Nautel FM10, Technical Instructions

Page: 90 / 200

10 000 WATT FM BROADCAST TRANSMITTER
FM10
Page 5-21
01 October 2002
(c) Check for air flow out of the front of the
module and perform a visual inspection for fan
blockage. If a blockage exists, it will be
necessary to remove the RF power module and
clean the obstructed air path or replace the fan,
as required. Verify 24 VDC is present on pin 2
of the connector which normally mates with J8
of the RF power module, to isolate a possible
wiring defect.
(d) Once the RF power module is removed,
measure resistance of temperature sensing
thermistor RT1, located on the top of the
module. If the RF power module has
sufficiently cooled, the resistance should be
near 200 kilohms.
(e) If the resistance reading from step (d) is near
the value specified, the control/monitor PWB's
power module temperature monitor circuitry
may be defective.
NOTE
If it is necessary to check the control/monitor PWB's
power module temperature monitor circuitry, refer
to the control/monitor PWB's service instruction
manual and the trouble shooting data in section 7 of
this manual to isolate circuit defects.
5.11.4 AC PHASE ALARM: An
AC PHASE
alarm can occur due to one or more of the AC input
power phases failing, a wiring fault or defective
components on the low voltage power supply PWB.
If the transmitter RF output has been inhibited, the
fault remains. If the transmitter RF output has been
restored, the alarm was probably caused by a power
fluctuation at the AC power service entrance and
ALARM RESET
should be pressed to clear the alarm
indication. Trouble shoot an AC phase alarm as
follows:
NOTE
An AC phase alarm may cause an
AC PHASE
or a
LOW AC PWR
alarm lamp to turn on. Attempt to
confirm an AC phase alarm by pressing the
ALARM
RESET
switch. If the
LOW AC PWR
alarm lamp
turns off and the
AC PHASE
alarm lamp turns on,
continue trouble shooting. If not, see paragraph
5.11.6.
NOTE
Random alarm occurrences can result from
fluctuations of the AC line voltage at the service
entrance. Monitor the AC line voltage and contact
the power company.
(a) Measure the AC voltage, representative of an
AC phase, between TB1-1 of the low voltage
power supply (A26) and ground. Repeat for
the other two phases on TB1-2 and TB1-3.
(b) If a voltage is not present on one or more of the
terminals measured in step (a), it is probable
that a phase has been lost to the power
transformer's primary. Check the AC power
source.
(c) If a voltage is present on all three terminals
measured in step (a), check fuses F1, F2 and F3
on the low voltage power supply (A26). If the
fuses are not open circuit, suspect a defective
component on the low voltage power supply
PWB or the control/monitor PWB.
NOTE
If it is necessary to check the three-phase monitor
PWB's phase loss monitor circuitry, refer to SD-5
and the trouble shooting data in section 7 of this
manual to isolate circuit defects. If it is necessary
to check the control/monitor PWB refer to the
control/monitor PWB's service instruction manual
and the trouble shooting data in section 7.
5.11.5 HIGH AC PWR ALARM: A
HIGH AC
PWR
alarm can occur if the unregulated 24 VDC,
which is representative of the AC line voltage,
exceeds a pre-set threshold due to AC mains
exceeding the normal level by at least ten percent or
defective components on the control/monitor PWB.
If the transmitter's RF output has been inhibited, the
fault remains. If the transmitter's RF output has been
restored, the alarm was probably caused by a power
fluctuation at the AC power service entrance and
ALARM RESET
should be pressed to clear the alarm
indication. Trouble shoot a high AC power alarm as
follows: