R-753 (serv.man3). Complete - Sharp Home Appliance Service Manual (repair manual). Page 13

12

753M -

approx. 1M ohm

This unit uses CMOS LSI in the integral part of the
circuits. When handling these parts, the following
precautions should be strictly followed. CMOS LSI
have extremely high impedance at its input and output
terminals. 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 external power source.

Therefore, when checking the performance of the
touch control panel, put the outer cabinet on the
oven to avoid touching the high voltage transformer,
or unplug the primary terminal (connector) of the
high voltage transformer to turn it off; the end of
such connector must be insulated with an insulating
tape. After servicing, be sure to replace the leads to
their original locations.

 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.

 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 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.

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 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 touch control panel by using the dummy
resistor(s).

Tools required to service the touch control panel
assembly.
1) Soldering iron: 30W

(It is recommended to use a soldering iron with a
grounding terminal.)

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 terminals.

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.