Electrolux EI30SM55JB Technical & Service Manual page 47

Servicing of Touch Control Panel
The following are descriptions of 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:
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 performance of 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.
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.
Component Teardown and Testing
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 brings about an operational state that is
equivalent to the oven door being closed. Connect
an externa 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).
Servicing Tools
Tools required to service the touch 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
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.
4-9