Section 2 Operation; Operating Sequence Description; Off Condition; Cooking Condition - Electrolux FGMO205KFA Service Manual

Operating Sequence Description

The following is a description of component functions
during oven operation.

OFF CONDITION

Closing the door activates the door sensing switch and
secondary interlock switch. (In this condition, the
monitor switch contacts are opened.) When oven is
plugged in, 120 volts AC is supplied to the control unit.
(Figure 2-1).
1. The display will show "ENJOY YOUR OVEN PRESS
CLEAR AND PRESS CLOCK". To set any program or
set the clock, you must first touch the STOP/CLEAR
button. The display will clear, and " : " appears.

COOKING CONDITION

Program desired cooking time by touching the NUMBER
pads. Program the power level by touching the POWER
LEVEL pad and then a NUMBER pad. When the START
pad is touched, the following operations occur:
1. The contacts of relays are closed and components
connected to the relays are turned on as follows.
(For details, refer to Figure 2-2)
RELAY CONNECTED COMPONENTS
RY1 Oven Lamp / Turntable Motor / Fan motor
RY2 Power Transformer
2. 120 volts AC is supplied to the primary winding of
the power transformer and is converted to about
3.3 volts AC output on the filament winding, and
approximately 2370 volts AC on the high voltage
winding.
3. The filament winding voltage heats the magnetron
filament and the H.V. winding voltage is sent to a
voltage doubler circuit.
4. The microwave energy produced by the magnetron
is channeled through the waveguide into the cavity
feedbox, and then into the cavity where the food
is placed to be cooked.
5. Upon completion of the cooking time, the power
transformer, oven lamp, etc. are turned off, and the
generation of microwave energy is stopped. The
oven will revert to the OFF condition.
6. When the door is opened during a cook cycle, the
monitor switch, door sensing switch, primary
interlock switch, relay (RY1) and secondary
interlock relay are activated with the following
results. The circuits to the turntable motor, the
cooling fan motor, and the high voltage components
are de-energized, the oven lamp remains on, and
the digital read-out displays the time still remaining
in the cook cycle when the door was opened.
7. The monitor switch electrically monitors the
operation of the primary interlock switch and
secondary interlock relay and is mechanically
associated with the door so that it will function in
the following sequence.
(1) When the door opens from the closed position,
the secondary interlock relay (RY2) and primary
interlock switch open their contacts, and the
contacts of the relay (RY1) remains closed.
Then the monitor switch contacts close.
(2) When the door is closed from the open position,
the monitor switch contacts open first. Then
the contacts of the primary interlock switch and
door sensing switch close, and the contacts of
the relay (RY1) open.
If the primary interlock switch and secondary interlock
relay (RY2) fail with the contacts closed when the door
is opened, the closing of the monitor switch contacts will
form a short circuit through the monitor fuse, primary
interlock switch, relay (RY1) and secondary interlock
relay (RY2), causing the monitor fuse to blow.

Section 2 Operation

2-1