R-652M - Sharp Home Appliance Service Manual (repair manual). Page 11

11

R-652M -

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 influ-
enced by the surrounding high voltage power source,
static electricity charge in clothes, etc., and some-
times 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 trans-
former, 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 be-

tween the touch control panel and the oven
itself is so short that the two can't be sepa-
rated.

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 be-

tween 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 con-
trols 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 con-

trol 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.