(2)
Freighter airplanes, The weather radar R/T units are located below the compartment floor on the centerline in the nose cargo door section. Access is gained through the access door in the compartment floor above the R/T units.
E. When the TEST mode is selected, all parts of the system are energized. In the test mode the following events will initially occur in addition to the special test signal display on the indicator:
EFFECTIVITY
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(1) Gyro pitch signal removed and a synthetic nose-down pitch signal is
supplied to the pitch amplifier.
(2) Gyro signal removed and an artificial roll signal is injected,
simulating a continuously alternating left and right roll.
NOTE:____ The azimuth drive signal, which is always generated,
together with the synthetic pitch and roll signals ensure a
dynamic test on all three antenna axes. These test signals
completely check the stabilization circuitry; however, if a
flight complaint is logged for a deficiency in the
stabilization accuracy, and the test mode indicates no
abnormalities, the gyro inputs should be checked.
(3) Status of fault monitor circuits (except VSWR monitor) is displayed
on the indicator as presence or absence of video test bands.
F. The fault indicators/annunciators, located on the R/T front panel, are designated T/R (or R/T), ANT, and (if provided) VSWR. If a malfunction occurs in a LRU (line replaceable unit), a fault indicator should illuminate (or trip) and the faulty LRU can be determined.
NOTE: When more than one fault lamp comes on at the R/T unit, the R/T
____ should be replaced first since it is more accessible than the antenna. Selecting the alternate system at the weather radar control panel and observing the fault lamps aids isolation of a fault to a specific LRU. See Trouble Shooting Chart.
(1)
Receiver-Transmitter Fault Indicator (T/R or R/T)
(a) If the TR (or R/T) fault indicator is on, it is an indication that there is a failure or out of tolerance condition in the transmitter, receiver, or power supply. It is also an indication of rf leakage or a malfunction of the pitch, tilt, or roll stabilization circuitry.
(2)
VSWR Fault Indicator (if provided)
(a) The VSWR circuit uses an electronic latching type device that will continue to display a warning that sometime since the last check-out a high VSWR condition existed and may still be present. A reset button is included on the front panel.
NOTE: In order to duplicate the condition of a high VSWR
____ caused by the waveguide or antenna it will be necessary to operate the system in the normal (NOR, NORM or NORMAL) mode. Before operating in the normal mode while on the ground, observe the caution and warning notes pertaining to RF radiation from the antenna.
(b) The VSWR lamp is not directly interconnected with the test pattern. However, if the high VSWR condition is still present during ground test it will appear as a periodic break-up in the indicator display and simultaneous flashing of the T/R (or R/T) fault lamp, in addition to latching the VSWR fault lamp.
EFFECTIVITY
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(3) Antenna Fault Lamp (ANT)
(a) Antenna sensors, or mechanical conditions which lead to either sluggish or oscillatory antenna motions can be rapidly detected. If the system is in the TEST mode, video test bands will disappear and the ANT and T/R (or R/T) lamps will illuminate if a fault occurs within azimuth axis rotation and position sensor, tilt axis rotation and position sensor, pitch resolver or roll axis rotation and position sensor.
G. Antenna stabilization faults
NOTE: Stabilization problems may occur as the result of an improperly
____ mounted weather radar antenna. For correct operation, the antenna must be oriented to allow tracking of the INS (vertical) gyro pitch and roll signals within one degree. Alignment of the antenna support assembly is not necessary when simply replacing the antenna because it is accomplished at the time of manufacturing by the use of shims on the antenna support assembly.
2. Prepare for Trouble Shooting____________________________
A. Check that WEA RDR RT1, RT2, IND1, and IND2 circuit breakers on overhead panel P7 are not flagged with Do-Not-Operate identifiers.
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