Sharp Carousel R-990C Service Manual - Page 9

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DOOR OPEN MECHANISM

The door is opened by pushing the open button on the

control panel, refer to the Figure D-1.

When the open button is pushed, the open lever pushes up

the switch lever, and then the switch lever pushes up the

the latch head. The latch heads are moved upward and

released from latch hook. Now the door will open.

LATCH

HEADS

DOOR OPEN

BUTTON

Figure D-1. Door Open Mechanism

UPPER LATCH SWITCH, LOWER LATCH SWITCH

AND STOP SWITCH

1. When the oven door is closed, the contacts (COM-NO)

must be closed.

2. When the oven door is opened, the contacts (COM-

NO) must be opened.

MONITOR SWITCH

The monitor switch is mounted on the latch hook. It is

activated (the contacts opened) by the lower latch head

when the door is closed. The switch is intended to render

the oven inoperative by means of blowning the fuse when

the contacts of the common and normal open contacts of

upper latch switch and lower latch switch

fail to open when the door is opened.

Functions:

1. When the door is opened, the monitor switch contacts

close (to the ON condition) due to their being normally

closed. At this time the common and normal open

contacts of upper latch switch and lower latch switch

are in the OFF condition (contacts open) due to their

being normally open contacts switch.

2. As the door goes to a closed position, the monitor

switch contacts are first opened and then the common

and normal open contacts of upper latch switch close.

(On opening the door, each of these switches operate

inversely.)

3 If the door is opened during cooking, and the common

and normal open contacts of upper latch switch and

lower latch switch fail to open, the fuse blows

simultaneously with closing of the monitor switch

contacts.

CAUTION: BEFORE REPLACING A BLOWN FUSE

TEST THE UPPER LATCH SWITCH, LOWER

LATCH SWITCH AND MONITOR SWITCH

FOR PROPER OPERATION. (REFER TO

CHAPTER "TEST PROCEDURE").

FUNCTION OF IMPORTANT COMPONENTS

LATCH HOOK

UPPER LATCH SWITCH

STOP SWITCH

MONITOR SWITCH

LOWER LATCH SWITCH

SWITCH LEVER

OPEN LEVER

THERMAL CUT-OUT 150˚C (CONV.)

The oven thermal cut-out located on the left side of the

thermal protection plate is designed to prevent damage to

the convection heater unit if an overheated condition

develops in the tube due to cooling fan failure, obstructed

air ducts, dirty or blocked air intake, etc. Under normal

operation, the oven thermal cut-out remains closed. How-

ever, when abnormally high temperatures are reached

within the heater unit, the oven thermal cut-out will open,

causing the oven to shut down. When the oven has cooled

temperature, the oven thermal cut-out closes.

THERMAL CUT-OUT 95˚C (FAN MOTOR)

The thermal cut-out protect the fan motor against over-

heating. If its temperature goes up higher than 95˚C

because the fan motor is locked or the ventilation operat-

ing are blocked, the contacts of the thermal cut-out will

open and switch off the oven. When the thermal cut-out

cools itself down to 75˚C, the contacts of the thermal cut-

out will close again.

TEMPERATURE FUSE 150˚C (MG)

This fuse protects the magnetron against overheating. If

the temperature goes up higher than 150˚C because the

fan motor is interrupted, the air inlet duct is blocked or the

ventilation openings are obstructed, the fuse blows and

cuts off the power supplying to the power transformer. The

defective fuse must be replaced with new rated one.

FUSE M8A 250V

1. If the wire harness or electrical components are short-

circuited, this fuse blows to prevent an electric shock or

fire hazard.

2. The fuse also blows when upper latch switch and lower

latch switch remain closed with the oven door open and

when the monitor switch closes.

3. The fuse M8A also blows when asymmetric rectifier,

H.V. rectifier, H.V. wire harness, H.V. capacitor,

magnetron or secondary winding of power transformer

is shorted.

ASYMMETRIC RECTIFIER

The asymmetric rectifier is a solid state device that pre-

vents current flow ins both directions. And it prevents the

temperature rise of the power transformer by blowing the

fuse M8A when the high voltage rectifier is shorted.

ASYMMETRIC

RECTIFIER

The rated peak reverse voltage of D1 of the asymmetric

rectifier is 6 KV The rated peak reverse voltage of D2 of the

asymmetric rectifier is 1.7 KV. D1 and D2 of the asymmet-

ric rectifier or high voltage rectifier are shorted when the

each peak reverse voltage goes beyond the each rated

peak reverse voltage. (The process of 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

HIGH VOLTAGE

RECTIFIER

R-990C(S)