesuphigherthan125˚Cbecause
the fan motor is interrupted or the ventilation openings are
blocked, the thermal cut-out TC2 will open and line voltage
tothe highvoltage transformer T willcut offand operationof
the magnetron MG will be stopped. The defective thermal
cut-out must be replaced with a new one.
THERMAL CUT-OUT TC3 190˚C (CONV.)
The thermal cut out protects the convection motor CM
against overheat. If the temperature of the thermal cut-out
TC3 rises above 190˚C because the convection fan is
interrupted, the ventilation openings are obstructed or the
otherabnormalmatteroccurs,thethermalcut-outopensand
switches off the convection heating element and conv.
indicator light. When the oven cools itself down to the
operating temperature of 170˚C, the contacts of the thermal
cut-out will close again.
LATCH
HEADS
LATCH HOOK
STOP
SWITCH
MONITOR
SWITCH
1ST. LATCH 
SWITCH
OPEN LEVER
DOOR OPEN BUTTON
2ND. LATCH
SWITCH

7
R-7A55(W)/(B)
R-7E45(W)/(B)
ASYMMETRIC RECTIFIER
The asymmetric rectifier is solid state device that prevents
current flow is both directions. And it prevents the tempera-
ture rise of the power transformer by blowing the fuse F3
F10A when the high voltage rectifier is shorted.
AB
C
D2 D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE RECTIFIER
The rated peak reverse voltage of D1 of the asymmetric
rectifier is 6 KV The rated peak reverse voltage of D2 of the
asymmetric rectifier is 1.7 KV. D1 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 the blowing the fuse F3
F10A.)
1. The high voltage rectifier is shorted by any causes when
microwave cooking or dual cooking.
2. The peak reverse voltage of D2 of the rectifier goes
beyond the rated peak reverse voltage 1.7 KV in the
voltage doubler circuit.
3. D2 of the rectifier is shorted.
4. The large electric currents flow through the high voltage
winding of the high voltage transformer.
5. The large electric currents beyond 10A flow through the
primary winding of the high voltage transformer.
6. The fuse F3 F10A blows by the large electric currents.
7. The power supplying to the high voltage transformer is
cut off.
TURNTABLE MOTOR TTM
The turntable motor drives the roller stay to rotate the
turntable.
FAN MOTOR FM
The fan motor drives a blade which draws external cool air.
Thiscoolairisdirectedthroughtheairvanessurroundingthe
magnetron and cools the magnetron. This air is channeled
throughthe ovencavitytoremove steamandvapours given
off from the heating foods. It is then exhausted through the
exhausting air vents at the oven cavity.
CONVECTION MOTOR CM
Theconvectionmotor drivestheconvectionfan andprovide
the heated air.
NOISE FILTER
The noise filter assembly prevents radio frequency interfer-
ence that might flow back in the power circuit.
GRILL HEATING ELEMENT GH
The grill heating element is provided to brown the food and
is located on the top of the oven cavity.
CONVECTION HEATING ELEMENT CH
The convection heating element is located at the rear of the
ovencavity.Itisintendedtoheatairdrivenbytheconvection
fan. The heated air is kept in the oven and force-circulated
and reheated by the convection heating element.
CONVECTION COOKING SYSTEM
This oven is designed with a hot air heating system where
food is not directly heated up by the convection heating
element,butisinsteadheatedbyforcedcirculationofthehot
air produced by the convection heating element.
The air heated by the convection heating element is circu-
lated through the convection passage provided on the outer
casing of the oven cavity by means of the convection fan
which is driven by the convection motor. It then enters the
inside of the oven through the vent holes provided on the
backside ofthe oven.Next, thehot air heatsthe foodon the
turntable and leaves the oven cavity through the vent in the
oven cavity rear wall.
Without leaving the oven, this hot air is reheated by the
convectionheatingelement, passesthroughtheconvection
passage and enters the inside of the oven cavity again, in a
continuing cycle.
In this way, the hot air circulates inside the oven cavity to
raise its temperature and, at the same time, comes into
contact with the food being cooked.
When the temperature inside the oven cavity reaches the
selectedtemperature,theconvectionheatingelementisde-
energized. When the temperature inside the oven cavity
drops below the selected temperature, the convection heat-
ing element is energized again. In this way, the inside of the
oven cavity is maintained at approximately the selected
temperature.
Whenthe convectiontime reaches “0”,the convectionheat-
ing element is de-energized and the convection fan stops
operating and the oven shuts off. At the high temperature
(morethan104˚C),thefanmotorremainsrotating.Automati-
callythefanmotorwillbeshutdownatlowtemperature(less
than 104˚C).
Door Oven Cavity Grill Heating
Elements Convection
Passage
Convection
Heating
Element
Auxiliary
Fan
Convection
Motor
Convection
Fan
Turntable
Roller Stay
Turntable
Motor
Figure D-2. Convection Cooking System

8
R-7A55(W)/(B)
R-7E45(W)/(B)
DAMPER OPEN-CLOSE MECHANISM
Usually, the damper is in the open position except during
convection cooking, grill cooking and dual cooking.
Damper position is set automatically by damper motor,
damper switch, damper cam and damper shaft.
These components are operated by a signal that judges if
microwavecookingorothercookingoperationisselectedby
the CPU unit.
Microwave Cooking:
Damperis intheopen position,becausea portionofcooling
air is channeled through the cavity to remove steam and
vapors given off from the heating foods.
It is then exhausted at the top of the oven cavity into a
condensation compartment.
Convection, Grill and Dual Cooking:
Damper is in the closed position, so that no hot air will be
allowed to leak out the oven cavity.
Damper Operation
1. When power supply cord is plugged in:
1-1. When power supply cord is plugged in, a signal is
sensed in the control unit, and operates shut-off relay
(RY7).
1-2. Contacts of shut-off relay (RY7) close, the damper
motor is energized, opening the damper door.
1-3. When the damper is moved to the open position by the
damper cam, damper switch is closed (ON position).
1-4. The signal of damper switch is re-sensed in the control
unit and shut-off relay (RY7) is turned off.
1-5. The A.C. line voltage A.C. to the damper motor is
stopped and the motor turns off.
2. When oven is microwave cooking:
Damper is in the open position
3. When oven is convection, grill or dual cooking:
3-1 Damper motor is energized right after the oven is
started.
3-2. When damper is in the closed position (damper switch
isOFF),itssignalissensedbythecontrolunit,andshut-
off relay (RY7) is de-energized.
3-3. The damper is held in the closed position during the
cooking operation
3-4. At the end of the cooking, shut-off relay (RY7) is
energized, and the damper is returned to the open
position.
NOTE: If the damper door is not in the proper position,
closed durining convection, grill or dual, or open
durning microwave, the control unit will stop oven
operation after 1 minute.
Cooking Mode Operation of Damper
Microwave cooking OPEN
Convection cooking CLOSE
Grill cooking CLOSE
Dual cooking CLOSE
SENSING FIRE OPERATION
The oven will stop its operation when there is a fire in the
oven cavity in microwave cooking condition.
LSImeasuresthevoltage acrossthetemperaturemeasure-
mentcircuitintermittentlywithina32-secondtimebaseafter
since the oven is started in microwave cooking condition.
The oven will stop its operation when the difference of the
voltages is more than 0.3 volts in microwave cooking condi-
tion.
1. Withina32-secondbase,firstthethermistorisenergized
for 3 seconds. After 2 seconds since the thermistor is
energized, the voltage across the temperature
measurement circuit is measured. And after 21 seconds
since the thermistor is cut off, the convection motor
operates for 10 seconds.
2. The oven carries out the procedure above again. If the
second voltage is 0.3V higher than the first voltage, LSI
judges it is a fire in the oven cavity and stops the oven.
3. When sensor cooking, the sensing fire operation is not
carried out until the oven senses the steam from food.
Because food cannot be cooked well by rotating the
convection fan at that time. After sensing the steam, the
sensing fire operation is started.
4. WhenLSIjudgesitisfireintheovencavity,LSIwillswitch
off the relays to the power transformer, fan motor and
convectionmotorandLSIstopscountingdown.Andthen
the damper is closed so that the fresh air does not come
into the oven cavity.
CONVECTION
MOTOR
THERMISTOR
Sensing
Voltage
ON
OFF
ON
OFF
ON
OFF
0 2 20 30 32 64 (sec.)
3 sec.
Sensing the voltage across temperature measurement circuit.
10 sec.

9
R-7A55(W)/(B)
R-7E45(W)/(B)
TROUBLESHOOTING GUIDE
Whentroubleshooting themicrowaveoven,it ishelpfulto followtheSequence of Operationinperforming thechecks.Many
ofthepossiblecausesoftroublewill require thata specifictest beperformed. Thesetests aregiven aprocedure letterwhich
will be found in the “Test Procedure” section.
IMPORTANT: Ifthe ovenbecomes inoperativebecauseof ablown fuseF2(F6.3A) inthe1st latchswitch -monitorswitch
- monitor resistor circuit, check the 1st latch switch, monitor switch and monitor resistor before replacing
the fuse F2 (F6.3A).
SERVICING
WARNING TO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of producing very high voltage and current. Contact with following parts
will result in electrocution.
Highvoltage capacitor,Highvoltage transformer,Magnetron,High voltage rectifierassembly,High voltageharness.
REMEMBER TO CHECK 4R
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.
Microwave ovens should not be run empty. To test for
thepresenceofmicrowaveenergywithinacavity,place
acupofcoldwaterontheoventurntable,close thedoor
andsetthemicrowavetimerfortwo(2)minutes.Andset
the power level to HIGH (100%) and push the start key.
When the two minutes has elapsed (timer at zero)
carefully check that the water is now hot. If the water
remains cold carry out 3D checks and re-examine the
connections to the component being tested.
REMEMBER TO CHECK 3D
1) Disconnect the supply.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.
WARNING AGAINST THE CHARGE OF THE
HIGH-VOLTAGE CAPACITOR
The high-voltage capacitor remains charged
about 60 seconds after the oven has been
switchedoff.Waitfor60secondsandthenshort-
circuittheconnectionofthehigh-voltagecapacitor
(thatis,oftheconnectingleadofthehigh-voltage
rectifier) against the chassis with the use of an
insulated screwdriver.
Sharp recommend that wherever possible fault-finding
is carried out with the supply disconnected. It may in,
some cases, be necessary to connect the supply after
theoutercasehasbeenremoved,inthiseventcarryout
3Dchecksandthendisconnect theleadstotheprimary
ofthehighvoltagetransformer.Ensurethattheseleads
remain isolated from other components and the oven
chassis. (Use insulation tape if necessary.) When the
testingiscompletedcarryout3Dchecksandreconnect
theleads totheprimary ofthehigh voltage transformer.
Whenallserviceworkiscompleted,andtheovenisfullyassembled,themicrowavepoweroutputshouldbechecked
and microwave leakage test carried out.

10
R-7A55(W)/(B)
R-7E45(W)/(B)
PROBLEM
Fuse F2 F6.3A browns when the door is opened.
Home fuse blows when power cord is plugged into wall outlet.
FuseF1 15Abrowns when powercord isplugged intowall outlet.
"88:88" does not appear in display when power cord is plugged
into wall outlet.
Display does not operate properly when STOP/CLEAR key is
touched.
Oven lamp does not light when door is opened. (Display oper-
ates.)
Oven does not start when the START key is touched. (Display
operates.)
Oven lamp does not light And turntable motor does not operate.
Fan motor does not operate. (Oven lamp lights.)
Convection fan motor does not operate. (Oven lamp lights.)
Turntable motor does not operate. (Oven lamp lights.)
Ovenoranyelectricalparts(exceptfanmotor)doesnotstopwhen
cooking time is 0 or STOP/CLEAR key is touched.
Oven stops after about 4 minutes since START key is touched.
(Except Microwave and Dual Cook modes)
Display operates properly but all electrical parts do not operate.
The oven stops 1 minute after starting.
Oven goes into cook cycle but shuts down before end of cooking
cycle.
Aftercooking,thetemperatureofovencavityishigherthan104˚C
but the fan motor does not operate.
Oven seems to be operating but little or no heat is produced in
oven load. (Microwave power control is set at HIGH)
Oven does not seem to be operating properly during variable
cooking condition. (Oven operates properly at HIGH)
Oven goes into cook cycle but shuts down before end of cooking
cycle.
Convection heating element does not heat.
Oven seems to be operate when the temperature in the oven
cavity is lower or higher than preset one.
Grill heating element does not heat.
Convectionheating elementdoesnot stopwhenthe temperature
of oven cavity is higher than 210˚C or it stop to heat when the
temperature of oven cavity is lower than 210˚C
Oven goes into cook cycle but shuts down before end of cooking
cycle.
Oven seems to be operating but little or no heat is produced in
oven load. (Microwave power does not seem to be generated
properly)
Ovenseemsto beoperatingbut thetemperatureofovencavityis
lower or higher than preset one.
Convection heating element does not heat.
Grill heating element does not heat.
TEST PROCEDURE
OFF
CONDITION
DUAL COOKING
CONDITION
(MICRO./GRILL)
MAGNETRON HIGH VOLTAGE TRANSFORMER H.V. RECTIFIER ASSEMBLY H.V. HARNESS HIGH VOLTAGE CAPACITOR 1ST. LATCH SWITCH 2ND. LATCH SWITCH STOP SWITCH MONITOR SWITCH MONITOR RESISTOR DAMPER SWITCH THERMAL CUT-OUT 170˚C TC1 THERMAL CUT-OUT 125˚C TC2 THERMAL CUT-OUT 190˚C TC3 TURNTABLE MOTOR
ABC DEEEEFEGGGH
COOKING
CONDITION
(
COMMON MODE)
MICROWAVE
COOKING
CONDITION
CONVECTION
COOKING
CONDITION
DUAL COOKING
CONDITION
(COMMON MODE)
DUAL COOKING
CONDITION
(MICRO./CONV.)
GRILL
COOKING
CONDITION
POSSIBLE CAUSE
AND
DEFECTIVE PARTS

11
R-7A55(W)/(B)
R-7E45(W)/(B)
HHHL I K JMMN O PQ
FAN MOTOR DAMPER MOTOR CONVECTION FAN MOTOR FUSE F3 F10A NOISE FILTER FUSE F2 F6.3A FUSE F1 15A GRILL HEATING ELEMENT CONVECTION HEATING ELEMENT THERMISTOR POWER SUPPLY CORD SHORTED WIRE HARNESS OPENED WIRE HARNESS OVEN LAMP OR SOCKET TC TRANSFORMER TOUCH CONTROL PANEL
BLOCKED VENTILATION OPENINGS WRONG OPERATION MIS-ADJUSTMENT OF SWITCHES HOME FUSE OR BREAKER NO POWER AT WALL OUTLET BLOCKED CONVECTION FAN BLOCKED COOLING FAN RELAY (RY1, 2, 3, 4, 5, 7) FOIL PATTERN

12
R-7A55(W)/(B)
R-7E45(W)/(B)
COMPONENT TEST
CARRY OUT 3D CHECK
Isolate the magnetron from high voltage circuit by removing all leads connected to 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 short 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 infinite resistance. If a low or
zero resistance reading is obtained then the magnetron should be replaced.
MICROWAVE OUTPUT POWER (IEC-705-1988)
The following test procedure should be carried out with the microwave oven in a fully assembled
condition (outer case fitted). Microwave output power from the magnetron can be measured by way of
IEC 705, i.e. it can be measured by using water load how much it can be absorbed by the water load.
Tomeasurethemicrowaveoutputpowerin the microwaveoven, therelation ofcalorie andwatt isused.
When P(W) heating works for t(second), approximately P x t/4.187 calorie is generated. On the other
hand, if the temperature of the water with V(ml) rises∆T (°C) during this microwave heating period, the
calorie of the water is V x ∆T.
The formula is as follows;
P x t / 4.187 = V x ∆T P (W) = 4.187 x V x ∆T / t
Our condition for water load is as follows:
Room temperature..............around 20°C Power supply Voltage.........Rated voltage
Water load.........1000 g Initial temperature...........10±2°C Heating time.........42 sec.
P=100x∆T
NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL
WHILE THE OVEN IS IN OPERATION.
TEST PROCEDURES
PROCEDURE
LETTER
AMAGNETRON TEST
Measuring condition:
1. Container
The water container must be a cylindrical borosilicate glass vessel having a maximum material
thickness of 3 mm and an outside diameter of approximately 190 mm.
2. Temperature of the oven and vessel
The oven and the empty vessel are at ambient temperature prior to the start the test.
3. Temperature of the water
The initial temperature of the water is (10±2)°C.
4. Selecttheinitialand finalwatertemperaturesothatthe maximumdifferencebetweenthefinalwater
temperature and the ambient temperature is 5K.
5. Select stirring devices and measuring instruments in order to minimize addition or removal of heat.
6. Thegraduationofthethermometermustbescaledby0.1°Catminimumandaccuratethermometer.
7. The water load must be (1000±5) g.
8. “t” is measured while the microwave generator is operating at full power. Magnetron filament heat-
up time is not included.
NOTE:Theoperationtimeofthemicrowaveovenis“t+2”sec.2sec.ismagnetronfilamentheat-uptime.
Measuring method:
1. Measure the initial temperature of the water before the water is added to the vessel.
(Example: The initial temperature T1 = 11°C)
2. Add the 1 litre water to the vessel.
3. Place the load on the centre of the shelf.
4. Operate the microwave oven at HIGH for the temperature of the water rises by a value ∆T of
(10 ±2) K.
5. Stir the water to equalize temperature throughout the vessel.

13
R-7A55(W)/(B)
R-7E45(W)/(B)
PROCEDURE
LETTER COMPONENT TEST
6. Measure the final water temperature. (Example: The final temperature T2 = 21°C)
7. Calculate the microwave power output P in watts from above formula.
Initial temperature ......................................................................................................... T1 = 11°C
Temperature after (42 + 2) = 44 sec. ............................................................................ T2 = 21°C
Temperature difference Cold-Warm............................................................................ ∆T1 = 10°C
Measured output power
The equation is “P = 100 x ∆T” ........................................................P = 100 x 10°C = 1000 Watts
TEST PROCEDURES (CONT'D)
JUDGMENT: The measured output power should be at least ±15 % of the rated output power.
CAUTION: 1°C CORRESPONDS TO 100 WATTS. REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
AB
C
D2 D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE RECTIFIER
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 infinite in one direction and more than 100 kΩin the other direction.
CARRY OUT 4R CHECKS
ASYMMETRIC RECTIFIER TEST
CARRY OUT 3D CHECKS.
CARRY OUT 3D CHECKS
Disconnecttheleadstotheprimarywindingofthehighvoltagetransformer.Disconnectthefilamentand
secondarywindingconnectionsfromtherestoftheHVcircuitry.Usinganohmmeter,setonalowrange,
it is possible to check the continuity of all three windings. The following readings should be obtained:-
If the reading obtained are not stated above, then the high voltage transformer is probably faulty and
should be replaced.
CARRY OUT 4R CHECKS
a. Primary winding 1.22 ohms approximately
b. Secondary winding 81.7 ohms approximately
c. Filament winding less than 1 ohm
WARNING: High voltages and large currents are present at the secondary winding and
filamentwindingtransformer.Itisverydangeroustoworknearthispartwhen
the oven is on. NEVER make any voltage measurements of the high-voltage
circuits, including the magnetron filament.
BHIGH VOLTAGE TRANSFORMER TEST
1000g
1000g
1000g
T1˚C T2˚C
Heat up for 44 sec.

14
R-7A55(W)/(B)
R-7E45(W)/(B)
Table: Resistance
Resistor Resistance
Monitor resistor Approx. 4.3Ω
PROCEDURE
LETTER COMPONENT TEST
TEST PROCEDURES (CONT'D)
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric can be tested using an
ohmmeter set to its highest range 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 direction then the asymmetric rectifier is good. If an asymmetric rectifier is shorted in either
direction,thentheasymmetricrectifierisprobablyfaultyandmustbereplacedwithhighvoltagerectifier.
Whentheasymmetricrectifierisdefective,checkwhethermagnetron,highvoltagerectifier,highvoltage
wire or filament winding of the power transformer is shorted.
CARRY OUT 4R CHECKS
NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF
THEMEASURINGINSTRUMENTMUSTHAVEAVOLTAGEATLEAST6VOLTS,BECAUSE
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.
D HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS
A. Isolate the high voltage capacitor from the circuit.
B. Continuitycheckmustbecarriedoutwithmeasuringinstrumentwhichissettothehighestresistance
range.
C. Anormalcapacitorshowscontinuityforashorttime(kick) andthenaresistanceofabout10MΩafter
it has been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 MΩbecause of its internal 10MΩ
resistance.
F. When the internal wire is opened in the high voltage capacitor shows an infinite resistance.
G. Theresistanceacrossalltheterminalsandthechassismustbeinfinitewhenthecapacitoris normal.
If incorrect reading are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS
ESWITCH TEST
CARRY OUT 3D CHECKS
Isolatetheswitch to betestedandusingan ohmmetercheckbetweentheterminals asdescribedinthe
following table.
COM; Common terminal, NO; Normally open terminal NC; Normally close terminal
S.C.; Short, O.C.; Open circuit
Table: Terminal Connection of Switch
Plunger Operation COM to NO COM to NC
Released O.C. S.C.
Depressed S.C. O.C.
If incorrect readings are obtained, make the necessary switch or replace the switch.
CARRY OUT 4R CHECKS.
FMONITOR 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.
If incorrect readings are obtained, replace the monitor resistor.
CARRY OUT 4R CHECKS

15
R-7A55(W)/(B)
R-7E45(W)/(B)
COMPONENT TEST
TEST PROCEDURES (CONT'D)
GTHERMAL CUT-OUT TEST
PROCEDURE
LETTER
CARRY OUT 3D CHECKS
Disconnect the leads from the terminals of the thermal cut-out. Then using an ohmmeter, make a
continuity test across the two terminals as described in the below.
CARRY OUT 4R CHECKS
If incorrect readings are obtained, replace the thermal cut-out.
Anopencircuitthermalcut-out(MG) TC1indicatesthatthemagnetronhasoverheated,thismaybedue
to resistricted ventilation, cooling fan failure.
An open circuit thermal cut-out (OVEN)TC2 indicates that the oven cavity has overheated, this may be
due to no load operation.
An open circuit thermal cut-out (CONV.) TC3 indicates that the convection fan motor winding has
overheated,thismaybeduetoresistedventilationorlockedcoolingfanorlockedconvection fan motor.
Table: Thermal Cut-out Test
Temperature of Temperature of Indication of
"ON" condition "OFF" condition ohmmeter
Parts Name (closed circuit). (open circuit). (When room
(˚C) (˚C) temperature is
approx. 20˚C.)
Thermal cut-out This is not resetable Above 170˚C Closed circuit
170˚C TC1 type.
Thermal cut-out This is not resetable Above 125˚C Closed circuit
125˚C TC2 type
Thermal cut-out Below 170˚C Above 190˚C Closed circuit.
190˚C TC3
H MOTOR WINDING TEST
CARRY OUT 3D CHECKS
Disconnect the leads from the motor. Using an ohmmeter, check
theresistancebetweenthetwoterminalsas described inthe table
below.
INOISE FILTER TEST
CARRY OUT 3D CHECKS
Disconnect the leads from the terminals of
noise filter.
Using an ohmmeter, check between the ter-
minals as described in the following table.
L
NL
L
15A Cx
Cy RED
WHT
F6.3A
R1
R2
If incorrect readings are absorbed, replace the noise filter unit.
CARRY OUT 4R CHECKS
MEASURING POINTS INDICATION OF OHMMETER
Between N and L Approx. 680 kΩ
Between terminal N and WHITE Short circuit
Between terminal L and RED Short circuit
L (min) Cx ±20% Cy ±20%
1.0mH 0.22µF 4700pF
R1: 10 MΩ±20%
R2 : 680 kΩ±20%
If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS
Table: Resistance of Motor
Motors Resistance
Fan motor Approximately 182 Ω
Turntable motor Approximately 16 kΩ
Convection fan motor Approximately 163 Ω
Damper motor Approximately 16 kΩ

16
R-7A55(W)/(B)
R-7E45(W)/(B)
COMPONENT TEST
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER
JFUSE F1 15A
CARRY OUT 3D CHECKS
If the fuse F115A is blown, there is a shorts or grounds in electrical parts or wire harness. Check them
and replace the defective parts or repair the wire harness.
CARRY OUT 4R CHECKS
CAUTION: Only replace fuse with the correct value replacement.
K BLOWN FUSE F2 F6.3A
CARRY OUT 3D CHECKS
1. IfthefuseF2F6.3Aisblownwhenthedoorisopened,checkthe1stlatchswitch,monitorswitchand
monitor resistor.
2. IfthefuseF2F6.3Aisblownbyincorrectdoorswitchingreplacethedefectiveswitch(es)andthefuse
F2 F6.3A.
3. If the fuseF2 F6.3A is blown, there could be a shorts or grounds in electrical parts or wire harness.
Check them and replace the defective parts or repair the wire harness.
CARRY OUT 4R CHECKS
CAUTION: Only replace fuse F2 F6.3A with the correct value replacement.
LBLOWN FUSE F3 F10A
CARRY OUT 3D CHECKS
1. If the fuse F3 F10A is blown, there could be shorts or grounds in electrical parts or wire harness.
Check them and replace the defective parts or repair the wire harness.
2. If the fuse F3 F10A is blown, there could be shorts in the asymmetric rectifier or there is a ground
in wire harness. A short in the asymmetric rectifier may be occurred due to short or ground in H.V.
rectifier, magnetron, high voltage transformer or H.V. wire. Check them and replace the defective
parts or repair the wire harness.
CARRY OUT 4R CHECKS
CAUTION: Only replace fuse F3 F10A with the correct value replacement.
M CONVECTION HEATING ELEMENT AND GRILL HEATING ELEMENT TEST
CARRY OUT 3D CHECKS
Before carrying out the following tests make sure the heating element is cool completely.
1. Resistance of heating element.
Disconnect the wire leads to the heating element to be tested. Using ohmmeter with low resistance
range.Checktheresistanceacrosstheterminalsoftheheatingelementasdescribedinthefollowing
table.
Table: Resistance of heating element
Parts name Resistance
Convection heating element Approximately 39 Ω
Grill heating element Approximately 22 Ωx 2 = 44 Ω
2. Insulation resistance.
Disconnect the wire leads to the heating element to be tested. Check the insulation resistance
between the element terminal and cavity using a 500V - 100MΩinsulation tester. The insulation
resistance should be more than 10M&ohm in the cold start.
If the results of above test 1 and/or 2 are out of above specifications, the heating element is probably
faulty and should be replaced.
CARRY OUT 4R CHECKS

17
R-7A55(W)/(B)
R-7E45(W)/(B)
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER COMPONENT TEST
CARRY OUT 3D CHECKS.
DisconnectconnectorBfromCPUunit.Measuretheresistanceofthermistorwithanohmmeter.Connect
the ohmmeter leads to Pin No's B5 and B6 of the thermistor harness.
Room Temperature Resistance
20˚C - 30˚C Approximately 326 kΩ- 175 kΩ
If the merter does not indicate above resistance, replace the thermistor.
CARRY OUT 4R CHECKS.
N THERMOSTAT TEST
KTOUCH CONTROL PANEL ASSEMBLY TEST
The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc.
Therefore, unlike conventional microwave ovens, proper maintenance cannot be performed with
only a voltmeter and ohmmeter.
In this service manual, the touch control panel assembly is divided into two units, Control Unit
and Key Unit, and troubleshooting by replacement is described according to the symptoms
indicated.
1. Key Unit. Note: Check key unit ribbon connection before replacement.
The following symptoms indicate a defective key unit. Replace the key unit.
a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.
2. Control Panel
The following symptoms indicate a defective control unit. Before replacing the control unit,
perform the Key unit test (Procedure L) to determine if control unit is faulty.
2-1 In connection with pads.
a) When touching the pads, a certain group of pads do not produce a signal.
b) When touching the pads, no pads produce a signal.
2-2 In connection with indicators
a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 Other possible problems caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.
L KEY UNIT TEST
If the display fails to clearwhen the STOP pad is depressed, first verify the flat ribbon is
marking good contact, verify that the door sensing switch(stop switch) operates properly; that
is the contacts are closed when the door is closed andopen when the door is open. If the door
sensing switch(stop switch) is good, disconnecct the flat ribbon cable that connects the key
unit to the control unit and make sure the door sensing switch is closed (either close the door
or short the door sensing switch connecter). Use the Key unit matrix indicated on the control
panel schematic and place a jamper wire between the pins that correspond to the STOP pad
marking momentary contact. If the control unit responds by clearing with a beep the key unit is
faulty and must be replaced. If the control unit does not respond, it is a faulty and must be
replaced. If a specific pad does not respond, the above method may be used (after clearing
the control unit) to determine if the control unit or key pad is at fault.

18
R-7A55(W)/(B)
R-7E45(W)/(B)
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER COMPONENT TEST
KEY UNIT
G-1
G-2
G-3G-4G-5G-6G-7
G-8
G-9
G-10
G-11
G-12
STOP 10
S
1
MIN

10
MIN
R-7A55(B)/(W)
KEY UNIT
G-1
G-2
G-3G-4G-5G-6G-7
G-8
G-9
G-10
G-11
G-12
STOP 10
S
1
MIN

10
MIN
R-7E45(B)/(W)
CARRY OUT 4R CHECKS
MRELAY TEST
CARRY OUT 3D CHECKS
Remove the outer case and check voltage between Pin Nos. 1 and 3 of the 9 pin connector (A)
on the control unit with an A.C. voltmeter.
The meter should indicat 220~230 volts, if not check oven circuit.
Relay Test
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation,
convection cooking operation or grill 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.
RELAY SYMBOL OPERATIONAL
VOLTAGE CONNECTED COMPONENTS
RY1 Approx. 20.0V.D.C. Oven lamp/Turntable motor
RY2 Approx. 18.5V.D.C. High voltage transformer
RY3 Approx. 20.0V.D.C. Convection heating element
RY4 Approx. 26.0V.D.C. Convection motor
RY5 Approx. 20.0V.D.C. Grill heating element
RY6 Approx. 26.0V.D.C. Fan motor
RY7 Approx. 26.0V.D.C. Damper motor
CARRY OUT 4R CHECKS