R21LTF
6 – 1
R21LTF
Service Manual
CHAPTER 6.
OPERATION
[1] DESCRIPTION OF OPERATING SEQUENCE
The following is a description of component functions during oven operation.
1. OFF CONDITION
Closing the door activates door sensing switch and secondary inter-
lock switch. (In this condition, the monitor switch contacts are opened.)
When oven is plugged in, 120 volts A.C. is supplied to noise filter of
the control unit (Figure O-1).
1) The display will show " . ".
2. COOKING CONDITION
Program desired cooking time by touching SELECTATIME pad and
the NUMBER pads. When the START pad is touched, the following
operations occur:
1) The contacts of the relays are closed and components connected
to the relays are turned on as follows.
(For details, refer to Figure O-2)
2) 120 volts A.C. is supplied to the primary winding of the power trans-
former and is converted to about 3.2 volts A.C. output on the fila-
ment winding, and approximately 2150 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, relay (RY3) and pri-
mary interlock relay (RY2) are activated with the following results.
The circuits to the antenna 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 sec-
ondary interlock switch and control relay (RY3) and is mechanically
associated with the door so that it will function in the following
sequence.
a) When the door opens from the closed position, the primary
interlock relay (RY2) and secondary interlock switch open their
contacts. And contacts of the relay (RY3) remains closed. Then
the monitor switch contacts close.
b) When the door is closed from the open position, the monitor
switch contacts open first. Then the contacts of the secondary
interlock switch and door sensing switch close and contacts of
the relay (RY3) open.
If the secondary interlock switch and primary 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, secondary interlock switch, relay (RY3) and primary interlock
relay (RY2), causing the monitor fuse to blow.
3. POWER LEVEL P-0 TO P-90 COOKING (R-21LTF
only)
When Variable Cooking Power is programmed, the 120 volts A.C. is
supplied to the power transformer intermittently through the contacts of
relay (RY-2) which is operated by the control unit within a 32 second
time base. Microwave power operation is as follows:
NOTE:
The ON/OFF time ratio does not correspond with the per-
centage of microwave power, because approx. 2 seconds
are needed for heating of the magnetron filament.
RELAY CONNECTED
COMPONENTS
RY-2 power
transformer
RY-3
oven lamp/antenna motor/fan motor
VARI-MODE ON
TIME
OFF
TIME
Power 10 (P-HI) (100% power)
32 sec.
0 sec.
Power 9 (P-90) (approx. 90% power)
30 sec.
2 sec.
Power 8 (P-80) (approx. 80% power)
26 sec.
6 sec.
Power 7 (P-70) (approx. 70% power)
24 sec.
8 sec.
Power 6 (P-60) (approx. 60% power)
22 sec.
10 sec.
Power 5 (P-50) (approx. 50% power)
18 sec.
14 sec.
Power 4 (P-40) (approx. 40% power)
16 sec.
16 sec.
Power 3 (P-30) (approx. 30% power)
12 sec.
20 sec.
Power 2 (P-20) (approx. 20% power)
8 sec.
24 sec.
Power 1 (P-10) (approx. 10% power)
6 sec.
26 sec.
Power 0 (P-0) (0% power)
0 sec.
32 sec.
