Service Information - Amana A1200S Service

Magnetron Service Information
Proper Handling of Magnetron Tubes
A magnetron tube must be handled with care. When
handling a tube, always handle by the housing only. Use
caution not to touch or strike the ceramic or metal portion
at the top.
NOTE: The carton used to ship service replacement
tubes is reusable. All inoperative tubes must be
returned to the factory in the carton.
RE220002 Rev. 6
Magnetron Failure Modes
Magnetron failures that have been identified are
generally grouped into the categories shown below:
1. Shorted
a. Air—This is a case where the tube has had the
vacuum envelope destroyed and air has entered
the tube. This will cause internal arcing and high
secondary circuit if high voltage is applied.
b. R.F. Capacitors—May short to chassis. This
condition will also cause loss of high voltage.
2. Open Heater (Filament)—Can be determined by
ohmmeter when the transformer leads are
disconnected. Resistance is normally less than on
OHM; the filament does not short internally. Any tube
removed should be checked since usage tends to
make the filament more fragile. Later handling or
shipping may open the filament and thereby mask the
true failure mode when checked at the factory.
3. Low Power—Caused by "wearout" of emission
characteristics of the directly heated cathode.
Symptoms are: (1) the tube current will take longer
to get to the operating point then a new tube
(normally about 2 - 3 seconds), (2) the tube current
does not get high enough to cause the tube to
oscillate with normal line voltage. The current will be
low, (3) the oven produces low power into a load,
two-thirds or less than normal.
4. Physical Damage—Caused by mishandling of
magnetron tube.
28