Section III. HSS TROUBLESHOOTING

TM 9-1270-212-14&P

Section III. HSS TROUBLESHOOTING

4-12. General.

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

NOTE

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

NOTE

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,

4-9.

adjustment procedures are provided. Where no adjustments

are provided, the card should be considered defective and

NOTE

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

necessary.

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.

NOTE

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

self-test procedures.

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.

4-12