Nautel XL12, Technical Instructions

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12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 5-4
01 January 2002
(a) Connect a digital multimeter (set to DC volts),
between the anode of CR77 (+) and ground
(TP27) on system control PWB.
(b) If +5
VDC
is present on the anode of CR77, the
internal interlock circuit is open. The probable
cause is an improperly stored ground wand.
(c) If 0.0 VDC is present on the anode of CR77,
the internal interlock circuit is intact. The
probable cause of the alarm is a defective
monitoring circuit. Suspect U27 on the system
control PWB.
5.5.4 B+ POWER SUPPLY - AC FAIL
ALARM:
An AC FAIL alarm on the front panel
indicates a loss of phase or the input AC voltage
falling below 90% of the selected transformer tap
setting. Trouble shoot an AC
FAIL
alarm as follows:
(a) Check the B+ voltage on the transmitter's DC
VOLTS
meter. If it is less than 280 VDC, the
AC power source voltage or main power
transformer tap selection is suspect.
(b) Measure the incoming AC supply voltage and
verify the main power transformer is tapped as
tabulated in table 2-2.
(c) If the transformer taps are correct, the
monitoring circuit is suspect. Contact Nautel
for trouble shooting information.
5.5.5 B+ POWER SUPPLY - OVER
VOLTAGE ALARM:
An
OVER VOLTAGE
alarm indicates that B+ DC voltage applied to the
power modules has risen approximately fifteen
percent above its normal operating level. The alarm
is normally caused by high AC input voltage or
incorrect primary taps on the power transformer.
Trouble shoot a B+ power supply over voltage alarm
as follows:
(a) Check the B+ voltage on the transmitter's DC
VOLTS
meter. If it is greater than 350 VDC,
continue to step (b). If it is less than 350VDC,
go to step (c).
(b) Measure the incoming AC voltage and verify
the power supply transformer is tapped as
tabulated in table 2-2.
(c) If the transformer taps are correct, the
monitoring circuit is suspect. Contact Nautel
for troubleshooting information.
5.5.6 B+ POWER SUPPLY - UNDER
VOLTAGE ALARM:
An
UNDER VOLTAGE
alarm
indicates that B+ voltage has fallen below the B+
threshold level. It is normally caused by low AC
input voltage, use of improper primary taps on the
power transformer, or a faulty rectifier assembly.
Trouble shoot an
UNDER VOLTAGE
alarm as follows:
NOTE
If the
UNDER VOLTAGE
and the AC
FAIL
alarms are
on, it indicates a brown-out.
(a) Check the B+ voltage on the transmitter's DC
VOLTS meter. If less than 275 VDC, continue
to step (b). If greater than 275 VDC, proceed
to step (d).
(b) Measure the incoming AC voltage and verify
the power supply transformer is tapped
correctly as tabulated in table 2-2.
(c) If the AC/DC power supply transformer taps
are correct, switch off AC power and check
3-phase rectifier assemblies.
(d) If the AC/DC power supply transformer taps
are correct and the 3-phase rectifier
assemblies are functional, the monitoring circuit
is suspect. Contact Nautel for trouble shooting
information.
5.5.7 B+ POWER SUPPLY
- TEMPERATURE
ALARM
:
A B+ power supply
TEMPERATURE
alarm
indicates that the charge resistors are getting too hot,
or the charge/ discharge period being monitored by
the power supply monitor PWB is excessive. A high
temperature alarm may be caused by a fault in the
charge contactor's contacts or in the system control
PWB alarm circuitry. Under normal circumstances,
these resistors conduct current for a short period of
time, and do not get hot enough to initiate an alarm.
Trouble shoot a B+ power supply
TEMPERATURE
alarm as follows:
(a) Check B+ voltage on the transmitter's DC
VOLTS
meter. If less than 275 VDC, continue
to step (b). If greater than 275 VDC, go to
step (e).