Service manual

7
R-1855A
OPERATION
DESCRIPTION OF OPERATING SEQUENCE
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 A.C. is supplied to the
control unit. (Figure O-1).
1. The display will show , , ,
, , , , and
.
To set any program or set the clock, you must first touch
the STOP/CLEAR pad. The display will clear, and " : "
will appear.
COOKING CONDITION
Program desired cooking time touching the NUMBER pads.
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 O-2)
RELAY CONNECTED COMPONENTS
RY1 Oven lamp
RY2 Power transformer/ Stirrer motor
RY4 Turntable motor
RY5 Fan motor
2. 120 volts A.C. is supplied to the primary winding of the
power transformer and is converted to about 3.3 volts
A.C. output on the filament winding, and approximately
2000 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 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 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, monitor
switch, door sensing switch, secondary interlock switch
and third door switch and primary interlock relay are
activated with the following results. The circuits to the
stirrer motor, the cooling fan motor, the turntable motor,
and the high voltage components are de-energized, and
the digital read-out displays the time still remaining in the
cook cycle when the door was opened.
7. The monitor switch is electrically monitoring the operation
of the secondary interlock switch, third door switch and
door sensing switch 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
primary interlock relay, door sensing switch,
secondary interlock switch and third door switch
open their contacts, and then the monitor switch
contacts close.
(2) When the door is closed from the open position, the
monitor switch contacts first open, and then the
contacts of the secondary interlock switch and third
door switch close.
If the secondary interlock switch, third door switch and door
sensing 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, third door
switch, secondary interlock switch and primary interlock
relay, 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 intermit-
tently through the contacts of relay (RY2) which is operated
by the control unit within an interval second time base.
Microwave power operation is as follows:
VARI-MODE ON TIME OFF TIME
Power 10(P-HI) 32 sec. 0 sec.
(100% power)
Power 9(P-90) 30 sec. 2 sec.
(approx. 90% power)
Power 8(P-80) 26 sec. 6 sec.
(approx. 80% power)
Power 7(P-70) 24 sec. 8 sec.
(approx. 70% power)
Power 6(P-60) 22 sec. 10 sec.
(approx. 60% power)
Power 5(P-50) 18 sec. 14 sec.
(approx. 50% power)
Power 4(P-40) 16 sec. 16 sec.
(approx. 40% power)
Power 3(P-30) 12 sec. 20 sec.
(approx. 30% power)
Power 2(P-20) 8 sec. 24 sec.
(approx. 20% power)
Power 1(P-10) 6 sec. 26 sec.
(approx. 10% power)
Power 0(P-0) 0 sec. 32 sec.
(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.
CONVECTION COOKING CONDITION
PREHEATING CONDITION
Program desired convection temperature by touching the
PREHEAT pad and the temperature pad.