Nautel XL12, Технические инструкции

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12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 5-11
01 January 2002
NOTE
A
VSWR
alarm will always cause a
SHUTBACK
.
If
the problem occurs three times within three
seconds, the transmitter shall be in
CUTBACK
mode to reduce RF output power until the
VSWR
alarm not exists.
(a) Read the forward and reflected power from
the power meter on the transmitter's control
panel. If the forward power has been reduced
and the reflected power indicates reflected
power, there may be a matching problem
between antenna and transmitter.
(b) Perform a visual inspection of the antenna feed
line and antenna and correct any obvious
problems that can cause excessive reflected
power.
(c) If there are no obvious problems between
transmitter and antenna, measure DC voltage
across C69 on the system control PWB. If
greater than 2.5V, suspect the forward/
reflected power probe. If less than 2.5V,
suspect the system control PWB's detection/
alarm circuitry.
5.5.20 OUTPUT NETWORK -
TEMPERATURE:
An output networks
TEMPERATURE
alarm indicates that the RF output
filter temperature is above 85
°
C. A high
temperature alarm may result from a fault with the
temperature sensing thermistor, temperature detector
sensing circuitry on distribution PWB, or a fault in
the system control PWB. Trouble shoot an output
network
TEMPERATURE
alarm as follows:
(a) Press RF
OFF
, then simultaneously press the
RF power increase and decrease switches to
reduce preset output to zero.
(b) Turn off the AC power at the service
entrance.
(c) Open the rear door. Refer to figure MD-2 to
remove the rear panel of RF output filter A21.
Retain hardware.
(d) Perform a visual inspection of the RF output
filter. Inspect for signs of overheated and/or
defect components or loose connections.
(e) Using ohmmeter, measure the impedance
across thermistor A21RT1. If the reading is
lower than 33K ohms, unplug the MTA
connector mating with J8 of the distribution
PWB (A16).
(f) Repeat impedance measurement of step (e).
If the reading is still lower than 33K ohms,
check the thermistor and the associated wiring.
If the reading is approximately 150K to 200K
ohms (ambient temperature of 25
°
C), suspect
the temperature detector on the distribution
PWB.
(g) Re-install the MTA connector on J8 of the
distribution PWB. Re-install the rear panel of
RF output filter A21. Close the rear door.
(h) Turn on the AC power at the service entrance.
(i) Press RF
ON
and slowly increase the RF
output to 12 000 watts. If the alarm does not
clear, proceed to step (j).
(j) Measure the voltage at TP4 and J5-6 on the
distribution PWB. If approximately 0V,
suspect the system control PWB's alarm
circuitry.
5.5.21 RF DRIVE TUNING PROCEDURE:
The RF drive tuning procedure ensures the series RF
drive tuning components are the correct value for the
transmitter carrier frequency. It also fine tunes the
RF power modules for optimum operation with the
host transmitter. Refer to electrical schematics SD-
3 and SD-9.
5.5.21.1 RF Drive Series Tuning:
The series RF
drive circuit comprises all circuitry between the
connector that mates with E1 on the RF drive
amplifier and the output of the RF drive tuning PWB.
Tune the RF drive series tuning as follows:
(a) Turn off the transmitter and remove AC power
by setting the circuit breaker enclosure circuit
breaker to
OFF
.
(b) Complete the RF drive circuit through relay
assembly A11A7 by moving the push-on
connectors from pin 4 to pin 1 and pin 6 to pin
3.