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R990K(W)
CHAPTER 6.
R990K(W)
FUNCTION OF IMPORTANT COMPONENTS
[1] 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 latch head. The latch heads are moved upward and released from
latch hook. Now the door will open.
LAT C H
HE ADS
DOOR OP E N
B UT T ON
Figure D-1. Door Open Mechanism
[2] 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.
[3] 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 blown-
ing the fuse when the contacts of the common and normal open con-
tacts 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. WAs the door goes to a closed position, the monitors witch 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 FUSETEST THE
UPPER LATCH SWITCH, LOWERLATCH SWITCH AND
MONITOR SWITCHFOR PROPER OPERATION. (REFER
TOCHAPTER "TEST PROCEDURE")
LAT C H HOOK
UP P E R LAT C H S WIT C H
S T OP S WIT C H
MONIT OR S WIT C H
LOWE R LAT C H S WIT C H
S WIT C H LE V E R
OP E N LE V E R
6 – 1
Service Manual
[4] THERMAL CUT-OUT 150C (CONV.)
The oven thermal cut-out located on the left side of the thermal protec-
tion plate is designed to prevent damage to the convection heater unit
if an overheated condition develops in the tube due to cooling fan fail-
ure, 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.
[5] THERMAL CUT-OUT 95C (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 operating 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.
[6] TEMPERATURE FUSE 150C (MG)
This fuse protects the magnetron against overheating. If the tempera-
ture 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 trans-
former. The defective fuse must be replaced with new rated one.
[7] FUSE F10A 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.
[8] THERMISTOR
The thermistor is a negative temperature coefficient type.The tempera-
ture in the oven cavity is detected through the resistance of the ther-
mistor, and then the control unit causes the heating element relay to
operate, thus the current to the heating element is turned ON/OFF.
[9] TURNTABLE MOTOR
The turntable motor drives the turntable supporting plate to rotate the
turntable.
[10] CONVECTION MOTOR
The convection motor drives the convection fan and provides the
heated air.
[11] FAN MOTOR
The fan motor drives a blade which draws external cool air.This cool
air is directed through the air vanes surrounding the magnetron and
cools the magnetron. This air is channelled through the oven cavity to
remove steam and vapours given off from the heating foods. It is then
exhausted through the exhausting air vents at the oven cavity.
[12] CONVECTION HEATER
The convection heater is located at the rear of the oven cavity. It is
intended to heat air driven by the convection fan. The heated air is
kept in the oven and force-circulated and reheated by the convection
heater.
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