Thales 421, Operation And Maintenance, Page: 166 / 256

LLZ 421
Fault Location Operation and Maintenance
ILS 420
6−24
Ed. 01.10 SOAC
6.5.3.2 Fault on Transmitter Subassemblies
The Fault Location for the transmitter subassemblies requires a correct working monitor system. If the monitor is faulty start with 6.5.3.3. In
the former chapter it is validated that power supplies and LCP are operational and o.k. As reference for further measurement use the PC user
program data recordings made after flight check.
Step Fault A B C
1 a) Aerial Alarm
or
b) StdbyAlarm If a) and not b) go to 2.
If b) and not a) change aerial
and go to 2.
If a) and b) go to B.
Check Transfer Assembly.
If faulty change Transfer As-
sembly, if not go to C. Change Monitor Interface
Board (INTFC).
2 a) Course
Alarm
or
b) Clearance
Alarm If a) and not b) go to 3.
If b) and not a) go to 7.
If a) and b) go to B.
Check and measure Synthe-
sizer Signals.
If signals faulty (frequency)
change Synthesizer, if not go
to C.
Check in dialog Audio
Generator Data against
Reference Data. If devi-
ations change LG−A.
Check antenna system in-
cluding cables from/to.
3 a) CRS Width
Alarm
b) CRS Pos.
Alarm
If a) and not b) go to B,
If b) and not a) go to 4
If a) and b) go to 4
Check CRS SBO measure-
ments of RF Power Amplifier
Data against Reference Data.
If deviations change CRS
MODPA, if not go to C.
Check antenna system in-
cluding cable from/to.
4 a) CRS RF−
Alarm
b) CRS SDM
and/or
DDM
Alarm
If a) and not b) go to B,
If b) and not a) go to 6
If a) and b) go to 6
Check CRS CSB measure-
ments of RF Power Amplifier
Data against Reference Data.
If deviations change CRS
MODPA, if not go to C.
Check antenna system in-
cluding cables from/to.
5 Alarm indica-
tion
"Lower power"
or
"no power" Check VSWR at testpoints
TP1 (CSB path) and
TP2 (SBO path)
at the front of the MODPA’s:
Use an oscilloscope for test-
ing. Hook the probe to either
test point TP1 and TP2.
Verify that a normal detected
waveform appears.
If pulses are seen it indicates a
high VSWR i.e. it is in VSWR
shutdown.
Check PIN diode Transfer
Switch and antenna system in-
cluding cables from/to.
MODPA front view
TP1 (CSB)
TP2 (SBO)
Scope
6 CRS SDM
Alarm
and/or
CRS DDM
Alarm Check in dialog Audio Gener-
ator Data against Reference
Data.
If deviations change LG−A, if
not go to C. Check CRS CSB measure-
ments of RF Power Amplifier
Data against Reference Data.
If deviations change CRS
MODPA, if not go to C.
Check antenna system in-
cluding cables from/to.
7 a) CLR Width
Alarm
b) CLR Pos.
Alarm
If a) and not b) go to B
If b) and not a) go to 8.
If a) and b) go to 8.
Check CLR SBO measure-
ments of RF Power Amplifier
Data against Reference Data.
If deviations change CLR
MODPA, if not go to C.
Check antenna system in-
cluding cables from/to.
8 a) CLR RF−
Alarm
b) CLR SDM
and/or
DDM
Alarm
If a) and not b) go to B.
If b) and not a) go to 9.
If a) and b) go to 9.
Check CLR CSB measure-
ments of RF Power Amplifier
Data against Reference Data.
If deviations change CLR
MODPA, if not go to C.
Check antenna system in-
cluding cables from/to.