Sharp R-21LCF - Oven Microwave 1000 W Service Manual Download Page 9

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R21LCF

6 – 1

R21LCF

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 the noise filter
and the control unit (Figure O-1).

2. COOKING CONDITION

When the Light Up Dial is turned, 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 (RY2) and pri-
mary interlock relay (RY1) 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 (RY1) 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 (RY1) and secondary interlock switch open their
contacts. 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.

If the secondary interlock switch and primary interlock relay (RY1) 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, and primary interlock relay(RY1),
causing the monitor fuse to blow.

[2] OVEN SCHENATIC

1. Off Condition

Figure O-1. Oven Schematic-Off Condition

RELAY CONNECTED

COMPONENTS

RY-1

oven lamp/antenna motor/fan motor

RY-2 power

transformer

SCHEMATIC

NOTE: CONDITION OF OVEN
1. LIGHT UP DIAL OFF.
2. DOOR CLOSED.

FUSE