Nautel VX150, Manual

Page: 19 / 105

VX150 TO VX2 TROUBLESHOOTING MANUAL RESPONDING TO ALARMS
VERSION 0.1 2020-12-01 PAGE 3.1.11
IPA Output Low This alarm occurs if the pre-amp/IPA PWB's forward power is less than the IPA Output Low
threshold (
70%/14.4 W ). This alarm causes the controller to limit the PA voltage to 30 V .
Check for a +48V Supply Fail alarm and follow the associated troubleshooting procedure if
present. IPA Fail and Pre-amp Fail alarms may also be present. If no associated alarms are
present, turn RF off and run the bias routine in the front panel’s Main Menu -> System
Settings -> Calibration menu. If the alarm persists, enable RF and use a digital multimeter to
measure the voltage between pad B on Pre-amp/IPA PWB (pre-amp bias) and chassis
(ground) and also between pad C on Pre-amp/IPA PWB (IPA bias) and chassis (ground). If the
voltage is less than 1 V at either of these points, suspect the Exciter/Control PWB (A1). If the
voltage is greater than 1 V at both of these points, use a digital multimeter to measure
between pad E (IPA volts) on the Pre-amp IPA PWB and chassis (ground). If the measured
voltage is not within an acceptable range (b43 V and +48 V), with ac power off,
perform a continuity check across F1 of the PS Distribution PWB (A2). If the measurement is
greater than 1 W, replace the fuse (Nautel Part # FA57 in the ancillary kit). If the
measurement is less than 1 W, or replacing the fuse does not clear the alarm, replace the
Pre-amp/IPA PWB (A5) (see “Pre-amp/IPA PWB replacement” on page 1-42). If the voltage
on pad E is acceptable, use a digital multimeter to measure between pad D (pre-amp volts)
on the Pre-amp IPA PWB and chassis (ground). If the measured voltage is not within an
acceptable range (b43 V and +48 V), replace the Pre-amp/IPA PWB (A5) (see “Pre-
amp/IPA PWB replacement” on page 1-42). If the voltage is acceptable, or replacing the pre-
amp/IPA PWB does not clear the alarm condition, suspect the Combiner Interface PWB (A12)
(see “Combiner Interface PWB Replacement” on page 1-50) or the Exciter/Control PWB (A1)
(see “Exciter/Control PWB Replacement” on page 1-46).
Low Forward Power This alarm occurs if the transmitter's average forward power falls below the low forward
power threshold (defaulted to 50% of the preset power level and is user adjustable) due to
PA failures, fan failures, SWR foldback or a pre-amp/IPA failure. The transmitter takes no
action on this alarm. Check for associated alarms, and follow the associated troubleshooting
procedure if present. If no other alarms are being indicated, with RF turned on, use a digital
multimeter to
measure the voltage between pad V and pad W on any PA. If the voltage does
not fall within an acceptable range (between 2.3 V and 3 V), suspect the Exciter/Control PWB
(A1). If the voltage is within this range, perform the “PA resistance checks” on page 1-37,
else suspect the Output Power Probe PWB (A7) (see “Output power probe PWB
replacement” on page 1-45).
Missing Preset This alarm indicates that there are no presets programmed into the transmitter. The user will
not be able to enable RF without first programming a preset.
Modulation Loss This alarm, enabled by the user, indicates that the exciter’s audio modulation level is below
the level specified in the audio loss settings of the active preset (see
“Mod Loss” on
page 3.2.110 of the Operations & Maintenance Manual to enable/disable this alarm and to
configure the resulting action). Depending on the setting, this alarm could trigger a preset
change, inhibit the RF or have no effect (alarm only). Check the appropriate program input(s)
and the mod loss setting for the preset.
Muted Transmitter Output For internal control only; no troubleshooting action required
Alarm Name Description and Troubleshooting Action