Theory Of Operation - KitchenAid KHMS105E Service Manual

Microwave Oven Hood Combo Service Manual — LIT 4317216

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 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 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 4
CONTROL
CIRCUIT
2
BOARD
1
1
1-1
L1
(C)
(NO)
(NC)
BASE
THERMAL
FUSE
MICROCOMPUTER
RELAY RY2
RELAY RY4
RELAY RY3
RELAY RY1
RELAY RY5
RELAY RY6
Original 03/97
Page 1-1
BLOWER
(HI)
MOTOR
(LOW)
(C)