R-21AT - Sharp Home Appliance Service Manual (repair manual). Page 19

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approx. 1M ohm

IC
KIA7805P1

Transistor
DTA123ES
DTB143ES
DTC143ES
DTD143ES

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 in-
cluded) 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 dummy
resistor(s) with resistance equal to that of the controls
are used.

ply from an external power source:
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 equiva-
lent 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: 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

5. Other Precautions
1) Before turning on the power source of the control unit,

remove the aluminium foil applied for preventing static
electricity.

2) Connect the connectors 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 abnor-

mal 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.

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 elec-
tricity 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 all 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.

ply of the oven:
CAUTION:
THE HIGH VOLTAGE TRANSFORMER OF THE
MICROWAVE OVEN IS STILL LIVE DURING SERV-
ICING PRESENTS A HAZARD.
Therefore, before checking the performance of the
touch control panel,
1) Disconnect the power supply cord, and then re-

move 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