R-242M - Sharp Home Appliance Service Manual (repair manual). Page 11

R-242M - 11

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.

approx. 1M ohm

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

Transistor
2SA1267Y
KRA101M
KRC101M
KRC105M

(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.