Sharp Carousel II R-3A54 Service Manual - Page 7

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R-3A54

R-3E54

FUNCTION

OF IMPORTANT

COMPONENTS

DOOR

OPEN

MECHANISM

The door can be opened

by pushing

the door open

button

on the control

panel. When the door open but-

ton is pushed, the switch

lever is moved

upward,

op-

erating

the

latch

head.

The

latch

head

is moved

upward,

and released from the latch hook.

Now, the

door can be opened.

Door--&+

Switch

lever

Stop switch

Figure

D-l.

Door Open Mechanism

IST

LATCH,

2ND

LATCH

AND

STOP

SWITCHES

1. When the oven door is closed, the contacts

(COM

2. When the oven door is opened, the contacts

(COM

-NO)

must be opened.

-NO)

must be closed.

MONITOR

SWITCH

1. When

the

oven

door

closed,

the

contacts

(COM-NC)

must be opened.

2. When

the

oven

door

is opened,

the

contacts

(COM - NC) must be closed.

3. If the

oven

door

is opened

and

the

contacts

(COM - NO) of the 1st and 2nd latch switches

fail

to open, the fuse M8A

blows

simultaneously

with

closing

the contacts

(COM -NC)

of the monitor

switch.

CAUTION:

BEFORE REPLACING

A BLOWN

FUSE F

M8A

TEST THE IST

AND

2ND

LATCH

SWITCHES,

MONITOR

SWITCH

AND

MONITOR

RESISTOR

FOR PROPER OP-

ERATION.

MONITOR

RESISTOR

R 0.8 I2 20W

The monitor

resistor

prevents

the fuse M8A

bursting

when the fuse M8A blows due to the operation

of the

monitor

switch.

ASYMMETRIC

RECTIFIER

The asymmetric

rectifier

is a solid

state device

that

prevents

current

flow

in both directions.

And it pre-

vents the temperature

rise of the power transformer

blowing

the fuse M8A when

the high voltage

rectifier

is shorted.

The rated peak reverse voltage of Dl of the asymmetric

rectifier

is 6 KV The rated peak reverse voltage

of D2

of the asymmetric

rectifier

is 1.7 KV. Dl and D2 of the

asymmetric

rectifier or high voltage

rectifier

are shorted

when

the each peak reverse voltage

goes beyond

the

each

rated

peak reverse

voltage.

(The

process

blowing

the fuse M8A.)

1. The high voltage

rectifier

is shorted

by any causes

when microwave

cooking.

2. The peak reverse voltage

of D2 of the rectifier

goes

beyond the rated peak reverse voltage

1.7 KV in the

voltage

doubler

circuit.

6. The fuse M8A blows by the large electric currents.

7. The power

supply

to the all electrical

parts is cut

off.

3. D2 of the rectifier

is shorted.

4. The large electric

currents

flow

through

the high

voltage

winding

of the power transformer.

5. The

large

electric

currents

beyond

6.3A

flow

through

the primary

widing

of the power transfor-

mer.

FUSE

M8A

1. The

fuse

M8A

blows

when

the

contacts

(COM -NO)

of the 1 st latch switch

and 2nd latch

switch

remain closed with the oven door open and

when the monitor

switch

closes.

2. The fuse M8A also blows when asymmetric

rectifier,

H.V.

rectifier,

H.V. wire

harness,

H.V. capacitor,

magnetron

or secondary

winding

of power

trans-

former is shorted.

3. If the wire

harness

or electrical

components

are

short-circuited,

the fuse M8A

blows

to prevent

electric shock of fire hazard.

THERMAL

CUT-OUT

145°C

(MG)

This thermal

cut-out

protects

the magnetron

against

overheat.

If this

temperature

goes

up higher

than

145°C because the fan motor is interrupted,

the venti-

lation

openings

are blocked,

the thermal

cut-out

will

open and the line voltages

to the power

transformer

will

be cut off and the operation

of the magnetron

will

be stopped.

The defective

thermal

cut-out

must be

replaced with

new one.