Sharp R-305EW Service Manual download pdf (Page 23)

R-305EW

1. Precautions for Handling Electronic Components

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 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.

approx. 1M ohm

TOUCH CONTROL PANEL SERVICING

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, 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 activates 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.

(2) Servicing the touch control panel with power supply

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

activates 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).

3. Servicing Tools

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

4. 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 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.

2. Servicing of Touch Control Panel

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.

(1) Servicing the touch control panel with power supply

of the oven:

CAUTION:

THE HIGH VOLTAGE TRANSFORMER OF THE

MICROWAVE 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.

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Sharp R-305EW Service Manual Page 23

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