Sharp R-930CS Service Manual page 13

is firmly closed thereby activating both interlock switches. The
primary interlock system consists of the door sensing switch
and primary interlock relay located on the control circuit board.
LATCH
HEADS
DOOR OPEN DOOR OPEN
BUTTON BUTTON
Figure D-1. Door sensing switch, monitor switch and
secondary interlock switches
MONITOR SWITCH
The monitor switch is mounted on the middle position of latch
hook. It is activated (the contacts opened) by the lower latch
head while the door is closed. The switch is intended to render
the oven inoperative by means of blowing the monitor fuse
when the contacts of the primary interlock relay and second-
ary interlock switch fail to open when the door is opened.
Functions:
1. When the door is opened, the monitor switch contact
close (to the ON condition) due to their being normally
closed. At this time the door sensing and secondary
interlock switches are in the OFF condition (contacts
open) due to their being normally open contact switches.
2. As the door goes to a closed position, the monitor switch
contacts are first opened and then the door sensing switch
and the secondary interlock switch contacts close. (On
opening the door, each of these switches operate inversely.)
3. If the door is opened, and the primary interlock relay and
secondary interlock switch contacts fail to open, the
monitor fuse blows simultaneously with closing of the
monitor switch contacts.
CAUTION: BEFORE REPLACING A BLOWN MONITOR
FUSE TEST THE DOOR SENSING SWITCH,
PRIMARY INTERLOCK RELAY, SECONDARY
INTERLOCK SWITCH AND MONITOR
SWITCH FOR PROPER OPERATION. (RE-
FER TO CHAPTER "TEST PROCEDURE").
NOTE: MONITOR FUSE AND MONITOR SWITCH ARE
REPLACED AS AN ASSEMBLY.
THERMISTOR
The thermistor is a negative temperature coefficient type.
The temperature in the oven cavity is detected through the
resistance of the thermistor, and then the control unit
causes the heater relay to operate, thus the current to the
heating element is turned ON/OFF.
MAGNETRON TEMPERATURE FUSE.
The temperature fuse located on the waveguide is designed
to prevent damage to the magnetron if an over heated
LATCH HOOK
DOOR SENSING
SWITCH
MONITOR FUSE
MONITOR SWITCH
SECONDARY
INTERLOCK SWITCH
SWITCH LEVER
OPEN LEVER
11
condition develops in the magnetron due to cooling fan
failure, obstructed air guide, dirty or blocked air intake, etc.
Under normal operation, the temperature fuse remains
closed. However, when abnormally high temperatures are
reached within the magnetron, the temperature fuse will
open at 302˚F(150˚C) causing the oven to shut down.
CONV. THERMAL CUT-OUT
The thermal cut-out located on the left side of the thermal
protection plate (left) is designed to prevent damage to the
heater unit if an over heated condition develops in the heat-
ing unit due to convection fan failure, thermistor failure,
obstructed air ducts, dirty or blocked air intake, etc. Under
normal operation, the thermal cut-out remains closed. How-
ever, when abnormally high temperatures are reached within
the heater unit, the thermal cut-out will open at 302˚F(150˚C)
causing the oven to shut down. When the thermal cut-out has
cooled, the thermal cut-out closes at 266˚F(130˚C).
HEATING ELEMENT
The heating element is located at the left side 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 heating element.
CONVECTION COOKING SYSTEM
This oven is designed with a hot air heating system where food
is not directly heated by the heating element, but is heated by
forced circulation of the hot air produced by the heating
element. The air heated by the heating element is circulated
through the convection passage provided on the outer casing
of the oven cavity by means of the convection fan which is
driven by the convection motor. It then enters the inside of the
oven through the vent holes provided on the left side of the
oven. Next, the hot air heats the food on the turntable and
leaves the oven cavity through the vent in the center of the
oven cavity left side wall. Without leaving the oven, this hot air
is reheated by the heating element, passes through the
convection passage and enters the inside of the oven cavity
again, in a continuing cycle. In this way, the hot air circulates
inside the oven cavity to raise its temperature and, at the same
time, comes into contact with the food being cooked. When the
temperature inside the oven cavity reaches the selected
temperature, the heating element is de-energized. When the
temperature inside the oven cavity drops below the selected
temperature, the heating element is energized again. In this
way, the inside of the oven cavity is maintained at approxi-
mately the selected temperature. When the convection time
reaches 0, the heating element is de-energized and the
convection fan stops operating and the oven shuts off.
DAMPER OPEN-CLOSE MECHANISM
Usually, the damper is in the open position except during
convection cooking. Damper position is set automatically
by damper motor, damper switch, motor cam and damper
shaft. These components are operated by a signal that
judges if microwave cooking or convection cooking opera-
tion is selected by the control unit.
Microwave Cooking:
Damper is in the open position, because a portion of cooling
R-930CS