R-890SLM
9 - 2
[2] SERVICING FOR CONTROL PANEL
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 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
2. Servicing of Control Panel
We describe the procedures to permit servicing of the control
panel of the microwave oven and the precautions you must take
when doing so. To perform the servicing, power to the control
panel is available either from the power line of the oven or from
an external power source.
1) Servicing the 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 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 control panel,
(1) Disconnect the power supply cord.
(2) Open the door and block it open.
(3) Reconnect the leads to the primary of the power
transformer.
(4) Reinstall the outer case (cabinet).
(5) Reconnect 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
control panel and the oven is so short that the two
can’t be separated.
For those models, check and repair all the controls
(sensorrelated ones included) of the control panel
while keeping it connected to the oven.
b) On some models, the power supply cord between the
control panel and the oven 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 control panel while keeping it apart from the
oven; in this case you must short both ends of the door
sensing switch (on PWB) of the 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 control panel, checking
them is possible if the dummy resistor(s) with resistance
equal to that of the controls are used.
2) Servicing the control panel with power supply from an
external power source:
Disconnect the control panel completely from the oven, and
short both ends of the door sensing switch (on PWB) of
the 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
control panel, then it is possible to check and repair the
controls of the control panel; it is also possible to check the
sensor-related controls of the control panel by using the
dummy resistor(s).
3. Servicing Tools
Tools required to service the control panel assembly.
1) Soldering iron: 60W
(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 connector of the switch 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.
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4/25/09 10:55:27 AM
