Table of Contents
Advertisement
7. If filament voltage is normal, unplug the
power cord, discharge the capacitor, rein-
stall the high voltage lead and refer to the
Magnetron Filament Test.
PRIMARY
FILAMENT WINDING
(CATHODE)
F
LOW VOLTAGE - 3.35V AC
FA
HIGH CURRENT
HIGH VOLTAGE WINDING CONTINUITY
CHECK - POWER TRANSFORMER
One side of the power transformer high voltage
secondary winding is connected to oven chas-
sis ground. The other end of the high voltage
secondary has one terminal with a red lead.
Since approximately 2070 Volts AC are present
at the high voltage secondary terminal during a
cook (high) cycle, it is not recommended that
the high voltage measurements be attempted.
Normally, a continuity check of high voltage
secondary winding will be sufficient to deter-
mine the condition of the secondary winding.
1. With oven unplugged, discharge the
capacitor and remove the high voltage lead
from the power transformer high voltage
secondary terminal.
2. With an ohmmeter set on the RX1 scale,
measure the resistance between the high
voltage terminal of the power transformer
and oven chassis ground. The reading
should indicate around 80 ohms.
3. If extremely low resistance is indicated, or
if extremely high or infinite resistance is
indicated with the continuity test, replace
the power transformer. A shorted trans-
former will blow the fuse.
MAGNETRON FILAMENT TEST
Disconnect the high voltage leads from the
DIODE
TRANSFORMER
KV
CAPACITOR
magnetron filament terminals. Measure the
resistance across the two magnetron filament
terminals with the ohmmeter set on RX1. If a
normal resistance of less than 1 ohm between
magnetron terminals is indicated on the meter,
make a Power Transformer Test.
If high resistance or infinite resistance is indi-
cated between the magnetron terminals,
replace the magnetron assembly.
DIODE CHECK
1. Set volt ohmmeter to read ohms using
RX10,000 or higher scale.
2. Check resistance between the diode termi-
nals. Reverse leads and check again.
There should be considerable difference
(minimum of 1/2 of scale) between the two
readings, approximately a 10 to 1 ratio. If
reversing the leads does not change the
reading, replace the diode.
The diode may be checked in the unit, but one
lead must be removed. Some high impedance
vacuum tube (V.T.M.) or solid state (F.E.T.)
meters may show an acceptable diode as
defective. These meters will normally show
high ohms (open) in both lead positions.
NOTE:
METERS WITH LESS THAN A 6 OR
TRANSFORMER
9 VOLT BATTERY ARE USUALLY NOT ADE-
QUATE FOR CHECKING THE FRONT-TO-
BACK RESISTANCE OF THE DIODE. THE
METER SHOULD BE CHECKED WITH A
DIODE KNOWN TO BE GOOD BEFORE
JUDGING A DIODE TO BE DEFECTIVE
BECAUSE
READING IN BOTH DIRECTIONS.
If continuity is indicated in both directions, or if
an infinite resistance is read in both directions,
the diode is probably defective and should be
replaced.
If the diode check is normal, go to Magnetron
Check.
CHECKING H.V. DIODES - ALTERNA-
TIVE METHOD
Many times the diode you check as open is
probably good. We have found that many of
you are checking them out on the wrong scale
of your meter, or that your meter is physically
MAGNETRON
not able to check the H.V. diodes we use in our
microwave ovens.
CHASSIS
We are, therefore, providing an alternate test
method for checking diodes in which you do not
need a meter. All you need is a jumper cord and
a 40 watt light bulb.
A simple test set up like this will easily check
H.V. diodes.
The test procedure is:
1. Connect an alligator clip to each terminal of
diode.
2. Plug in cord.
a. If the bulb doesn't light, the diode is open.
DIODE
KV
MAGNETRON
CAPACITOR
CHASSIS
OF AN INFINITE RESISTANCE
40W
6
b. If bulb lights normally both ways when
leads are reversed, diode is shorted.
c. A normal diode will produce a dim light
when the leads are placed on the diode in one
direction.
Before making any checks get a known good
diode and make a test for comparison.
CAPACITOR TESTS
If the capacitor is open, no high voltage is avail-
able to the magnetron. A shorted capacitor nor-
mally causes high line current, which should
trip the wall circuit breaker or blow the line fuse.
An ohmmeter can be used to check for a short-
ed or open capacitor.
1. With an ohmmeter set on the highest scale,
measure the resistance between the two
capacitor terminals. The meter should indi-
cate continuity between the terminals for a
short time and should indicate an open cir-
cuit once the capacitor is charged.
Reversing the meter leads should give the
same indication.
2. If the ohmmeter indicates continuity
between the capacitor terminals at all
times, or if no meter deflection occurs at all,
the capacitor should be replaced.
NOTE:
THE OHMMETER SHOULD BE SET
ON THE HIGHEST RESISTANCE
SCALE WHEN MAKING A CAPACI-
TOR CHECK. CAPACITORS WITH
INTERNAL RESISTOR CAN SHOW
A RESISTANCE AS LOW AS TWO
(2) MEGOHMS.
MAGNETRON THERMAL PROTECTOR
DIODE
TRANSFORMER
KV
CAPACITOR
TEST
Unless an overheat condition exists, a continu-
ity check across the thermal protector contacts
should indicate a closed circuit. The thermal
protector opens at approximately 150-C (302-
F) if used.
DISASSEMBLY & REPLACEMENT OF
PARTS
CABINET REMOVAL
1. Disconnect the power cord from the wall
outlet.
2. Remove the screws from the rear edges of
the case. When replacing screws, make
sure at least one screw has a star washer or
serrated head on it for proper grounding.
3. Slide the cabinet back about one inch.
4. Lift the cabinet from the unit.
MAGNETRON
CHASSIS
Hide quick links:
Advertisement
Table of Contents
