Sharp SMD2499FS Service Manual page 9

The following is a description of component functions during
oven operation.
OFF CONDITION
Closing the door activates the door sensing switch and
primary interlock switch. (In this condition, the monitor switch
contacts are opened.)
When oven is plugged in, 120 volts A.C. is supplied to the
control unit. (Figure O-1).
1. The display will show "ENJOY YOUR OVEN TOUCH
CLEAR".
To set any program or set the clock, you must first touch the
STOP/CLEAR pad. The display will clear, and " : " will appear.
NOTE: When the door is opened, the oven lamp comes on.
2. A signal is input to the control unit, energizing the coil
of shut-off relay (RY-11 and RY-12). RY-11 and RY-12
contacts close, completing a circuit to the damper motor.
The damper motor now operates moving the damper to the
open position, thereby closing the contacts of the damper
switch inputs a signal to the control unit. The coil of relay
RY-11 and RY-12 is de-energized, opening its contacts,
there by turning off the damper motor.
MICROWAVE COOKING CONDITION
Program desired cooking time Variable Cooking Control by
touching the NUMBER pads and the power level pad.
When the START pad is touched, the following operations
occur:
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.
RELAY CONNECTED COMPONENTS
RY1 High voltage transformer and all heating elements
RY2 High voltage transformer
RY9 Stirrer motor
RY10 Fan motor
RY14 MG Fan motor
2. 120 volts A.C. is supplied to the primary winding of the
power transformer and is converted to about 3 volts A.C.
output on the filament winding, and approximately 2360
volts A.C. 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 double
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.
OPERATION
DESCRIPTION OF OPERATING SEQUENCE
6. When the door is opened during a cook cycle, third door
switch (only Canada model), monitor switch, door sensing
switch, the secondary interlock relay and the primary
interlock switch are activated with the following results.
The circuits to the stirrer motor and the high voltage
components are de-energized, the oven lamp remains
on, and the digital read-out displays the time remaining
in the cook cycle when the door was opened.
7. The monitor switch is electrically monitoring the operation
of the secondary interlock relay (RY1) and the primary
interlock switch and is mechanically associated with the
door so that it will function in the following sequence:
(1) When the door opens from a closed position, the door
sensing switch and the primary interlock switch open their
contacts, and then the monitor switch contacts close and then
the third door switch (only Canada model) contacts open.
(2) When the door is closed from the open position, the
monitor switch contacts open, and the third door switch (only
Canada model) contacts close first, and then the contacts of
the primary interlock switch and the door sensing switch close.
If the secondary interlock relay (RY1) and the primary interlock
switch fail with their contacts closed when the door is opened,
the closing of the monitor switch contacts will form a short
circuit through the monitor fuse, the secondary
interlock relay (RY1) and the primary interlock switch, causing
the monitor fuse to blow.
POWER LEVEL P-0 TO P-90 COOKING
When Variable Cooking Power is programmed, the 120 volts
A.C. is supplied to the power transformer intermittently through
the contacts of relay (RY-1). RY-1 is operated by the control
unit within a varying time base. Microwave power operation
is as follows:
VARI-MODE
Power 10(P-HI)
(100% power)
Power 9(P-90)
(approx. 90% power)
Power 8(P-80)
(approx. 80% power)
Power 7(P-70)
(approx. 70% power)
Power 6(P-60)
(approx. 60% power)
Power 5(P-50)
(approx. 50% power)
Power 4(P-40)
(approx. 40% power)
Power 3(P-30)
(approx. 30% power)
Power 2(P-20)
(approx. 20% power)
Power 1(P-10)
(approx. 10% power)
Power 0(P-0)
(0% power)
Note: The ON/OFF time ratio does not correspond with the
percentage of microwave power, because approx. 2 seconds
are needed for heating of the magnetron filament.
9
SMD2499FS
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.