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Microwave Oven Hood Combo Service Manual — LIT 4317216
Page 1-1
1-1
Original 03/97
THEORY OF OPERATION
The microwave oven is powered by the 120-
volt line. Whenever the door is closed and a
cooking function is programmed through the
control panel’s keypad, relay contacts on the
control board close, and complete a circuit
from the L1 side to the neutral side of the line.
The control board uses six relays to operate
the various functions of the microwave oven
(shown below). The relays are controlled by
the microcomputer on the control board, and
perform the functions shown below.
Relay 4 controls the speed of the blower motor
through the control panel. The base thermal
fuse will also turn the blower motor on to its
low speed if the temperature reaches 133˚F.
The schematic configuration for relay 4 is
shown in the following diagram. The relay is
explained in further detail on the following
page.
Relay 1 ........................................................ Oven Light/Fan & Turntable Motors
Relay 2 ........................................................ High Voltage Section
Relay 3 ........................................................ Low-Speed Blower Motor
Relay 4 (N.C. Contacts) ........................... Auto Low-Speed Blower Motor
Relay 4 (N.O. Contacts) ........................... High-Speed Blower Motor
Relay 5 ........................................................ Cooktop Lights
Relay 6 ........................................................ Night Lights
RELAY 4
BASE
THERMAL
FUSE
(LOW)
(HI)
(C)
(C)
(NC)
(NO)
BLOWER
MOTOR
L1
1
2
1
CN3
RELAY RY2
MICROCOMPUTER
RELAY RY4
RELAY RY3
RELAY RY1
RELAY RY5
RELAY RY6
CONTROL
CIRCUIT
BOARD