Touch Control Panel Servicing - Wolf MWD24-2 Service Manual

Drawer Microwave

TOUCH CONTROL PANEL SERVICING

1. Precautions for Handling Electronic Components: This unit uses CMOS LSI in the integral part of the cir-
cuits. 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 sur-
rounding high voltage power source, static electricity charge in clothes, etc. and sometimes it is not fully protect-
ed by the built-in protection circuit.
In Order to Protect The CMOS LSI: When storing and transporting, thor-
oughly wrap them in aluminum foil. Also wrap all PW boards containing
them in aluminum foil. When soldering, ground the technician as shown in
the illustration to the right and use grounded soldering iron and work table.
2. Servicing of Touch Control Panel: We describe the procedures to permit
servicing of the touch control panel of the microwave oven and the precau-
tions 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.
A. Servicing the touch control panel with power supply of the oven, therefore, before checking the performance
of the touch control panel you must:
THE HIGH VOLTAGE TRANSFORMER OF MICROWAVE OVEN IS STILL LIVE DURING SERVICING AND PRE-
SENTS A HAZARD.
• Disconnect the power supply cord, and then remove the outer case.
• Open the door and block it open.
• Discharge high voltage capacitor. (See Figure 4-1 on page 4-3 of this section)
• Disconnect the leads to the primary of the power transformer.
• Ensure that these leads remain isolated from other components and oven chassis by using insulation
tape.
• Re-connect the power supply cord.
B. After checking the performance of the touch control panel:
• Disconnect the power supply cord.
• Open the door and block it open.
• Re-connect the leads to the primary of the power transformer.
• Re-install the outer case (cabinet).
• Re-connect the power supply cord after the outer case is installed.
• Run the oven and check all functions.
C. 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 controls (sensor-related ones included) of
touch control panel while keeping it connected to the oven.
D. On some models, the power supply cord between touch control panel and 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
touch control panel while keeping it apart from 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, check-
ing them is possible if dummy resistor(s) with resistance equal to that of the controls are used.
2. Servicing Touch Control Panel with Power Supply from an External Power Source: Disconnect touch con-
trol 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 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.
• Soldering iron: 30W (It is recommended to use a soldering iron with a grounding terminal.)
• Oscilloscope: Single beam, frequency range: DC-0MHz type or more advanced model.
• Others: Hand tools
(Models MWD24-2 / MWD30-2)
4-5
Component Access
approx. 1M ohm
#813632 - Revision B - December, 2009