Sharp R-741M (serv.man2) Service Manual ▷ View online
5
741M -
TEST PROCEDURES
PROCEDURE
LETTER
A
TOUCH CONTROL PANEL ASSEMBLY TEST
COMPONENT TEST
The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlike conventional microwave ovens, proper maintenance can not be performed with only a voltmeter
and ohmmeter.
In this service manual, the touch control panel assembly is in one unit and troubleshooting by unit
replacement is described according to the symptoms indicated.
Control Panel.
unlike conventional microwave ovens, proper maintenance can not be performed with only a voltmeter
and ohmmeter.
In this service manual, the touch control panel assembly is in one unit and troubleshooting by unit
replacement is described according to the symptoms indicated.
Control Panel.
The following symptoms indicate a defective control unit.
1. Tact Switch.
The following symptoms indicate a defective tact switch. Replace the tact switch.
a) When touching a tact switch, a certain tact switch produces no signal at all.
b) When touching a tact switch, sometimes a tact switch produces no signal.
b) When touching a tact switch, sometimes a tact switch produces no signal.
2. In connection with tact switches.
a) When touching a tact switch, a certain group of tact switch do not produce a signal.
b) When touching a tact switch, no tact switch produce a signal.
b) When touching a tact switch, no tact switch produce a signal.
3. Display problems.
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 up.
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.
h) When touching a tact switch, the control unit does not respond.
b) At a certain digit, brightness is low.
c) Only one indicator does not light up.
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.
h) When touching a tact switch, the control unit does not respond.
4. Other possible problems caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Cooking is not possible.
b) Cooking is not possible.
1. Disconnect the oven from the power supply.
2. Discharge the high voltage capacitor.
3. Remove the control unit from the control panel.
4. By using an ohmmeter, check the tact switch operation.
5. When the tact switch is not depressed, an ohmmeter should indicate an open circuit. When the tact
2. Discharge the high voltage capacitor.
3. Remove the control unit from the control panel.
4. By using an ohmmeter, check the tact switch operation.
5. When the tact switch is not depressed, an ohmmeter should indicate an open circuit. When the tact
switch is depressed, an ohmmeter should indicate a short circuit. If improper operation is indicated,
the tact switch is probably defective and should be checked.
the tact switch is probably defective and should be checked.
B
TACT SWITCH TEST
C
RELAY TEST
1. CARRY OUT 3D CHECKS.
2. Disconnect the leads from the primary of the high voltage transformer. Make sure that the leads
2. Disconnect the leads from the primary of the high voltage transformer. Make sure that the leads
remain isolated from other oven components and chassis. (Use insulation tape if necessary.)
3. Close the door.
4. Reconnect the supply.
5. Check the voltage between Pin Nos. 1 and 3 of the 3 pin connector (A) on the control unit with an
4. Reconnect the supply.
5. Check the voltage between Pin Nos. 1 and 3 of the 3 pin connector (A) on the control unit with an
A.C. voltmeter. The meter should indicate 230-240 volts, if not check oven circuit.
6. RY1, RY2 and RY3 TEST
These are operated by D.C. voltage. Check voltage at the relay coil with a D.C. voltmeter during the
These are operated by D.C. voltage. Check voltage at the relay coil with a D.C. voltmeter during the
microwave 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,
DC. voltage not indicated ........ Check diode which is connected to the relay coil. If diode is good,
control unit is defective.
6
741M -
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
D
PROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE PRINTED WIRING
BOARD (PWB) IS OPEN
To protect the electronic circuits, this model is provided with a fine foil pattern added to the primary on
the PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the troubleshooting guide given
below for repair.
the PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the troubleshooting guide given
below for repair.
Problem: POWER ON, indicator does not light up.
CARRY OUT 3D CHECKS.
STEPS
OCCURANCE
CAUSE OR CORRECTION
1
The rated AC voltage is not present at
Check supply voltage and oven power cord.
POWER terminal of connector (CN-A).
2
The rated AC voltage is present at primary
Low voltage transformer or secondary circuit defective.
side of low voltage transformer.
Check and repair.
3
Only pattern at "a" is broken.
*Insert jumper wire J1 and solder.
(CARRY OUT 3D CHECKS BEFORE REPAIR)
4
Pattern at "a" and "b" are broken.
*Insert the coil RCILF2003YAZZ between "c" and "d".
See NOTE : 2.
(CARRY OUT 3D CHECKS BEFORE REPAIR)
NOTE : 1
*At the time of these repairs, make a
visual inspection of the varistor for
burning damage and examine the
transformer with tester for the pres-
ence of layer short-circuit (check pri-
mary coil resistance). If any abnor-
mal condition is detected, replace
the defective parts.
visual inspection of the varistor for
burning damage and examine the
transformer with tester for the pres-
ence of layer short-circuit (check pri-
mary coil resistance). If any abnor-
mal condition is detected, replace
the defective parts.
NOTE : 2
The hole "C" is not prepared for the
coil on this PWB. So, insert the coil
instead of J1 at first. Then solder the
one lead wire of the coil at "d". And
solder the other lead wire of the coil
at the Pin No.1 of the connector CN-
A.
coil on this PWB. So, insert the coil
instead of J1 at first. Then solder the
one lead wire of the coil at "d". And
solder the other lead wire of the coil
at the Pin No.1 of the connector CN-
A.
CARRY OUT 4R CHECKS.
VRS1
a
b
c
d
D20
WH - 3
A
5
1
AC
CN - A
OL/FM
/TTM
/TTM
(J1)
D21
RY1
See NOTE : 2
Lead wire of coil
Lead wire of coil
RELAY SYMBOL
OPERATIONAL VOLTAGE
CONNECTED COMPONENTS
RY1
APPROX. 24.0V D.C.
Oven lamp / Turntable motor / Cooling fan motor
RY2
APPROX. 18.0V D.C.
Grill heater
RY3
APPROX. 18.0V D.C.
High voltage transformer
7
741M -
TOUCH CONTROL PANEL ASSEMBLY
OUTLINE OF TOUCH CONTROL PANEL
The touch control section consists of the following circuits as
shown in the touch control panel circuit.
shown in the touch control panel circuit.
The principal functions of these circuits and their related
signals are explained below.
signals are explained below.
Tact Switch
Signals generated in the LSI are sent to the tact switches
through SEG0, SEG1, SEG2, and SEG3.
When a tact switch is touched, a signal is completed through
the tact switch and passed back to the LSI through P20 and
P23 to perform the function that was requested.
through SEG0, SEG1, SEG2, and SEG3.
When a tact switch is touched, a signal is completed through
the tact switch and passed back to the LSI through P20 and
P23 to perform the function that was requested.
Control Unit
Control unit consists of LSI, ACL circuit, indicator circuit,
power source circuit, relay circuit, buzzer circuit, synchroniz-
ing signal circuit and back light circuit.
power source circuit, relay circuit, buzzer circuit, synchroniz-
ing signal circuit and back light circuit.
1) LSI(I-1)
This LSI controls the tact switch strobe signal, relay
driving signal for oven function and indicator signal.
driving signal for oven function and indicator signal.
2) ACL
This circuit generates a signal which resets the LSI to the
initial state when power is supplied.
initial state when power is supplied.
3) Indicator Circuit
This circuit consists of 4-digits, 12-segments and 3-
common electrodes using a Liquid Crystal Display.
common electrodes using a Liquid Crystal Display.
4) Power Source Circuit
This circuit generates voltage necessary in the control
unit from the AC line voltage.
unit from the AC line voltage.
Symbol
Voltage
Application
VC
- 5V
LSI(IC1)
5) Relay Circuit
To drive the magnetron, grill heater, fan motor, turntable
motor and light the oven lamp.
motor and light the oven lamp.
6) Buzzer Circuit
The buzzer is responsive to signals from the LSI to emit
audible sounds (tact switch touch sound and completion
sound).
audible sounds (tact switch touch sound and completion
sound).
7) Synchronizing Signal Circuit
The power source synchronizing signal is available in
order to compose a basic standard time in the clock
circuit. It accompanies a very small error because it
works on commercial frequency.
order to compose a basic standard time in the clock
circuit. It accompanies a very small error because it
works on commercial frequency.
8) Door Sensing Switch
A switch to "tell" the LSI if the door is open or closed.
9) Back Light Circuit
A circuit to drive the back light (Light emitting diodes
LED1-LED4)
LED1-LED4)
8
741M -
TOUCH CONTROL ASSEMBLY/DESCRIPTION OF LSI
LSI(IZA918DR)
The I/O signal of the LSI(IZA918DR) are detailed in the following table.
Pin No.
Signal
I/O
Description
1-7
SEG13 -
OUT
Segment data signal.
SEG19
Connected to LCD.
The relation between signals are as follows:
LSI signal (Pin No.)
The relation between signals are as follows:
LSI signal (Pin No.)
LCD
LSI signal (Pin No.) LCD
SEG 13 (1) ..................................... S7
SEG 19 (7) .................................. S1
SEG 14 (2) ..................................... S6
SEG 8 (59) ................................ S12
SEG 15 (3) ..................................... S5
SEG 9 (60) ................................ S11
SEG 16 (4) ..................................... S4
SEG 10 (61) .............................. S10
SEG 17 (5) ..................................... S3
SEG 11 (62) ................................ S9
SEG 18 (6) ..................................... S2
SEG 12 (63) ................................ S8
8
NC
Not connection terminal.
9
NC
Connected to COM2 (LSI Pin No, 49).
10
NC
Connected to COM1 (LSI Pin No, 48).
11
NC
Connected to COM0 (LSI Pin No, 47).
12-13
NC
No connection terminal.
14-16
VC1-VC3
IN/OUT
Terminal not used.
17
XRESET
IN
Auto clear terminal.
Signal is input to reset the LSI to the initial state when power is supplied. Temporarily
set "L" level the moment power is supplied, at this time the LSI is reset. Thereafter
set at "H" level.
set "L" level the moment power is supplied, at this time the LSI is reset. Thereafter
set at "H" level.
18
XTEST
IN
Connected to GND.
19
VSS
IN
Power source voltage: -5V.
Power source voltage is applied to drive the LSI.
20
OSC1
IN
Internal clock oscillation frequency setting input.
The internal clock frequency is set by inserting the ceramic filter oscillation circuit with
respect to OSC2 terminal.
respect to OSC2 terminal.
21
OSC2
OUT
Internal clock oscillation frequency control output.
Output to control oscillation input of OSC1.
22
VD1
IN
Power source voltage input terminal.
Power source voltage is applied to drive the oscillation circuit which makes the clock
signal in the LSI.
signal in the LSI.
23
VDD
IN
Power source voltage: 0V.
Power source voltage is applied to drive the LSI.
24
AVDD
IN
Power source voltage input terminal.
Power source voltage is applied to drive the A/D converter in the LSI. Connected to
GND.
GND.
25
AVREF
IN
Reference voltage input terminal.
A reference voltage is applied to drive the A/D converter in the LSI. Connected to
GND.
GND.
26
AVSS
IN
Power source voltage input terminal.
Power source voltage is applied to drive the A/D converter in the LSI. Connected to
VC. (-5V)
VC. (-5V)
27-28
NC
No connection terminal. (Connected to VC (-5V))
29-32
R40-R43
IN
Terminal to change functions according to the Model.
By using the A/D converter contained in the LSI, DC voltage in accordance with the
Model in operation is applied to set up its function.
Model in operation is applied to set up its function.
33
NC
No connection terminal.
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