TM 1-1520-238-10
Change 4
4-14.1/(4-14.2 blank)
of symbols on the video displays. With the EGI modifica-
tion, additional RT’s are connected to the MUX bus. The
DTU and EGI are new LRUs on the aircraft, and they are
connected directly to the MUX bus. The CDU and DNS
SDCC are already installed on the aircraft, but are now
connected to the MUX bus via data bus switches (DBS)
that are normally de–energized. The DBSs energize when
the BBC takes control of the MUX bus, either manually via
the MUX PRI/SEC switch on the CPG FCP or automati-
cally when the FCC indicates a failure to the BBC. The
data bus consists of two identical bus networks separated
down each side of the helicopter and interconnected in
such a manner that loss of data communications is mini-
mized or avoided in the event of battle damage. The multi-
plex bus system receives 115 vac power from the No. 1
essential bus and 28 vdc power from the No. 3 essential
dc bus. The MRTUs are protected by their own circuit
breakers: the DASE by the ASE/AC and ASE/DC circuit
breakers located on the pilot overhead circuit breaker
panel; the symbol generator by the SYM GEN circuit
breaker located on the pilot overhead circuit breaker pan-
el; the remote Hellfire electronics unit by the MSL/ DC
ELEC circuit breaker located on the CPG circuit breaker
panel. The remaining MRTU circuit breakers are located
on the CPG circuit breaker panel and are labeled MUX/ L
PYL OUTBD, MUX/L PYL INBD, MUX/ R PYL OUTBD,
MUX/R PYL INBD, MUX/FAB L and MUX/FAB R. With
the EGI modification, the DTU and EGI have dedicated
circuit breakers on the pilots forward circuit breaker panel.
The CDU circuit breaker is located on the CPG circuit
breaker panel, and the DNS circuit breaker is located on
the pilots forward circuit breaker panel. The status of the
multiplex bus subsystem is continuously monitored by FD/
LS; the on command test (test 08-MUX) will fault isolate to
the specific LRU
or LRU and LRU bus failure
/
. With –45 software the RHE and symbol generator
MRTU functions are tested as part of each subsystem
overall on command test (tests 07-MSL; 13-SYMG)
.
With –49A or –51 software the RHE MRTU functions are
tested as part of the 08 MUX test
/
.
