Nautel XL12, Технические инструкции

Страница: 106 / 238

12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 5-9
01 January 2002
Figure 5-7 Chopper Control Waveform
Audio = 30Hz (AC Coupled)
5.5.14 EXCITER - EXTERNAL PDM
INHIBIT ALARM:
An
EXTERNAL PDM INHIBIT
alarm indicates that an external PDM inhibit
command is present. The alarm could be caused by
an short circuit in the external wiring path to the
remote control PWB, a fault in the switching
circuitry on the remote interface PWB, or a fault in
the alarm circuitry on the system control PWB.
Trouble shoot an
EXTERNAL PDM INHIBIT
alarm as
follows:
(a) If E15 is between pins 2 and 3, verify the DC
voltage at TB1-26 to ground is approximately
+24V on the remote interface PWB.
(b) If E15 is between pins 1 and 2, verify the DC
voltage between TB2-5 and TB2-6 is less than
2.0 VDC.
(c) If the conditions in steps (a) and (b) are met,
measure the voltage across R16 on the remote
interface PWB. If the voltage is +5 VDC, the
remote interface PWB should be repaired.
(d) If the voltage is zero volts, the system control
PWB is suspect.
5.5.15 EXCITER - STANDBY ALARM:
A
STANDBY
alarm indicates that the standby exciter is
operating and that the transmitter has switched from
main exciter to standby exciter. The
STANDBY
alarm
may be caused by a fault in the transmitter that
initiated an automatic exciter changeover or a fault in
the system controller PWB's microprocessor or
alarm circuit. Trouble shoot the
STANDBY alarm as
follows:
(a) Press/hold
ALARM RECALL
and record any
alarm indicators that glow red. Trouble shoot
any recorded alarms to determine the cause of
the exciter changeover.
(b) Assign the active exciter as the main exciter by
momentarily pressing the exciter select switch
that has its indicator glowing. If the
STANDBY
alarm turns green, it was a normal indication of
an automatic exciter changeover.
(c) If the
STANDBY
alarm remains red, suspect a
problem in the alarm circuit on the system
control PWB.
5.5.16 RF POWER CUTBACK ALARM:
An
RF power
CUTBACK
alarm indicates that several
SHUTBACK
alarms (at least three shutbacks in three
seconds) have occurred. A
CUTBACK
alarm may be
triggered by a fault in the transmitter, excessive
VSWR, or a fault in the system control PWB's
microprocessor or alarm circuitry. Trouble shoot a
CUTBACK
alarm as follows:
(a) Read the RF output power level on the
FORWARD POWER
meter on the transmitter's
front panel. If the output power is equal to the
preset operating level, the cutback alarm may
be false. Suspect the system control PWB's
microprocessor or the alarm circuitry. If the
output power is less than the preset operating
level, proceed to step (b).
(b) Momentarily press/release the
DECR RF PWR
switch to clear the cutback alarm and to
restore the preset power level. If the fault
persists, the output power will automatically
cutback again. Observe the front panel and
note which alarm is causing
SHUTBACK
and
CUTBACK
alarms. Refer to the appropriate
trouble shooting paragraph in this section.