(Older Version, with Meters on Power Modules)

 

Troubleshooting Assistance for:

Current Meter on one or more power modules at 1/3 or 2/3 normal level.
Transmitter 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.


Current Meter on one or more power modules at 1/3 or 2/3 normal level.

Probable Defect:  Modulator failure in one of the three PA’s contained in the affected power module.

Future Preventative Maintenance: Notes:
Modulator failures are most commonly linked to power surges or continued operation at high ambient temperatures.  Increased voltage regulation and regular fan filter cleaning will usually help. It is  possible to determine which of the three PA’s is defective while the power module is still installed in the transmitter.  Insert the negative lead of a dc voltmeter through the grill on the front of the module, and measure the voltage from chassis ground to the front lead of the SCR mounted on the front end of each of the three PA’s.  Operating PA’s will show a voltage equal to that on the module test point (nominally 29Vdc), the defective assembly will measure 0Vdc.

Transmitter 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 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 power, 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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