Nautel XL12, Technical Instructions

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12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 5-10
01 January 2002
(c) If the RF output power does not cutback, the
fault no longer exists. Press
ALARM RECALL
.
The fault that caused cutback shall turn red.
Refer to the appropriate paragraph in this
section for trouble shooting information, if
necessary.
5.5.17 RF POWER SHUTBACK ALARM:
An
RF power
SHUTBACK
alarm indicates that the output
power of the transmitter has been reduced to zero.
SHUTBACK
alarm may be caused by a fault in the
transmitter, high VSWR condition, or a fault in the
system control PWB's microprocessor or alarm
circuitry.
NOTE
With the exception of the
MODULATOR
PROTECTION, FAN FAIL
and
BATTERY
alarms, a
SHUTBACK
alarm will accompany the remaining
alarms
.
Alarms that accompany
SHUTBACK
are,
EXTERNAL
PDM INHIBIT
, RF
CURRENT
,
OVER VOLTAGE
,
UNDER
VOLTAGE
,
TEMPERATURE
,
INTERNAL INTLK
,
EXTERNAL
INTLK
and
VSWR
.
The other alarms, such as RF
DRIVE
,
INTERPHASE PDM DRIVE
,
REGULATED
VOLTAGES
and RF
DRIVE AMP
,
shall temporarily
place the transmitter in
SHUTBACK
mode until it
changes from main exciter to standby exciter.
(a) Read the output power from the meter on the
transmitter's control panel. If the output power
is zero, proceed to step (b). If output power is
not reduced, suspect a fault in the system
control PWB's detection/alarm circuitry.
(b) If another alarm lamp is red, refer to the
appropriate paragraph in this manual for trouble
shooting information.
5.5.18 OUTPUT NETWORKS - RF
CURRENT ALARM:
An output networks RF
CURRENT
alarm indicates that excessive RF current
is flowing for too long in the transmitter's output
networks. An RF
CURRENT
alarm may be caused by
a fault in the transmitter that causes too much
current to flow in the output filter, overdriving the
transmitter, a fault in the distribution PWB's
detection circuitry, or a fault in the system control
PWB's alarm circuitry. Trouble shoot an output
network RF current alarm as follows:
(a) Verify the VSWR of the output load does not
exceed 1.2:1 ratio.
NOTE
A
SHUTBACK
alarm will always accompany
an RF
CURRENT
alarm. If an RF current shutback
occurs at least three times within three seconds,
the transmitter shall be in
CUTBACK
mode to
reduce RF output power until the
RF
CURRENT
alarm does not exist.
(b) Press
ALARM RECALL
to verify the
CUTBACK
was caused by an RF
CURRENT
alarm.
Investigate the operating conditions for the time
the alarm occurred. The alarm will trip when
the transmitter is being driven at 13 200 watts
at modulation frequencies below 30Hz.
(c) If the transmitter is not being overdriven,
attempt to clear the alarm by pressing RF
OFF
.
Press and hold
DECR RF PWR
to reduce preset
output to zero.
(d) Press RF
ON
, then press and hold
INCR RF PWR
to gradually raise the output to 12 000 watts. If
the alarm clears, it may have been false.
(e) Measure DC voltage at TP11 on the
distribution PWB. If approximately 0V,
suspect the system control PWB’s alarm
circuitry. If approximately 5V, go to step (f).
(f) Measure DC voltage at the anode of CR2 on
distribution PWB. If it is less than 1.69V and
the transmitter is not being overdriven and no
other fault can be found, suspect a wiring fault
somewhere in the output stages of the
transmitter.
5.5.19 OUTPUT NETWORKS - VSWR
ALARM:
An output networks VSWR alarm
indicates the reflected power is higher than normal.
The
VSWR
alarm trips in two stages. The
VSWR
lamp will turn red when the VSWR reaches 1.35:1,
as a warning to the operator. When the VSWR
reaches 1.5:1, the transmitter will shutback the RF
output power to prevent damage.
An output network
VSWR
alarm can be caused by
excessive reflected power, a fault in the forward/
reflected power probe assembly or a fault in the
system control PWB's alarm circuitry. Trouble shoot
a VSWR alarm as follows: