Troubleshooting Assistance for:

Power module showing both PA FAIL and MOD FAIL alarms in one or more positions.
HIGH or LOW AC alarm. No output.
CUTBACK or SHUTBACK alarms with no indication of reflected power on meter.
Intermittent MOD FAIL alarms, operation at reduced power.
No output, no alarms, DC SUPPLY voltage not normal.
RF DRIVE, LOW AC alarms on startup, operation appears normal.
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. Because ND1 and ND2.5 transmitters require very little cooling, fan filters are often overlooked.  However, adequate airflow is necessary to keep PA operating temperatures within limits.  This will also help to reduce real PA failures.

HIGH or LOW AC alarm.  No output.

Probable Defect:  Transformer tap selection.

Future Preventative Maintenance: Notes:
Ensure transmitter AC circuit is adequate to provide sufficient regulation. To determine if the transformer taps should be changed measure the +24Vdc output of the low voltage power supply.  If it is less than 22Vdc, or more than 26Vdc, a change of transformer taps is in order.

CUTBACK or SHUTBACK alarms with no indication of reflected power on meter.

Probable Defect:  Antenna system does not have sufficient bandwidth.

Future Preventative Maintenance: Notes:
Annual checks of common point impedance.  This should also include a check of impedance at Fc± 10 kHz (the audio sideband limits). If the problem occurs in both the antenna system and into a dummy load, it is possible there is a problem with the power probe in the rf output filter.  The probe must be removed for testing, most commonly, failures occur in the diodes, CR1 through CR4.

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.

No output, no alarms, DC SUPPLY voltage not normal.

Probable Defect:  Low voltage control pwb, or rectifier SCR’s in main power supply.

Future Preventative Maintenance: Notes:
These problems are most commonly associated with power surges.  Best prevention is adequate surge suppression on the transmitter’s AC line. The low voltage supply control pwb (located on the floor of the transmitter, accessible from the rear) contains a 15Vdc regulator (U1) and two PICO type fuses (F1 and F2), which can fail if subjected to a power surge.

RF DRIVE, LOW AC alarms on startup, operation appears normal.

Probable Defect:  Battery on Control Interface pwb.

Future Preventative Maintenance: Notes:
There is a BATT OK indicator on the control interface pwb which should be checked on a monthly basis.  In addition, the battery voltage should be measured once a year. The purpose of the battery is to retain alarm status on loss of AC mains, for troubleshooting purposes.  If the battery is dead, the transmitter sees the OFF command as a loss of AC power, thus the alarms.

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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