Nautel NX15, Troubleshooting Manual

Page: 37 / 274

NX25/NX15 Troubleshooting Manual Responding to alarms
Issue 5.0 2016-05-06 Page 1-29
Module #:
Overmodulation This alarm indicates the RF power module's PDM Duty Cycle
meter is above 95%. Verify the modulation being applied to the
transmitter is not too high. Try swapping the RF power module
with an RF power module that is not showing this alarm. If the
alarm follows the RF power module, replace the RF power module
(see
“Removing and reinstalling RF power modules” on page 1-
45 ). If the alarm remains with the original position, try replacing
the digital AM exciter PWB (see “Digital AM exciter PWB
replacement” on page 1-55 ) or the control/interface PWB (see
“Control/interface PWB replacement” on page 1-60 ).
Module #: Residual PA
Voltage
Present
This alarm indicates the PA voltage of the RF power module is
higher than expected with either the modulator or the RF amplifier
disabled. See
“Troubleshooting RF power modules” on page 1-48
to determine whether to replace the affected RF power module or
to repair damaged parts, suspecting a failure of one of the FETs.
Module #: RF Drive Fault This alarm indicates that the duty cycle of the RF drive or the dead
time between RF drive signals on the associated RF power
module is not as expected. This alarm causes the RF power
module to be immediately disabled and latched off. Try resetting
the alarm using the AUI. If the alarm persists, try swapping the
affected RF power module with an operational RF power module
in another position. If the fault follows the RF power module,
replace the RF power module (see
“Removing and reinstalling RF
power modules” on page 1-45 ). If the fault remains with that
position, and is also present on an adjacent power module, try
replacing the associated RF Drive cable. If the alarm persists, try
replacing the RF Drive Distribution PWB (see
“RF drive
distribution PWB replacement” on page 1-63 )
.
Rack #: AC Phase Loss This alarm occurs when the SCR rectifier assembly detects a
significant imbalance in the ac phase voltages. The rectifier will
shut down when this condition exists and prevent the transmitter
from generating RF. In a safe manner, measure the voltage of
each phase of the ac mains. If a phase is missing, check the ac
mains fuses. If the ac mains phases are normal and the alarm
persists, check the Phase Loss LED on the rectifier. If it is on,
replace the SCR rectifier (see
“SCR Rectifier Inspection/
Replacement” on page 1-66 ). If the Phase Loss LED is off,
replace the rack interface PWB (see “Rack Interface PWB
replacement” on page 1-64 ).
Alarm (with Prefix) Description and Troubleshooting Action