Sharp R-8740 (serv.man17) Service Manual ▷ View online
R-8740M - 33
After any repair, the microwave oven must be checked for
microwave leakage to ensure continued safe operation
BS EN 60335-2-25 specifies that the maximum permitted
leakage with a load of 275ml is 50 W/m
microwave leakage to ensure continued safe operation
BS EN 60335-2-25 specifies that the maximum permitted
leakage with a load of 275ml is 50 W/m
2
(equivalent to
5mW/cm
2
) at a distance of 5cm from the oven.
PREPARATION
The following items are required to carry out this test:-
1.
1.
A low form of 600ml beaker made from
electrically non-conductive material, such as
glass or plastic, with an inside diameter of
approximately 8.5cm. This must contain 275 ±
15ml of water, at an initial temperature of 20 ±
2°C.
2.
glass or plastic, with an inside diameter of
approximately 8.5cm. This must contain 275 ±
15ml of water, at an initial temperature of 20 ±
2°C.
2.
A leakage detector which has been calibrated
within the preceding 12 months to a stand
whose accuracy can be traced to National
Physical Laboratory Standards.
whose accuracy can be traced to National
Physical Laboratory Standards.
Recommended instruments are:
Apollo "XI"
Celtec "A1000"
Celtec "A1000"
Before commencing the test, check the leakage detector is
functioning and adjusted according to the manufacturer's
instructions, and any spacers are fitted to ensure that
measurement is taken 5cm from the surface of the oven.
functioning and adjusted according to the manufacturer's
instructions, and any spacers are fitted to ensure that
measurement is taken 5cm from the surface of the oven.
Dotted line indicates the path taken by the leakage detector.
Whilst the maximum leakage permitted in BS EN 60335-2-25 is 50 W/m
2
(equivalent to 5mW/cm
2
), it is not
normal to detect anything significant, and therefore any detected leakage should be investigated.
PROCEDURE
1.
Place the beaker containing the water load
in the oven cavity at the centre of the
turntable. The placing of this standard load in
the oven is important, not only to protect the
oven, but also to ensure that any leakage it is
not disguised by too large a load absorbing
the energy.
in the oven cavity at the centre of the
turntable. The placing of this standard load in
the oven is important, not only to protect the
oven, but also to ensure that any leakage it is
not disguised by too large a load absorbing
the energy.
2.
Close the oven door, and with the power level
set to FULL, turn the oven ON with the timer
set for a few minutes operation. Should the
water begin to boil before the test has been
completed, it should be replaced.
set to FULL, turn the oven ON with the timer
set for a few minutes operation. Should the
water begin to boil before the test has been
completed, it should be replaced.
3.
As shown in the diagram below, move the
probe slowly (not faster than 2.5cm/sec);-
probe slowly (not faster than 2.5cm/sec);-
a)
around the edge of the door following the gap
b)
across the face of the door
c)
across any vents in the oven's sides, rear or
top
top
MICROWAVE MEASUREMENT
Microwave leakage measurement at 5 cm distance
SHARP
R-8740M - 34
TEST DATA AT A GLANCE
Parts
Symbol
Value / Data
Fuse
F1
20A 250V
Fuse
F2
F8A 250V
Thermal cut-out
TC1
150˚C
Thermal cut-out
TC2
125˚C
Thermistor
Approx. 326 kΩ - 175 kΩ at 20˚C - 30˚C
Top grill heating element
GH
Approx. 22 Ω. x 2 = 44 Ω
Insulation resistance > 10MΩ
Insulation resistance > 10MΩ
Bottom grill heating element
CH
Approx. 66Ω
Insulation resistance > 10MΩ
Insulation resistance > 10MΩ
Oven lamp
OL
240 - 250 V 25W E14
High voltage capacitor
C
1.07µF AC 2100V
Magnetron
MG
Filament < 1Ω
Filament - chassis ∞ ohm.
Filament - chassis ∞ ohm.
High voltage transformer
T
Filament winding < 1Ω.
Secondary winding Approx. 122Ω.
Primary winding Approx. 1.9Ω
Secondary winding Approx. 122Ω.
Primary winding Approx. 1.9Ω
Resistance (Disconnect the
In/Out put terminal
Test Point
Volt
power and door is closed)
Input terminal (Power supply)
A9 - A11
230V
Approx. 486 Ω
Input terminal (Stop switch)
B1 - B2
-
0
Input terminal (Thermistor)
C1 - C3
DC. 5V
Approx. 194 kΩ at 20˚C - 30˚C
Output terminal (Top grill heating element)
N.O of RY3 - A9
230V
Approx. 510 Ω
Output terminal (Bottom grill heating element)
N.O of RY4 - A9
230V
Approx. 534 Ω
Output terminal (Fan motor)
A9 - A5
230V
Approx. 875 Ω
Output terminal (Turntable motor and Oven lamp) A3 - N.O. OF RY1
230V
Approx. 186 Ω
Output terminal (Convection fan motor)
A9 - A7
230V
Approx. 223 Ω
Output terminal (Earth)
B2 - Chassis
-
0
TEST POINTS ON CONTROL UNIT
WARNING: DISCONNECT THE PLUG WHEN MEASURING RESISTANCE.
WARNING: WIRING / RE-WIRING.
Before carrying out any work; carry out 3D checks.
1. Disconnect the supply
2. Open the door and wedge open.
3. Discharge the high voltage capacitor.
Before carrying out any work; carry out 3D checks.
1. Disconnect the supply
2. Open the door and wedge open.
3. Discharge the high voltage capacitor.
RE-WIRING.
Ensure the following:
1. Wires must not touch:
Ensure the following:
1. Wires must not touch:
a) High voltage parts.
(Magnetron, high voltage transformer, high
voltage capacitor and high voltage rectifier).
voltage capacitor and high voltage rectifier).
b) Parts that become hot.
(Heating elements, oven lamp, oven cavity
magnetron and high voltage transformer).
magnetron and high voltage transformer).
c) Sharp edges.
(Bottom plates, oven cavity, waveguide
flange, chassis support and other
metallic parts).
flange, chassis support and other
metallic parts).
d) Movable parts.
( Fan blade, any motor, switch).
2. Positive lock connectors are fitted correctly. Ensure
the locking pin is located correctly.
3. Wires are connected correctly as per pictorial
diagram.
4. No wire leads are trapped by the outer wrap.
WIRING/RE-WIRING
R-8740M - 35
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2. COOKING TIME PROGRAMMED.
3. MICROWAVE POWER LEVEL KEY
1. DOOR CLOSED.
2. COOKING TIME PROGRAMMED.
3. MICROWAVE POWER LEVEL KEY
PRESSED ONCE (100%)
4. START KEY PRESSED.
Figure O-1 Oven Schematic-OFF Condition
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2.
1. DOOR CLOSED.
2.
:
OR CLOCK APPEARS ON DISPLAY.
NOTE: *INDICATES COMPONENTS WITH POTENTIALS ABOVE 250V
Figure O-2 Oven Schematic-Microwave Cooking Condition
NOTE: *INDICATES COMPONENTS WITH POTENTIALS ABOVE 250V
SCHEMATIC DIAGRAMS
/R-8740M
C1
C3
STOR
THERMI-
B2
B1
UNIT
CONTROL
F1:FUSE
*CAPACITOR
F2:FUSE
EARTH
*MAGNETRON
*POWER
TRANSFORMER
BLU
BRN
*ASYMMETRIC
RECTIFIER
*H.V. RECTIFIER
NEUTRAL
LIVE
NOISE SUPPRESSION COIL
NOISE
FILTER
/15
/15
G-Y/15
0.22 F/250V
N
L
10M/0.5W
4700u/250V
4700u/250V
680K/0.5W
GRILL HEATER (TOP)
OVEN
THERMAL
CUT-OUT
OVEN LAMP
OL
F8A
TM
T
MOTOR
TURNTABLE
CUT-OUT
THERMAL
MG
230V-240v 50Hz
N.C
SWITCH
MONITOR
20A
MONIT'D
LATCH
SWITCH
MOTOR
CONVECTION
CM
BOTTOM HEATER
FAN MOTOR
FM
RY4
A1
A3
A5
A9
A11
RY7
RY5
RY1
RY3
RY2
N.O
COM
N.O
COM
N.O
COM
1.07uF 2100V
/R-8740M
C1
C3
STOR
THERMI-
B2
B1
SWITCH
STOP
UNIT
CONTROL
F1:FUSE
*CAPACITOR
F2:FUSE
EARTH
*MAGNETRON
*POWER
TRANSFORMER
BLU
BRN
*ASYMMETRIC
RECTIFIER
*H.V. RECTIFIER
NEUTRAL
LIVE
NOISE SUPPRESSION COIL
NOISE
FILTER
/15
/15
G-Y/15
0.22 F/250V
N
L
10M/0.5W
4700u/250V
4700u/250V
680K/0.5W
GRILL HEATER (TOP)
OVEN
THERMAL
CUT-OUT
OVEN LAMP
OL
F8A
TM
T
MOTOR
TURNTABLE
CUT-OUT
THERMAL
MG
230-240V 50Hz
N.C
SWITCH
MONITOR
20A
MONIT'D
LATCH
SWITCH
MOTOR
CONVECTION
CM
BOTTOM HEATER
FAN MOTOR
FM
RY4
A1
A3
A5
A9
A11
RY7
RY5
RY1
RY3
RY2
N.O
COM
N.O
COM
N.O
COM
1.07uF 2100V
R-8740M - 36
SCHEMATIC DIAGRAMS
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2. COOKING TIME PROGRAMMED.
3. GRILL KEY PRESSED ONCE
4. START KEY PRESSED
1. DOOR CLOSED.
2. COOKING TIME PROGRAMMED.
3. GRILL KEY PRESSED ONCE
4. START KEY PRESSED
NOTE: *INDICATES COMPONENTS WITH POTENTIALS ABOVE 250V
Figure O-3(a) Oven Schematic-Grill Cooking Condition (TOP GRILL mode)
Figure O-3(b) Oven Schematic-Grill Cooking Condition (BOTTOM HEATER mode)
NOTE: *INDICATES COMPONENTS WITH POTENTIALS ABOVE 250V
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2. COOKING TIME PROGRAMMED.
3. GRILL KEY PRESSED TWICE.
4. START KEY PRESSED.
1. DOOR CLOSED.
2. COOKING TIME PROGRAMMED.
3. GRILL KEY PRESSED TWICE.
4. START KEY PRESSED.
R-8740M
C1
C3
STOR
THERMI-
B2
B1
SWITCH
STOP
UNIT
CONTROL
F1:FUSE
*CAPACITOR
F2:FUSE
EARTH
*MAGNETRON
*POWER
TRANSFORMER
BLU
BRN
*ASYMMETRIC
RECTIFIER
*H.V. RECTIFIER
NEUTRAL
LIVE
NOISE SUPPRESSION COIL
NOISE
FILTER
/15
/15
G-Y/15
0.22 F/250V
N
L
10M/0.5W
4700u/250V
4700u/250V
680K/0.5W
GRILL HEATER (TOP)
OVEN
THERMAL
CUT-OUT
OVEN LAMP
OL
F8A
TM
T
MOTOR
TURNTABLE
CUT-OUT
THERMAL
MG
230V-240V 50Hz
N.C
SWITCH
MONITOR
20A
MONIT'D
LATCH
SWITCH
MOTOR
CONVECTION
CM
BOTTOM HEATER
FAN MOTOR
FM
RY4
A1
A3
A5
A9
A11
RY7
RY5
RY1
RY3
RY2
N.O
COM
N.O
COM
N.O
COM
1.07uF 2100V
R-8740M
C1
C3
STOR
THERMI-
B2
B1
SWITCH
STOP
UNIT
CONTROL
F1:FUSE
*CAPACITOR
F2:FUSE
EARTH
*MAGNETRON
*POWER
TRANSFORMER
BLU
BRN
*ASYMMETRIC
RECTIFIER
*H.V. RECTIFIER
NEUTRAL
LIVE
NOISE SUPPRESSION COIL
NOISE
FILTER
/15
/15
G-Y/15
0.22 F/250V
N
L
10M/0.5W
4700u/250V
4700u/250V
680K/0.5W
GRILL HEATER (TOP)
OVEN
THERMAL
CUT-OUT
OVEN LAMP
OL
F8A
TM
T
MOTOR
TURNTABLE
CUT-OUT
THERMAL
MG
230V-240V 50Hz
N.C
SWITCH
MONITOR
20A
MONIT'D
LATCH
SWITCH
MOTOR
CONVECTION
CM
BOTTOM HEATER
FAN MOTOR
FM
RY4
A1
A3
A5
A9
A11
RY7
RY5
RY1
RY3
RY2
N.O
COM
N.O
COM
N.O
COM
1.07uF 2100V
Click on the first or last page to see other R-8740 (serv.man17) service manuals if exist.