Harris DX 25U, Техническое руководство

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L, Modulation Encoder, for additional information and circuit
description to help facilitate troubleshooting an interlock prob-
lem.
NOTE
Place P1 on the DC Regulator in the TEST position and use the
DS1 Bar Graph LED’s on each Modulation Encoder to help
locate the interlock fault. Refer to the Cable Interlock chart on
sheet 4 of the Modulation Encoder schematic, 839-7855-134, in
the Drawing Package. After troubleshooting has been com-
pleted, place P1 in the NORMAL position.
6.25.1
Possible Causes
6.25.1.1
RF Amplifier Module Not In Place
Refer to the DS1 Bar Graph LED display on each Modulation
Encoder to isolate a fault to a group of eight PA Modules.
Remove all AC primary power and open the inner front door
exposing the RF amplifiers. Make sure all PA Modules are
seated properly. Some resistance is normal when inserting and
removing Amps. If all modules are seated, swap one module at
a time with a known good module to isolate the problem to a
particular module. It is possible for a shorted diode on the
module to cause a false Cable Interlock indication.
6.25.1.2 Modulation Encoder Cable Not In Place
Locate the Modulation Encoder ribbon cables on the right side
of the Modulation Encoder. Make sure all are seated properly
with the black “ears” fitting over the connector. Remove all AC
primary power and open the inner front door exposing the RF
amplifiers. The Modulation Encoder ribbon cables connect to
the Combiner/Motherboards with the same type connectors on
the side of the motherboards facing the front of the transmitter.
The appropriate RF amplifier must be removed to allow access
to the ribbon connectors. Check each of these connectors for
proper seating.
6.26
ColorStat™ panel DC Regulator
B+ and B- Supply Faults
If either the DC Regulator B+ or B- Fault LED’s are RED, this
indicates that the supply has failed or a cable is not properly
seated on the board. Refer to SECTION M, DC Regulator, for
additional information.
NOTE
It is sometimes possible for the regulator circuit to lock into a
fault condition if the output of the regulator is accidentally
shorted. If this occurs, turn off the Low Voltage supply at CB1
and CB2 for approximately 1 minute to allow the power supply
to discharge. Reapply Low Voltage and note if the regulator is
now reset.
6.27
ColorStat™ panel Output Monitor
Faults
6.27.1
+5V and -5V Supply Faults
If either of the Output M5V or -5V Fault LED’s on the
ColorStat™ panel are RED, this indicates that the supply has
failed. The transmitter will turn OFF and will not be able to be
turned ON until the fault is cleared. With the Low Voltage on,
measure the voltage on both sides of F1 on the DC Regulator
and verify that it is approxi8 VDC. Measure the voltage
on both sides of F2 and verify that it is approximately -8 VDC.
If a fuse is open, replace the fuse and try again. If the fuse fails
again, troubleshoot the regulator circuit. Refer to SECTION H,
Output Monitor, and SECTION M, DC Regulator, for addi-
tional information.
NOTE
It is sometimes possible for the regulator circuit to lock into a
fault condition if the output of the regulator is accidentally
shorted. If this occurs, turn off the Low Voltage supply at CB1
and CB2 for approximately 1 minute to allow the power supply
to discharge. Turn the Low Voltage back on and note if the
regulator is now reset.
6.27.2
VSWR Faults
6.27.2.1
General Discussion Of VSWR Protection of the
Transmitter
A discussion of VSWR protection is included here to aid the
station technical and engineering staff in determining when
VSWR overloads may indicate a problem that should be located
and corrected. The VSWR protection built into the transmitter
is both for the protection of the transmitter and the protection
of external equipment which might be installed between the
transmitter and the antenna system. Operating at high power
with a VSWR condition can result in high voltages or currents
that can result in arcing, overheating of components, or compo-
nent failure. The VSWR overloads and limits set in the trans-
mitter protection circuitry should not be bypassed or increased
beyond the recommended limits set at the factory.
CAUTION
VSWR OVERLOAD LIMIT SETTINGS THAT EXCEED RECOM-
MENDED VALUES MAY RESULT IN COMPONENT DAMAGE OR
FAILURE.
The transmitter uses two nearly identical circuits to generate a
VSWR fault from two different locations. The Antenna VSWR
monitors the output load of the transmitter. The Bandpass Filter
VSWR circuit detects a VSWR that occurs anywhere in the
transmitter output network and combiner. Should any output
network part fail, the transmitter will be protected.
The Bandpass Filter VSWR circuit will also sense any antenna
load changes, but its sensitivity is set lower. An antenna VSWR
will be detected by the Antenna VSWR circuit first and then by
the Bandpass Filter VSWR circuit.
The first step in VSWR protection is to try to clear the fault.
Most VSWR faults can be cleared by reducing the transmitter
power output to zero for a brief period of time. This zero power
DX-25U
6-14 888-2297-002 Rev. R: 11-11-96
WARNING: Disconnect primary power prior to servicing.