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HARRIS
888-9058-001
WARNING: Disconnect and lockout AC primary power prior to servicing
200
8.4.3 RF FET Replacement
CAUTION:
THE RF AMPLIFIER FETS ARE SENSITIVE TO DAMAGE FROM STATIC
ELECTRICAL DISCHARGE, AND SHOULD BE HANDLED IN AN ANTI-STATIC
ENVIRONMENT. A GROUNDED WORKING SURFACE, GROUNDED IRON,
AND ELECTROSTATIC DISCHARGE BRACELET SHOULD BE USED.
CAUTION:
IN ORDER TO PROTECT THE NEW FETS FROM ACCIDENTAL DAMAGE TO
OVERCURRENT, BE SURE TO TURN OFF THE BIAS (FULLY COUNTERCLOCKWISE)
TO ALL FOUR FET POSITIONS ON THE QUARTER MODULE
BEFORE INSTALLING THE NEW FETS.
CAUTION:
WHEN CLEANING THE OLD THERMAL COMPOUND FROM UNDERNEATH
THE FET AFTER REMOVAL, USE A SWAB WITH JUST ENOUGH SOLVENT TO
CLEAN THE SURFACE. DO NOT USE TOO MUCH SOLVENT, AND DO NOT
USE AN AEROSOL SPRAY CLEANER, AS EITHER MAY SEEP UNDERNEATH
NEARBY FETS AND DISSOLVE THE THERMAL COMPOUND FROM UNDER
THEM, CAUSING PREMATURE FAILURE.
WARNING:
RF TRANSISTORS, ISOLATION RESISTORS, AND INPUT ATTENUATORS CONTAIN
BERYLLIUM OXIDE (BEO) CERAMIC, A HAZARDOUS MATERIAL. THE LIDS ARE
MADE FROM AL2O3 AND ARE HARMLESS. THE BEO IS HARMLESS WHILE INTACT,
BUT THE DUST IS TOXIC. AVOID CRUSHING OR BREAKING THE BEO CERAMIC,
AND DISPOSE OF FAILED DEVICES PROPERLY.
The Phillips FET (ON4402H) is used for both low band and high band modules. Each
FET is marked with a gain code and a threshold code. For replacement the gain code is
the most important. The quarter module has been assembled in the factory with FETs
that have the same gain code. When the quarter module is aligned the gain is set with an
attenuator on the input. Therefore the FET being replaced must have the same gain code
as the other FETs on the quarter module for proper performance. The gain code is a
number (3 through 7) located above and to the left of the ON4402H marking on the cap.