Broadcast Electronics FM-5T, User Manual

Page: 162 / 191

2-8
WARNING: DISCONNECT POWER PRIOR TO SERVICING
2-78. Required Equipment. The following equipment is required to adjust the warm-up defeat
time.
A. Wristwatch with seconds hand or stopwatch function.
2-79. Procedure. To adjust the warm-up defeat time, proceed as follows.
2-80. Apply power and operate the transmitter.
2-81. Check the current warm-up defeat time as follows:
1. Depress the FILAMENT OFF switch/indicator to illuminate the switch/indicator.
2. Wait approximately 3 seconds and depress the HIGH VOLTAGE ON
switch/indicator to illuminate the switch/indicator. With the warm-up defeat time
configured at 3 seconds, the filaments will automatically re-energize.
2-82. Refer to Figure 2-1 and select the warm-up defeat feature by operating customer adjust
ment function switch SW1 to position 1.
2-83. Refer to Figure 2-1 and use up/down switch S2 to increase or decrease the warm-up time.
Check the adjustment by repeating the procedure. The control is factory set for 3 seconds.
Each click of S2 is equal to 1 second.
2-84.
FORWARD POWER CALIBRATION.
Potentiometer R83 calibrates the forward power
sample circuit. Adjustment is required only if repairs have been made to the directional
coupler forward port, controller main circuit board, or low-pass filter. To adjust the con
trol, proceed as follows.
2-85. Required Equipment. The following equipment is required to adjust the forward power
calibration control.
A. 1/16 inch jewelers screw-driver, flat-tip.
B. Digital multimeter (Fluke 77 or equivalent).
C. Test load and connecting line (50 Ohm non-inductive, 1 5/8 inch line input, 5 kW
minimum).
D. Calibrated in-line wattmeter with 1 5/8 inch sampling section and cables (Bird
4720 Thruline with 5 kW element or equivalent).
2-86. Procedure. To adjust the control, proceed as follows.
WARNING
WARNING
DISCONNECT ALL TRANSMITTER PRIMARY POWER
BEFORE PROCEEDING.
2-87. Disconnect the transmitter primary power.
2-88. Connect the test load and wattmeter to the transmitter output.
2-89. Connect the multimeter between TP-5 (signal) and TP-1 (ground) or to the chassis.
2-90. Apply power and operate the transmitter in the local manual mode ( REMOTE DISABLE
illuminated, APC ON extinguished) at the desired 100% RF power output as indicated by
the in-line wattmeter.
2-91. Depress the FWD switch/indicator to illuminate the switch/indicator.
2-92. Refer to Figure 2-1 and adjust forward power calibrate control R83 until the multimeter
ind4.25 volts dc.