Section III. THEORY OF OPERATION - TM-9-1270-212-14-P0029

TM 9-1270-212-14&P

Section III. THEORY OF OPERATION

for foldouts (FO-3 through FO-10 and FO-10.1), located at

1-17. General.

the end of the manual.

a. This section provides the mechanical, electrical, and

1-18. HSS and Helicopter Interconnect.

electronic theory of HSS operation. The theory is intended

primarily as a maintenance tool for fault isolation at both

The parts of the HSS are interconnected mechan-

the system and the subsystem levels.

ically and electrically as shown in figure 1-6. The HSS

interfaces with the helicopter by means of three connec-

a. 1. Where XM128 differs from XM136, the differences

tors. A helicopter comector behind the pilot's seat mates

are discussed in this section. If no difference is mentioned,

with J1 on the EIA; this helicopter connector is P261 in the

the two models are identical.

AH1S(Mod) helicopter and 17A1P1 in the AH-lS

helicopter. A helicopter connector at the left of the pilot's

(1) The schematic diagram for the EIA used in

seat mates with helmet sight connector A1P1 for the pilot,

XM128 is foldout FO-4 and the schematic diagram for the

and another helicopter connector at the right of the

EIA used in XMl36 is foldout FO-5; where reference is

gunner's seat, with helmet sight connector A1P1 for the

made to "foldout FO-4 or FO-5," consult the schematic

gunner. In the AH-1S(Mod) helicopter, the connector to

diagram applicable to the EIA in your HSS.

which A1P1 for the pilot mates is P260 and the mating

connector for A1P1 for the gunner is P247; in the

(2) Although the logic card in the EIA used in

AH-1S

helicopter, the pilot's helicopter connec-

XMl28 is designated A10 and the logic card in the EIA

tor is 17P2 and the gunner's, 17P1. The signals carried by

used in XM136 is designated Al5 and separate schematic

the HSS connectors are identified on the detailed

diagrams are provided (foldout FO-7 for card Al0 and

schematics.

foldout FO-10.1 for card Al5), these cards perform the

1-19. HSS Power and Reticle Power.

same functions in the EIA and have identical circuitry in

most areas. Therefore, where a discussion is equally

a. HSS Power. Unregulated 28-volt dc power to operate

applicable to both card Al0 and card Al5, both designators

the HSS is provided from the helicopter through the turret

have been shown, separated by a slash (for example, "card

power circuit breaker and through the MASTER ARM

Al0/Al5" and "XA10/XAl5-5"), and the same method

switch set to STBY to J1-L of the EIA, and 115-volt,

has been used to reference the two schematic diagrams.

400-Hz ac power is provided through the HSS power circuit

(There is no Al5 in the EIA used in XM128 and no A10 in

breaker to J1-J of the EIA. (This control and these circuit

the EIA used in XM136.)

breakers are shown in figures 2-1, 2-6, and 2-7.) Within the

EIA, the 28-volt dc power is distributed to PS1-1, to TB1-6,

b. The HSS contains no operating controls but is

and to XAl0/XAl5-6; and the 115-volt ac power is

operated and tested from controls and indicators mounted

distributed to Ml-1, to T1-1, to T2-5, and to T3-5. Refer to

on the helicopter cockpit panels and is powered by the

foldout FO-4 or FO-.5.

helicopter. HSS cockpit controls and indicators consist of a

brightness control for the reticle in each helmet sight; a test

(1) Power supply module PS1 receives unregulated

switch for testing the lamps that light the reticle in each

28-volt dc helicopter power and converts it to 28-volt dc

helmet sight; a switch that initiates a built-in-test (BIT) of

regulated power for use in the EIA. Refer to foldout F04

the electronic interface assembly (EIA) and pilot and

or FO-5, sheet 2. Components C2, C3, FL1, and FL2 are

gunner linkages; and four indicators that indicate the results

connected to the power supply to allow the EIA to meet

of the BIT.

the electromagnetic interference (EMI) requirements of the

helicopter. The regulated 28-volt output is distributed as

c. The theory discussions are arranged, by function, in

listed for electrical common point 3 (ECP3) on the

the following order: HSS and helicopter interconnect, HSS

schematic.

power and reticle power, helmet sight theory and reticle

lamp test, linkage and EIA theory, and BIT theory.

(2) The items connected to the PSI 28-volt regulated

Appropriate functional diagrams are provided to simplify

output are protected from PSI overvoltage by a crowbar

the presentation. Detailed schematics are located together

circuit located on TB1 (refer to foldout FO-4 or FO-5,

at the end of the section (figs. 1-11 through 1-13) except

1-9