Thales 421, Эксплуатация и обслуживание, Страница: 173 / 256

LLZ 421
Operation and Maintenance Repair
ILS 420
6−31
Ed. 01.10 SOAC
6.6.3 Replacing Subassemblies
WARNING
The heat sinks of the modulators (MODPA) may warm up during operation. This is normal
and does not affect the function. When replacing these subassemblies it is recommended
to let them cool down for a while or take suitable measures (e.g. gloves).
Take care not to touch the spiky pins of the pin bank close above the lower lever of subas-
semblies LG−A/LG−M and ECU when release this lever to remove it. Danger of injury.
Do not work on parts conducting mains voltage. Switch off mains before.
6.6.3.1 Disconnecting the Voltage before replacing Subassemblies
CAUTION
The voltage must always be disconnected before removing or installing subassemblies
(subject to only a very few exceptions). It is sufficient to switch off the respective transmit-
ter with either of switches TX1 or TX2. The transmitter subassemblies without DC supply
assemblies can also be switched off by means of a PC command. If the LCP or/and the
LVS board must be changed, both TX1
and TX2 must be switched off beforehand.
The VAM and MODEM subassemblies may be removed and installed when live. The spe-
cial design of their contacts prevents damage from occurring.
Before replacing an ACC−module the BCPS must always be disconnected from mains.
6.6.3.2 Remarks to Subassemblies in the Transmitter Rack and Power Supply
The table shown in Fig. 6−7 lists the work which may be necessary after a subassembly has been
replaced. Please also refer to Sections 6.6.1.1 and 6.6.1.1.3 . Regard the following remarks.
− The relevant transmitter must be de−energized before removing or installing subassemblies, pref-
erably by switching it off with TX1/TX2. It should be noted that the following subassemblies are only
de−energized if both power supply switches are switched off: LCP, LVS/DCC−5.
− Several of the subassemblies have DIP−FIX switches or jumpers on their pc boards. It is essential
to check that the switches or jumpers on the new subassemblies are set to the same positions as
on the old subassemblies. Section 6.6.5 contains a list of the DIP−FIX switches and jumpers.
− Subassemblies LG−A and LG−M are assigned to their location for TX1 or TX2. It is not possible
to change LG−A and LG−M between TX1 and TX2 without reloading the associated software.
Subassemblies MODPA in GP only are also not interchangeable without setting of jumper JP5 to
the correct value for location in left (CSB/SBO) or right (CLR/CSB2) position of TX1 or TX2 in GP
active installations.
− To remove a printed circuit board assembly from the transmitter subrack release it with the front
levers of the board if available. Remove it carefully from the subrack. Regard the weight of the
MODPA and the PIN−Diode transfer switch if removing them.
− Inserting the board regard the correct fitting to the guiding bars of the subrack. Press assembly
carefully in the socket on the backpanel. For MODPA some corrections to fit the RF connectors
may be necessary. Take care for correct fitting.
− Check that all the RF cables have been connected correctly before switching the transmitter on
again, and make sure that either the antenna or a dummy load is connected to the transmitter
output signals (CSB and SBO, course and clearance (2F)).
− After a maintenance action which has removed and restored DC power to either transmitter, a sys-
tem reset command should be issued or the ECU should be reset using the ECU reset button.