Sharp R-1870 User Manual download pdf (Page 8)

R-1870

R-1871

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 SHARP, SIMPLY, THE, BEST,

PRESS, CLEAR, and PRESS, CLOCK.

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, primary switch and secondary

switch and secondary 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 primary and secondary switch and secondary

interlock relay 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

secondary interlock relay, door sensing switch, primary

and secondary 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 primary and secondary switch close.

If the primary switch, secondary switch and secondary

interlock relay 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, secondary

switch switch, primary switch and secondary 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

intermittently 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.

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Sharp R-1870 User Manual Page 8

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