Service manual

STP 11-25R13-SM-TG
3 - 12
PERFORM PMCS ON A TRANSMITTER
113-575-3053
Conditions: In a tactical or garrison environment, given a transmitter, dual-trace oscilloscope with
frequency counter and 10X test probes, multimeter with test leads, manometer, subminiature plumbing
cap (or other hardware), dummy load, binoculars, electronic equipment tool kit, cleaning cloth, pencil and
paper, DD Form 314, DA Form 2404, DA Form 2407, DA Pam 738-750, Federal Communications
Commission (FCC) and local country modulation (LCM) standards, manufacturers' manuals, and another
person for safety.
Standards: The standards are met when the transmitter is serviced and measurements are in
compliance with prescribed FCC and LCM standards.
Performance Measures Results
WARNING: For safety, always work on transmitters with another person present.
1. Turn OFF transmitter power. P F
2. Check components for excessive heat. P F
a. Clean air filters by rinsing with water and air-drying. P F
b. Check cabinet temperature of the air around all high voltage rectifier tubes. P F
3. Check the pressure in the air handling cooling system of the power amplifier (PA)
stage.
P F
a. Check the condition of all ducts, boots, and blower cages inside the transmitter. P F
NOTE: A unit that has been in operation for a number of years can suffer from reduced air-
system efficiency because of the collection of microdust on the blades and cage of a blower
or along the sides of a discharge duct or boot.
b. Document the backpressure existing within the PA cavity. P F
NOTE: Take readings during periods of calm weather; strong winds can result in erroneous
readings because of pressure or vacuum conditions at the transmitter air intake or exhaust
ports.
(1) Measure with a manometer. P F
(2) Disconnect the manometer and seal the connection point with a subminiature
plumbing cap or other hardware.
P F
CAUTION: Be extremely careful to prevent water in the manometer from back flowing into
the PA compartment. Do not leave the manometer connected to the PA compartment when
the transmitter is on the air.
c. Service transmitter suffering from decreased or increased air pressure in the PA
compartment ASAP.
P F
NOTE: Failure to restore the cooling system to proper operation could lead to premature
failure of the PA tube or other components in the input or output compartments. Decreased
backpressure could indicate a problem with the blower motor or a buildup of dust and dirt on
the blades of the blower assembly. Increased backpressure could indicate dirty PA tube
anode cooling fins or a buildup of dirt on the PA exhaust ducting to the outside.
4. Clean and polish all safety gaps. P F
5. Check door interlocks and safety switches to ensure proper operation. P F
6. Check spare crystal to ensure proper operation in an emergency. P F
7. Connect the sync reference signal, Black Burst, from the sync generator to the
transmitter.
P F
8. Connect a 400 Hz audio signal at 0 dBm from the ATSG to the transmitter. P F