Troubleshooting Assistance for:

Power module showing both PA FAIL and MOD FAIL alarms in one or more positions.
Transmitter off air, or operating at reduced power, no alarms.
Transmitter off air, no alarms.
Transmitter at 10kW, no alarms on front panel, no indication of active power level.
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.

Transmitter off air, or operating at reduced power, no alarms.

Probable Defect:   Low voltage supply control assembly (power supply cabinet).

Future Preventative Maintenance: Notes:
Failure of this assembly is usually linked to power surges.  Increased surge suppression on the AC line should improve the situation. The low voltage supply control assembly is duplicated in the ND50, however, the supply closest to the control cabinet provide the mod drive enable signal.  If a failure in this assembly takes the transmitter out of service, the assembly from the other supply may be installed, and operation continued at 1\4 power.

Transmitter off air, no alarms.

Probable Defect:  PWM Inhibit being sent.

Future Preventative Maintenance: Notes:
As the PWM inhibit is an external command, usually connected to inhibit rf during antenna system checking, the only thing that can be done for preventative maintenance is regular checks of the external switching circuitry which provides the command. Typically PWM inhibit is end by contactor microswitches to inhibit the transmitter during pattern transfer.  If one of these microswitches fails and forces the transmitter off, switch off the AC mains to the transmitter, ensure that the pattern change contactors are in the desired position, and disconnect the PWM inhibit input from the transmitter’s remote interface pwb.  Note that it would be best to inhibit the pattern change function of the remote control as well, to prevent inadvertent “hot switching” of the transmitter.

Transmitter at 10kW, no alarms on front panel, no indication of active power level.

Probable Defect:  Rf filter fan failure caused selection of emergency power level.

Future Preventative Maintenance: Notes:
Check rf filter fans during regulator maintenance visits, replace if there is evidence of impending failure (such as noisy bearings). The fans on the rf filter are tachometer type, whose output is monitored by a fan fail detector pwb on the interface panel.  If a fan fails, an alarm will appear on this detector, and the control interface pwb to switch to emergency power (10kW, non-adjustable), and a red LED will come on on the pwb (on the rear of the control panel) to indicate the reduced power mode.  Once the fan is replaced, normal operation is resumed by selecting the desired operating level.

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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