Nautel NX15, Troubleshooting Manual

Page: 28 / 274

NX25/NX15 Troubleshooting Manual Responding to alarms
Page 1-20 Issue 5.0 2016-05-06
Exciter A/B: High
Temperature Foldback This alarm indicates either the average temperature of the 10
hottest power modules in the transmitter has exceeded 80
degrees Celsius, or the rectifier heatsink temperature has
exceeded 80 degrees Celsius, and the transmitter's forward
power is being reduced to maintain temperatures that are below
the above thresholds. Once the high temperature condition has
cleared, it may take up to an hour for the transmitter to return to its
power setpoint, and the alarm will clear when the power is no
longer being reduced. Otherwise, pressing the reset button will
cause the alarm to clear. Check the transmitter’s output network
and verify that the air filter in the back of the cabinet is clean.
Verify the temperature of the transmitter building is within
specifications.
Exciter A/B: Low B+
Voltage This alarm occurs when the B+ voltage measured by the exciter
drops below 75% of the B+ setpoint for more than 10 seconds.
When this alarm is present the exciter will not allow the PDM duty
cycle to be increased to compensate for fluctuations in B+. This
alarm will clear when the B+ voltage measurement exceeds
81.25% of the B+ setpoint. Generally this alarm indicates that the
B+ voltage cannot be increased because the ac voltage is too low.
Check the ac mains voltage connected to the transmitter and
verify the power transformer is tapped correctly.
Exciter A/B: Low
Forward Power 1 (or 2) This alarm occurs when the output power of the transmitter is
below the corresponding user-defined Low Forward Power
Threshold (1 or 2). This alarm should occur with other alarms
indicating why the transmitter’s output power has dropped. See
the troubleshooting information with associated alarms.
Exciter A/B: No B+
Sample This alarm indicates the exciter’s B+ voltage sample is below 40 V
for more than 10 seconds. If there is an associated Low B+
voltage alarm, follow the troubleshooting information for that
alarm. If there are no additional alarms and there is a second
exciter installed, switch exciters and check if the alarm is present
on the other exciter. If the alarm is present on the second exciter,
check the cabling between the B+ sampling point and the control/
interface PWB. If the connection is OK, replace the control/
interface PWB (see
“Control/interface PWB replacement” on
page 1-60 ). If the alarm is not present on the second exciter, or
there is no second exciter in the transmitter, replace the digital AM
exciter PWB (see
“Digital AM exciter PWB replacement” on
page 1-55 ).
Alarm (with Prefix) Description and Troubleshooting Action