Nautel NX50, Troubleshooting Manual, Page: 22 / 205

NX50 Troubleshooting Manual Responding to alarms
Page 1-12 Issue 6.0 2019-04-01
Controller: External PDM
Inhibit This alarm occurs if the external PDM inhibit circuit, wired to the
control/interface PWB, is closed. When this alarm occurs, the
transmitter immediately inhibits the PDM and the transmitter's
output power drops to 0 W. The transmitter will automatically
recover when the condition is cleared. Ensure the transmitter is
set to RF Off and disconnect the PDM inhibit circuit from the
transmitter (see
“Controller: External PDM Inhibit” on page 1-43 ).
Measure the impedance of the interlock circuit. If the impedance
measures short circuit (low impedance) the PDM inhibit is closed,
and it will be necessary to locate the external device that is
causing this condition. If the impedance does not measure short
circuit, verify the PDM inhibit circuitry has been properly
configured. If the PDM inhibit circuitry is properly configured and
the alarm persists, replace the control/interface PWB (see
“Control/interface PWB replacement” on page 1-64 ).
Controller: External
Reset This alarm is only visible in the transmitter logs, and indicates the
controller was reset by triggering the controller's reset pin. If this
alarm continues to occur unexpectedly, replace the control/
interface PWB
(see “Control/interface PWB replacement” on
page 1-64 ).
Controller: Fast SWR
Shutback This alarm indicates the peak reflected power measured by the
directional coupler at the output of the transmitter has exceeded
the factory-set threshold. When this alarm occurs, the transmitter
immediately inhibits the PDM and RF drive
(see “
Shutback: ” on
page 1-11 of the Operations & Maintenance Manual). Once the
fault clears, the transmitter will automatically recover, either to the
power setpoint, or to a reduced power as determined by the
cutback routine
(see “
Cutback: ” on page 1-12
of the Operations &
Maintenance Manual). If this alarm occurs in conjunction with the
Exciter's SWR Shutback alarm, it generally indicates a fault in the
transmitter's external RF output network (e.g., rigid-line, antenna,
etc.). If this alarm is occurring while the Exciter's SWR Shutback
alarm is not, verify the wiring between the directional coupler and
the control/interface PWB is not damaged. If not, verify the Fast
SWR Shutback threshold is set properly (contact Nautel to obtain
the correct setting for your transmitter). If this threshold is set
correctly and the alarm persists, replace the control/interface
PWB (see
“Control/interface PWB replacement” on page 1-64 ).
Alarm (with Prefix) Description and Troubleshooting Action