(Newer Version, No Meters on Power Modules)

 

Troubleshooting Assistance for:

Power module showing both PA FAIL and MOD FAIL alarms in one or more positions.
Intermittent MOD FAIL alarms, operation at reduced power.
Tx cutting back with SWR indications, into antenna system AND dummy load or forward/reflected power meter readings are erratic.
ND10 only – INTERLOCK alarm and HIGH TEMPERATURE alarm on internal temperature shutback assembly (NAX69/01).
Transmitter operating at reduced power, one (or more) modules appear to be cutting in and out, audible sound of relay cycling near bottom rear of control cabinet.
Meters are reading erratic & RF Sensitive.


Power module showing both PA FAIL and MOD FAIL alarms in one or more positions.

Probable Defect:  Temperature trip of associated modulator/power amplifier.

Future Preventative Maintenance: Notes:
Regular cleaning of the fan filter on the power module(s) should be part of scheduled maintenance. Adequate airflow is necessary to keep PA operating temperatures within limits.  This will also help to reduce real PA failures.

Intermittent MOD FAIL alarms, operation at reduced power.

Probable Defect:  Loose retaining screw at rear of power module.

Future Preventative Maintenance: Notes:
A check of power module, power supply, and output filter hardware (nuts, bolts, screws) should be made a part of the annual maintenance check. The retaining screw at the rear of the power module forms the main DC return path for the module.  In addition, loose PA output connections on the bottom of the power module can cause arcing of the power module output transformer.

Tx cutting back with SWR indications, into antenna system AND dummy load or forward/reflected power meter readings are erratic.

Probable Defect:  Diodes in forward/reflected power probe, or probe sample transformer arcing.

Future Preventative Maintenance: Notes:
Failures in the power probe are almost always caused by lightning, and are an early warning sign that consideration should be given to improving transmitter site lightning protection.  Nautel’s Customer Service Department can assist with a review of site layout, on request. The diodes in the power probe rectify the forward and reflected power samples to operate the meters and remote power signals.  Therefore, failures of these diodes usually can be seen by indications such as forward power equal to reflected, or a complete loss of forward and/or reflected power readings.

ND10 only – INTERLOCK alarm and HIGH TEMPERATURE alarm on internal temperature shutback assembly (NAX69/01).

Probable Defect:  Defective fan in rf filter, or plugged fan filter.

Future Preventative Maintenance: Notes:
Implement cleaning of rf filter’s fan filter as part of regularly scheduled maintenance. The rf filter fan is located on the bottom of the rf filter, in the front, left hand corner.  Easiest access is by removing the transmitter’s right side panel.  This fan helps to prevent failures of critical filter components, so its proper operation is very important.

Transmitter operating at reduced power, one (or more) modules appear to be cutting in and out, audible sound of relay cycling near bottom rear of control cabinet.

Probable Defect:  40A fuse in power module DC supply line is defective.

Future Preventative Maintenance: Notes:
Loss of these fuses is frequently associated with AC power surges, although it can also be caused by certain power module failure conditions.  Adequate AC line voltage regulation, and sufficient power module airflow (regular fan filter cleaning) should help. If the 40A fuse is blown, the power module will charge through its 3A charge line.  Once the module capacitors are charged, the relay engages to switch in the high current supply.  As the fuse is blown, this causes the 3A line to be loaded down, which makes the relay disengage, and the process begins again, creating the audible clue to the source of the problem.

Meters are reading erratic & RF Sensitive.

Future Preventative Maintenance: Notes:
Wipe the face of the meter with a cloth containing a small amount of dish detergent or antistatic spray.

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