Operation - Sharp R-23GT-F Service Manual

Commercial microwave ovens
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R-23GT-F
R-24GT-F
The following is a description of component functions during
oven operation.
OFF CONDITION
Closing the door activates the door sensing switch and second-
ary interlock switches (1), (2). (In this condition, the monitor
switches (1) & (2) contacts are opened.) When the oven is
plugged in, and the rated voltage is supplied to the control unit
through the noise filter, (figure O-1), the display will show " .
".
IDLE CONDITION
When the door is opened, the contacts of the door sensing
switch open, initiating the following:
1. A signal is input to the control unit energizing the coil of shut-
off relay (RY-1).
2. The shut-off relay (RY-1) contacts close completing circuits
to turn on the oven lamp, blower motor and stirrer motors.
3. If the door remains open, 60 seconds later the control unit
de-energizes shut-off relay (RY-1) turning off the oven
lamp, blower motor and stirrer motors.
When the door is closed, the door sensing switch contacts
close. With the closing of the door sensing switch contacts, an
additional circuit is provided which will permit the operation of
the oven when one of the touch pads is depressed. Since the
control is enabled through the door sensing switch, the door
must be closed before the touch pads will be effective. When
the door is closed, a full 60 second IDLE condition is always
provided for selecting and pressing the desired touch pads. A
60 second IDLE condition will also follow the end of each cook
cycle.
COOKING CONDITION
When the door is closed from the open position and Memory
pad is touched the, following will occur:
1. The contacts of relays are closed and components connected
to the relays are turned on (For details, refer to Figure O-3)
2. Rated voltage is supplied to the primary winding of the
power transformer and is converted to about 3.1 volts
output on the filament winding, and approximately 2040
volts 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
channelled through the waveguide into the cavity feed-box,
and then into the cavity where the food is placed to be
cooked.
5. Upon completion of the cooking time, the oven will revert to
the IDLE condition.
6. When the door is opened during a cook cycle, monitor
switches (1) & (2), door sensing switch, secondary interlock
switches (1), (2) and primary interlock relays (1), (2) are
activated with the following results. The circuits to the high
voltage components are de-energized, and the digital read-
out displays " . " and cooking is cancelled (in the case of
Memory cooking).

OPERATION

DESCRIPTION OF OPERATING SEQUENCE
7. The monitor switch (1) is electrically monitoring the operation
of the secondary interlock switch (1) and primary interlock
relay (1), and monitor switch (2) is electrically monitoring the
operation of the secondary interlock switch (2) and primary
interlock relay (2), and monitor switches (1), (2) are
mechanically associated with the door so that it will function
in the following sequence.
(1) When the door opens from a closed position, the contacts
of the primary interlock relays (1), (2) and secondary
interlock switches (1), (2) open. Then the monitor switch
contacts close.
(2) When the door is closed from the open position, the monitor
switches (1), (2) contacts first open, and then the contacts
of the secondary interlock switches (1), (2) close.
If the secondary interlock switches (1), (2) and primary interlock
relays (1), (2) fail with their contacts closed when the door is
opened, the closing of the monitor switches (1), (2) contacts will
form a short circuit through the monitor fuse, secondary inter-
lock switches (1), (2) and primary interlock relays (1), (2),
causing the monitor fuse to blow.
VARIABLE POWER COOKING
When Variable Cooking Power is programmed, the rated
voltage A.C. is supplied to the power transformer intermittently
through the contacts of relay (RY-2, RY-3). Relays RY-2 and
RY-3 are operated by the control unit within an interval second
time base. Microwave power operation is as follows:
POWER LEVEL
100%
90%
80 %
70%
60%
50%
40%
30%
20%
10%
0%
Note: The ON/OFF time ratio does not exactly correspond
with the percentage of microwave power, because
approx. 2 seconds are needed for heating of the
magnetron filament.
6
ON TIME
OFF TIME
32 sec.
0 sec.
30 sec.
2 sec.
26 sec.
6 sec.
24 sec.
8 sec.
22 sec.
10 sec.
18 sec.
14 sec.
16 sec.
16 sec.
12 sec.
20 sec.
8 sec.
24 sec.
6 sec.
26 sec.
0 sec.
32 sec.

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