Section III. HSS TROUBLESHOOTING
400-Hz power source is used from a bench for the test sei
connect cable W4 between J3 on the test set and the power
source. If the 115-volt, 400-Hz power source in the
helicopter is used, connect cables W4 and W5 in series;
Before removing any HSS LRU, use the
cable W4 connects to J3 on the test set and cable W5
AN/GSM-249 fire control subsystem test set to
connects to the helicopter power source.
perform an HSS subsystem test (paragraph
4-14) with the HSS mounted in the helicopter.
4-14. HSS Troubleshooting Procedures.
a. This section provides direct and general support
troubleshooting procedures for the HSS by using the
AN/GSM-249 fire control subsystem test set. Readings and
procedures differ in some cases between XM128 items and
Procedures for checking out XM128 and
XM136 items. Specific details on differing procedures and
XM136 are identical, but multimeter readings
readings are given in the applicable paragraphs (paragraphs
differ between models in some steps in the test
4-14, 4-20, 4-23, and 4-26.1); where no difference is
table. Determine which HSS model is being
stipulated, the procedures and readings for XM128 items
tested from figures B-1 and B-10, foldouts FO-4
and XM136 items are identical.
and FO-5, and the identification plate on the
EIA. (The only difference in the two models is
b. The tests can be performed on the bench or in the
the differing EIA.)
helicopter with the HSS line replaceable units (LRUs)
electrically isolated from the helicopter. Each step in the
a. After the test-set preliminary procedures in paragraph
tables for HSS and HSS LRU troubleshooting provides
4-13 have been performed, connect the HSS, with the
suggested corrective actions if abnormal indications are
exception of the helmet sight assemblies, as shown in figure
seen. For the troubleshooting of some printed circuit cards,
adjustment procedures are provided. Where no adjustments
are provided, the card should be considered defective and
should be replaced. The "Point of test" column in each
troubleshooting table tells where external test leads are to
When a test is performed on a bench, the
be connected. Where external connections are not
linkage assemblies must be placed on a level
necessary, the column indicates the pin numbers that are
surface with the mounting brackets and rails
being monitored on the unit under test. When repair
also leveled. With the LOD locked in 0-degree
procedures are necessary, refer to the proper section of
position, use the LOD bubble and adjust the
Chapter 5 and disassemble and repair the assembly as
swivel pad, if necessary. This insures that the
rails are not twisted.
4-13. Test-Set Preliminary Procedures.
b. Place the steel fasteners on the arms of the linkage
assemblies in the BIT positions.
c. Set the POWER switch to ON-60 HZ if a 60-Hz
Refer to TM 9-4931-363-14&KP for test-set
power source is used or to ON-400 HZ if a 400-Hz power
source is used.
a. Set all switches with an off position to off (fig. 4-8).
d. Set the multimeter range switch to 10 and the
b. If a 115-volt, 60-Hz power source is used from a
function switch to AC V.
bench for the test set, connect cable W3 between J3 on the
test set and the power source (fig. 4-9). If a 115-volt,
e. Perform the procedures in table 4-2.