LG MS-194A, Service Manual, Page: 45 / 50

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4-4. Microwave generation system_Magnetron (2/2)
* In order to create an electron flow from cathode to anode, the cathode must
be heated and a potential difference must exist between the two.
This is accomplished by heating the cathode with 3, 4 to 3,5 V AC. ( from the
filament winding of the high voltage transformer) and applying a negative
4000 V DC (from the voltage doubler circuit) to the cathode.
* Originally the electrons would travel in a straight line from the cathode to the
anode. However, with the addition of a permanent magnet surrounding the
anode creating a magnetic field, the electrons travel an orbital path between
the cathode and anode. As the electrons approach the anode, their orbital
path takes them past small resonant cavities that are part of the anode.
The passing notion of the electrons induces electron current to oscillate in the
resonant cavities at the very high frequency or 2,450 MHz.
This RF (Radio frequency) energy is then transferred to the antenna.
TESTING MAGNETRON TUBE
* Disconnect power, remove the wrapper, and discharge the capacitor.
* Remove the two leads from the magnetron terminals.
* Connect the ohmmeter between one terminal of the magnetron and the outer case of the magnetron. If the ohmmeter reads
infinity, go to below. If the ohmmeter reads less than infinity, the magnetron is shorted.
* Connect an ohmmeter across the terminals of the magnetron. The ohmmeter should read less than one ohm f the
ohmmeter reads over one ohm or infinity, the tube is defective.
ANTENNA
ELECTRONS
CATHODE
PERMANENT
MAGNET
ANODE
2,450 MHz.