Quantcast Operation - TM-9-1270-212-14-P0037


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Figure 1-7. Helmet sight assembly - optical and mechanical parts
TM-9-1270-212-14-P Fire Control Subsystem Helmet Directed XM128 P/N 2277716-00 NSN 1270-00-122-9449 Manual
Simplified Block Analysis
TM 9-1270-212-14&P
linkage steel fastener has been connected to the helmet.
b. Operation. For operation, connector A1P1 is
The lamps in the helmet sight are so wired that they can
connected to the helicopter helmet sight connector in the
be tested in series. The series test bypasses the action dis-
pilot's compartment or the gunner's compartment. Only
connect relays. The three lamps in the sight assembly are
the gunner's connector has wires to pins 7 and 8; therefore,
potted into a single replaceable lamp assembly with unit
the retract-solenoid feature is operative only in the gunner's
designator DS1.
compartment. The solenoid is mechanically operated by
pressing a button on the top of the sight housing; it is
f. Reed Switch. Reed switch S1 in the magnetic
electrically operated in the gunner's compartment as the
receptacle on top of the helmet sight senses the presence of
ACQ TRK STOW switch (refer to figure 2-5) is moved from
the steel fastener on the end of the linkage arm. The reed
ACQ to TRK. Actuating the solenoid allows a spring in the
sight housing to drive the eyepiece counterclockwise to the
switch is open when no fastener is connected and closes
when the fastener contacts the magnet. Proper magnet
horizontal position; the eyepiece must be manually
returned to the vertical position. The spring-loaded solenoid
position in the housing is important for correct operation
engages a detent to hold the eyepiece in its previously set
of the reed switch. White dots on the housing and magnet
must be aligned for the reed switch to sense the presence of
the steel fastener.
c. Eyepiece Adjustment. The eyepiece can be moved up
and down by compressing the spring on the straight shaft,
and the whole sight assembly can be adjusted laterally by
White dots on the housing and magnet may
manually rotating the sight housing. Vertical security is
have to be slightly offset for reed switch to
controlled automatically as the spring contacts the shaft.
sense the presence of the steel fastener.
Lateral security is controlled by the tightness of the screw
inside the helmet that secures the sight housing to the
g. Reticle Lamp Test. The reticle lamps in each helmet
sight are tested by actuating the reticle-lamp test switch on
d. Boresighting. The helmet sight transfers the plane A
the related armament control panel. Actuating this switch
line of sight provided by the reticle in the eyepiece to the
on the pilot or gunner armament control panel energizes a
plane B surface of the four-section magnet in the
relay in the IFCU; this disconnects the ac power and ac
receptacle. Therefore, the vertical and lateral position of
returns from the related helmet sight and applies 15-volt dc
the eyepiece has negligible effect on helmet sight alignment.
power between pins 1 and 4 of the helmet-sight connector.
The alignment  o f these two reference planes is
The series-connected dc power checks for a burned-out
accomplished by adjusting three sockethead setscrews to
lamp (which may not otherwise be detected). Thus, if the
move the magnet in its receptacle. For helmet boresighting,
reticle disappears when the reticle-lamp test switch is
the plane of the magnet is established by the use of the
actuated, one or more of the lamps in the sight is
helmet boresight tool (fig. 2-16), and the two lines of sight
inoperative and the lamp assembly must be replaced. The
are then brought into coincidence by adjusting these
15-volt dc power for the pilot lamp test is supplied from
sockethead screws. Two operators are required for this
dropping resistor R7 on TB1 in the EIA through J1-HH to
adjustment, one to sight through the reticle while the other
the IFCU; 15-volt dc power for the gunner lamp test is
sights through the helmet boresight tool and adjusts the
supplied from dropping resistor R8 on TB1 through J1-GG.
setscrews as required.
e. Power. During normal operation, 0- to 5-volt ac
1-21. Linkage and EIA Theory.
power is provided on pins 1 and 3 of A1P1 from the IFCU
a. General.
through the mating helicopter connector (17P1 or 17P2).
Returns are connected to pins A1P1-2 and -4. This arrange-
ment connects the three lamps in the lamp assembly in
(1) The pilot and gunner linkages operate with part
parallel. However, thc return circuit is provided through
of the EIA circuitry to provide error signals that drive the
the helicopter pilot and gunner action disconnect relays,
TSU or turret servo system into coincidence with the HSS
K83 and K84, when they are energized. These relays are
linkage position. (The remaining EIA circuitry provides the
energized when the reed switch in the helmet sight is closed
BIT capability and is discussed in paragraph 1-22.) The
and deenergized when the reed switch is open. The return
linkages operate with independent but highly similar EIA
circuit for the lamps is complete only when the linkage
circuitry and, thus, for example, the gunner is able to direct
steel fastener (or helmet boresight tool) is connected to the
the TSU with his helmet sight while the pilot directs the
magnetic receptacle. Thus, a reticle is visible only after a
gun turret with his helmet sight.

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