Nautel XL12, Technical Instructions

Page: 104 / 238

12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 5-7
01 January 2002
Figure 5-3 RF Drive Waveform
ƒ
c = 1700kHz (AC Coupled)
NOTE
If the C-QUAM stereo exciter or frequency
synthesizer PWB is being used as the RF drive
source, refer to the associated service instruction
manual for trouble shooting information.
(g) If the RF waveform is present at TP4 and an
alarm is still present, perform the RF
Drive
Tuning
and RF
Drive Level
procedures as
detailed in paragraphs 5.5.21 and 5.5.22.
NOTE
If the C-QUAM stereo exciter or frequency
synthesizer PWB is being used as the RF drive
source, refer to the associated service instruction
manual for trouble shooting information.
5.5.12 EXCITER - INTERPHASE PDM
DRIVER ALARM:
An
INTERPHASE PDM DRIVE
alarm indicates that a fault exists in the interphase
PDM drive signal. It may be caused by a fault on
the interphase PDM driver PWB, the exciter
interface PWB's detection circuitry, or the system
control PWB's alarm circuitry. Trouble shoot an
INTERPHASE PDM DRIVE
alarm as follows:
Figure 5-4 Interphase PDM Waveform
ƒ
pdm = 75kHz (DC Coupled)
(a) The interphase PDM alarm initiates an
automatic exciter changeover to the standby
exciter. To trouble shoot a defective exciter
circuit, set the
Exciter Control
switch A1A3S19
to
AUTO XFR INHIBIT
and select the suspect
exciter.
(b) If the transmitter successfully switched to the
standby exciter, suspect the main exciter's
interphase PDM driver PWB.
(c) Use an oscilloscope to view the signals at J2-1
and J3-1 on the distribution PWB. Each
waveform should be a PDM pulse train, J3-1
delayed by one-half the period. The indications
should be similar to the examples depicted in
figures 5-4 (J2-1) and 5-5 (J3-1). If
waveforms are incorrect, proceed to step (f).
(d) If waveforms in step (c) are satisfactory, use
an oscilloscope to view the waveforms at J4-1
and J4-3 of the exciter interface PWB. If the
waveforms are similar to examples depicted in
figures 5-4 and 5-5, proceed to step (e). If the
waveforms are not satisfactory, proceed to
step (g).