R-959SLMA (serv.man9). Touch Control Panel Assembly - Sharp Home Appliance Service Manual (repair manual)

R959(SL)MA

9 – 1

R959(SL)MA

Service Manual

 

The control section consists of the following units as shown in the con-
trol panel circuit.

(1) Key Unit

(2) Control Panel Unit (The Control panel unit consists of Power unit
and Control unit.)

The principal functions of these units and signals communicated
among them are explained below.

The key unit is composed of a matrix, signals generated in the LSI are
sent to the key unit from P50 – P57. When a key pad is touched, a sig-
nal is completed through the key unit and passed back to the LSI
through P44 – P47 to perform the function that was requested.

Control unit consists of LSI, power source circuit, synchronizing signal
circuit, ACL circuit, buzzer circuit, relay circuit, temperature measure-
ment circuit, indicator circuit, absolute humidity sensor circuit and back
light circuit.

1) LSI

This LSI controls the temperature measurement signal, tact switch
strobe signal, relay driving signal for oven function and indicator
signal.

2) Power Source Circuit

This circuit generates voltage necessary in the control unit.

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) ACL

A circuit to generate a signal which resets the LSI to the initial state
when power is supplied.

5) Buzzer Circuit

The buzzer is responsive to signals from the LSI to emit audible
sounds (key touch sound and completion sound).

6) Door Sensing Switch (Stop Switch)

A switch to “tell” the LSI if the door is open or closed.

7) Relay Circuit

To drive the magnetron, grill heating element, convection heating
element, convection motor, fan motor, turntable motor, damper
motor, touch control transformer and light the oven lamp.

8) Back Light Circuit

A circuit to drive the back light (Light emitting diodes LD10 - LD19).

9) Indicator Circuit

This circuit consists 40-segments and 16-common electrodes using
a Liquid Crystal Display. 

The Liquid Crystal Display (LCD) is drive by LCD driver IC3.

10)Temperature Measurement Circuit: (OVEN THERMISTOR)

The temperature in the oven cavity is sensed by the thermistor. The
variation of resistance according to sensed temperature is detected
by the temperature measurement circuit and the result applied to
LSI. The LSI uses this information to control the relay and display
units.

11)Damper Switch

A switch to tell the LSI if the damper is open or close.

12)Energy Save Mode Circuit

A circuit to drive the touch control transformer. If the oven has not
been used for 3 minutes or more, the circuit will be opened and the
control unit will not be energized.

Symbol

Voltage

Application

VC

-5.2V

LSI(IC1)

R959(SL)MA

9 – 2

This unit uses CMOS LSI in the integral part of the circuits. When han-
dling these parts, the following precautions 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 electricity charge in clothes, etc., and
sometimes it is not fully protected 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 containing them in aluminium foil.

2) When soldering, ground the technician as shown in the figure and

use grounded soldering iron and work table.

We describe the procedures to permit 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

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 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.

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 touch

control panel and the oven itself is so short that the two can't be
separated. For those models, check and repair all the controls
(sensor-related ones included) 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 long enough that they may
be separated from each other. For those models, therefore, it is
possible to check 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
operational state that is equivalent 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

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. Connect an exter-
nal 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 touch control panel by using the dummy resistor(s).

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

1) Before turning on the power source of the control unit, remove the

aluminium foil applied for preventing 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.

approx. 1M ohm