MONITOR (MIDDLE) INTERLOCK
SWITCH
This interlock switch disables the control panel
if the door is open or the catch is out of adjust-
ment or the primary interlock switch fails.
If for some reason the primary switch and sec-
ondary switch stick in the closed position and
the door were to be opened, the circuit would
be shorted through the normally closed safety
switch. This would blow the fuse.
If there appears to be an interlock switch prob-
lem, but the fuse is not blowing, refer to the
Component Test Procedure Section in this
service manual.
NOTE:
IF THE INTERLOCK SWITCHES ARE
REPLACED, THE CATCH MUST BE ADJUST-
ED. SEE DOOR AND INTERLOCK ADJUST-
MENTS SECTION FOR PROPER ADJUST-
MENT PROCEDURE. DEFECTIVE SWITCHES
SHOULD BE DESTROYED TO PREVENT
POSSIBLE FUTURE USE.
IMPORTANT:
IF AT ANY TIME THE OVEN
FUSE BLOWS DUE TO AN OVEN FAULT, OR
THE CIRCUIT BREAKER TRIPS AFTER BEING
RESET ONE TIME WITH THE HOUSE
CIRCUIT UNLOADED EXCEPT FOR THE
OVEN, THE INTERLOCK SWITCHES MUST
BE REPLACED AS A GROUP. THIS IS
BECAUSE THE SHORT CIRCUIT CURRENTS
WILL HAVE DAMAGED THESE IMPORTANT
SWITCHES.
MAGNETRON THERMAL PROTECTOR
The magnetron thermal protector located on
the magnetron is designed to prevent an over-
heated condition in the tube due to fan failure,
obstructed air ducts, etc.
Under normal operating conditions, the thermal
protector remains closed. However, If abnor-
mally high temperatures within the magnetron
approach a critical level, the thermal protector
will interrupt the circuit to the magnetron. When
the magnetron has cooled to a safe operating
temperature, the thermal protector closes and a
cook (or defrost) cycle can be resumed.
HALF-WAVE VOLTAGE DOUBLER CIRCUIT
The half-wave rectification circuit consists of a
diode package and a single capacitor. The
2070
Volts AC from the high voltage secondary wind-
ing is rectified to approximately
4140
Volts DC
(peak voltage) needed for magnetron operation.
1. Diode - a diode is a solid state device that
allows current flow in one direction, but pre-
vents current flow in the opposite direction.
2. Capacitor - a capacitor is able to store elec-
tric energy, as well as pass AC and block DC
current.
WATER TEMPERATURE RISE CHECK
The following procedure should be followed
when low power is suspected in the oven but all
other operations, including cooking light opera-
tion, appear normal.
Power output of the magnetron can be meas-
ured by performing a water temperature rise
check. This test will require a quart glass cup
and an accurate mercury thermometer or ther-
mocouple-type temperature tester. For accu-
rate results the following procedure must be fol-
lowed carefully.
1. Fill a measuring cup with one quart of tap
water and measure temperature of the
water with a thermometer or thermocouple
tester. Stir the temperature probe through
the water until the temperature stabilizes.
Record the temperature of the water and
remove the temperature probe.
2. Place the measuring cup in the oven and put
the oven into the cook (high) cycle for exactly
two (2) minutes. Allow the water to heat.
3. Remove cup from the oven and again meas-
ure temperature making sure to stir the tem-
perature probe through the water until max-
imum temperature is recorded.
4. Subtract the cold water temperature from
the hot water temperature. The result should
be
10
°
C
±
2
°
C
, or between
8
°
C
to
12
°
C
rise
in temperature. If the water temperature is
accurately measured and tested for the
required time period, the test result will indi-
cate if the magnetron tube has low power
output (low rise in water temperature) which
would extend cooking time, or high power
output (high rise in water temperature)
which would reduce cooking time.
Because cooking times can be adjusted to
compensate for power output, the magnetron
tube assembly should be replaced only if the
water temperature rise test indicates a power
output well beyond the normal limits. This test
is only accurate if the power supply line voltage
is
230
Volts while the oven is operating.
ALTERNATE TEST-METRIC
Use same procedure as in preceding para-
graphs except as noted.
1. Use 1000 ML water.
2. Timer for two minutes.
3. Same
4. Water temperature will be between
8
°
C
to
1
2
°
C
higher.
ELECTRICAL OPERATION
By closing the door, the primary and secondary
interlock switches close and monitor switch
opens. The closed switches allow line voltage to
flow through the
10
amp fuse to interlock to
magnetron thermal switch. At this point, line
voltage splits and power is applied to primary
side of high voltage transformer, oven cavity
light, fan motor, and timer.
To complete the circuit, two things must happen
to energize the above Components. The timer
must be set, which will close timer contacts,
and the door must be closed, which activates
the interlock switches. At this time, line voltage
to neutral is applied across high voltage pri-
mary, timer, oven light, and fan.
The
2
3
0 Volt AC input to the primary winding of
the power transformer is converted to approxi-
mately
2070
Volts AC output from the high volt-
age secondary winding. At the same time, the
filament secondary winding of the power trans-
former provides 3.
22
Volts AC to heat the mag-
netron filaments.
The
2070
Volts AC output from the power trans-
former high voltage secondary winding is sent
to a half-wave doubling circuit comprised of a
single diode and capacitor where approximate-
ly
4140
Volts DC (peak voltage) is provided to
the magnetron tube.
The negative
4140
Volts DC applied to the
cathode of the magnetron tube causes the
magnetron to oscillate and produce the 2450
MHz cooking frequency.
The microwave energy produced by the mag-
netron tube is channeled through a waveguide
into the cavity past the diffuser and finally into a
cavity where the load is placed to be heated.
When the timer has completed the selected
cooking time, the timer switch opens. The cir-
cuits are open to the light, timer, fan motor, and
power transformer, and the microwave energy
is no longer produced. Five beeps signal the
end of the cook cycle.
DOOR & INTERLOCK ADJUSTMENTS
DOOR ADJUSTMENTS
The door adjustment on all microwave ovens is
very important to prevent any excessive leak-
age. The microwave leakage levels should be
checked after all door, interlock switches and
associated repairs are made. See the
Microwave Radiation Test Section in this man-
ual for proper testing procedures.
The following door adjustments must be fol-
lowed.
LATCH & CATCH ASSEMBLY ADJUST-
MENTS
CAUTION:
AFTER REMOVING THE CABI-
NET, DISCHARGE THE CAPACITOR BY
PLACING AN INSULATED SCREWDRIVER
ACROSS THE TERMINALS.
To make proper latch and catch assembly
adjustment:
1. Disconnect the power to the unit, remove
the cabinet and discharge the capacitor by
placing an insulated screwdriver across the
terminals.
2. Open the door.
3. Loosen the screws that secure the plastic
interlock bracket until the assembly can
be moved freely back and forth.
4. Hold the door closed securely.
5. Move the plastic catch toward the door until
it stops and door is latched. Next, move the
catch toward the back panel making sure it
is snug against door latch. Check by open-
ing and closing the door. Using an ohmme-
ter, place the leads of the meter across the
terminals of the monitor switch. As the door
is opened, your meter should show a short,
as the door is closed it should show an
open circuit.
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