5
Microwave service manual – Model:
microMD UK
Service information
Circuit description
General details
• The low voltage transformer supplies the
necessary voltage to the micom controller
when power cord is plugged in.
• When the door is closed, the primary switch
is ON, the secondary switch is ON, and the
monitor switch opens (contact COM and NO).
When selecting cooking power
level and time
• The micom controller memorizes the
function you set.
• The time you set appears in the display
window.
• Each indicator light turns on to indicate that
the stage has been set.
When touching the start pad
• The coil of the relay is energized by the
micom controller.
• Power input is supplied to the high voltage
transformer through the fuse to the primary
switch and relay 2.
• Turntable rotates.
winding of the high voltage transformer. This
3.2 volts is applied to the magnetron to heat
the magnetron filament through two noise
preventing choke coils.
• A high voltage of approximately 2100 volts AC
is generated in the secondary of the high
voltage transformer which is increased by the
action of the high voltage diode and charging
of the high voltage capacitor.
• The negative 4,000 Volts DC is applied to the
filament of the magnetron.
When the oven is set at any level
except maximum
• The micom controller controls the ON-OFF
time of relay 2 by the applied signal to vary the
average output power of microwave oven as
POWER LEVEL (refer to page
X
).
When the door is opened during
cooking
• Both the primary switch and relay 2 are cut off
primary winding voltage of the high voltage
transformer.
• ON-OFF of relay 2 is coupled electrically with
opening and closing of the secondary switch.
• When the door is opened, the secondary switch
is opened and when the door is closed, the
secondary switch is closed.
• The cooking time stops counting down.
• Relay stops functioning.
• As the door is opened, if the contact of primary
switch and relay 2 and/or secondary switch fails
to open, the fuse opens due to the large current
surge caused by the monitor switch activation,
which in turn stops magnetron oscillation.
L
FUSE
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
SWITCH
N
MONITOR
SWITCH
PRIMARY
• The fan motor rotates and cools the
magnetron by blowing the air (coming from
the intake on the baseplate)
• The air is also directed into the oven to
exhaust the vapour in the oven through the
upper plate.
• Cooking time starts counting down.
• 3.2 volts AC is generated from the filament
MONITOR
SWITCH
L
FUSE
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
PRIMARY
SWITCH
N
TRANS-
FORMER
