9
DMT2420B
DMT2420R
DMT2420S
DESCRIPTION AND FUNCTION OF COMPONENTS
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 button 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.
Figure D-1. Door Open Mechanism
DOOR SENSING AND SECONDARY INTERLOCK
SWITCHES
The secondary interlock switch is mounted in the lower
position of the latch hook and the door sensing switch in the
secondary interlock system is mounted in the upper position
of the latch hook. They are activated by the latch heads on
the door. When the door is opened, the switches interrupt the
power to all high voltage components. A cook cycle cannot
take place until the door is firmly closed thereby activating
both interlock switches. The secondary interlock system
consists of the door sensing switch and secondary interlock
relay located on the control circuit board.
MONITOR SWITCH
The monitor switch is activated (the contacts opened) by the
latch head on the door while the door is closed. The switch is
intended to render the oven inoperative, by means of blowing
the C/T fuse, when the contacts of the primary interlock relay
(RY2) and secondary 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 primary interlock relay (RY2) and secondary
interlock switch 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 (RY2)
and secondary interlock switch contacts fail to open, the
C/T fuse blows simultaneously with closing of the monitor
switch contacts.
CAUTION: BEFORE REPLACING A BLOWN C/T FUSE
TEST THE DOOR SENSING SWITCH, PRI-
MARY INTERLOCK RELAY (RY2), RELAY
(RY1), SECONDARY INTERLOCK SWITCH AND
MONITOR SWITCH FOR PROPER OPERA-
TION. (REFER TO CHAPTER "TEST PROCE-
DURE").
NOTE: C/T FUSE AND MONITOR SWITCH ARE
REPLACED AS AN ASSEMBLY.
TURNTABLE MOTOR
The turntable motor rotates the turntable located on the
bottom of the oven cavity, so that the foods on the turntable
cook evenly during cooking. The turntable may turn in either
direction.
COOLING FAN MOTOR
The cooling 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 channeled
through the oven cavity to remove steam and vapors given off
from the heating foods. It is then exhausted through the
exhausting air vents at the oven cavity.
CAVITY TEMPERATURE FUSE
The cavity temperature fuse located on the top of the oven
cavity, is designed to prevent damage to the oven by fire. If the
food load is overcooked, by either error in cook time or defect
in the control unit, the cavity temperature fuse will open.
Under normal operation, the cavity temperature fuse remains
closed. However, when abnormally high temperatures are
reached within the oven cavity, the cavity temperature fuse will
open at 302
O
F(150
O
C) causing the oven to shut down.
NOTE: This is fuse. It does not reset.
C/T TEMPERATURE FUSE
The C/T fuse located near the magnetron is designed to prevent
damage to the magnetron if an over heated condition develops
in the tube due to cooling fan failure, obstructed air guide, dirty
or blocked air intake, etc.
Under normal operation, the C/T fuse remains closed. How-
ever, when abnormally high temperatures are reached within
the magnetron, the C/T fuse will open at 302
O
F(150
O
C) causing
the oven to shut down.
1. The C/T fuse blows when the contacts (COM-NO) of the
primary interlock relay (RY2) and secondary interlock
switch remain closed with the oven door open and when
the monitor switch closes.
2. If the wire harness or electrical components are short-
circuited, this monitor fuse blows to prevent an electric
shock or fire hazard.
NOTE: This is fuse. It does not reset.
Door Sensing
Switch
Monitor Switch
Switch Lever
Secondary Interlock
Switch
Latch Heads
Door
