TM11-5895-846-14
The following procedures are divided into functional
(6) If the indication in step (4) above is not
groups since the procedures may be performed
correct, the problem is in the 725 MHz source module
independently.
(7) Check that the power amplifier (PA) is
NOTE
operational and adjusted for the specified output. The
The LNA modules (A1 and A2) are
PA (upconverter) output frequency must be in the range
identical. Prime ac power is applied
of 7975 to 8400 MHz.
directly to each control module and is
(8) Check that the receive path (LNA and
independent of the operation of the unit
downconverter)
is
operational
and
that
the
POWER circuit breaker.
The latter
downconverter is tuned to a frequency which is 725 MHz
control applies ac power to the drawer
power supply module PS1. Module PS1,
(9) Visually check the SHF cable and
in turn, provides dc power to the LNA
connectors from the antenna mounted electronics to the
BITE unit and the transfer switches for
downconverter for damage or loose connections.
LNA standby testing and on-line
(10) If the preceeding tests and checks and the
selection. Also, dc power is applied up
power supply tests are all correct, the problem is in the
to the TRANSLATOR switch.
translator module A3; remove and replace the module
a. Power Supply Tests.
(1) Check that the LNA control/translator
c. LNA Tests. The following procedure will perform
POWER circuit breaker is in the ON position and the
fault isolation for the standby LNA on the antenna. The
POWER indicator is illuminated.
standby LNA must have power applied for at least five
(2) Place the MONITOR switch to each of the
minutes before starting this test.
following positions and observe the MONITOR meter for
(1) Place the power circuit breaker on each
a correct indication at each position.
LNA control panel and on the LNA control/translator to
Position
Indication
the ON position and observe that the associated
+28 V X1
25 to 50
POWER indicators are illuminated. The LNA control
+24 V XI
21 to 27
FAULT indicators should extinguish after the warmup
+ 15 V X0.5
27
period (approximately 5 to 8 minutes), otherwise a valid
-15 V X0.5
27 to 33
fault is indicated.
(3) If any indication in step (2) above is not
(2) Hold the STBY LNA TEST/TEST switch in
correct, the problem is in the power supply module PS1;
the ON position for a minimum of 5 seconds.
(3) Observe that the TEST OSC indicator is
b. Translator Tests.
illuminated.
NOTE
(4) Observe that the LNA NORMAL indicator
A warm-up time of 5 to 8 minutes is
is illuminated.
required to correct operation.
(5) If the indicator in step (4) above is not
(1) Check that the LNA control/translator
illuminated, check the LNA BITE unit adjustment (refer to
TRANSLATOR and POWER circuit breakers are in the
para 5-54). If
the indicator of
step (4) above still does
ON position and that the associated indicators are
not illuminate, the standby LNA is probably faulty (the
illuminated.
associated FAULT indicator may or may not be
(2) Place the MONITOR switch to the 725
LEVEL position and observe the MONITOR meter for an
fault isolation with LNA (LNA maintenance section).
indication of from 15 to 35.
NOTE
(3) If the indication in step (2) above is not
If the standby LNA is not faulty and
correct, the problem is in the 725 MHz source module
you desire to test the operational
LNA, place the ON LINE switch to the
(4) Place the MONITOR switch to the 725 φ
LNA just checked and repeat steps
position and observe the MONITOR meter for an
(2) through (5) above.
onscale steady indication.
5-41. Removal
and
Replacement
of
LNA
(5) If the indication in step (4) above is
wavering (around midrange) the problem may be in the 5
WARNING
MHz input circuit. Check that the BNC connector on
Dangerous voltages exist in the LNA
both ends of the interconnection from the rear of the LNA
control/translator that may cause
control/translator to the 5 MHz source is tight and that
death or injury to personnel even
the 5 MHz source in the upconverter is operational. If 5
when the unit POWER circuit breaker
MHz is present, proceed to step (6) below.
is in the OFF position.
5-64