BIT failure isolation cont'd

TM 9-1270-212-14&P

eight inputs are high, U6-8 is low, and the low disables

high is connected to U1-5. At U1-5, the high has no

NAND gate U5: that is, a strobe pulse on U5-10 has no

immediate effect but is stored as a buffer-amplifier failure;

effect at U5-8. At counts Q0, Ql, Q6, and Q11, all eight

that is, the testing sequence continues. Assume also that the

gunner linkage is normal. At count Q6 (foldout FO-2), the

inputs are high and, as shown at A9-8 on the diagram, no

enable B pulses are generated. At counts Q2 through Q5

gunner linkage is connected for test. When the relay drive 5

signal energizes K1 on the Al0/Al5 card, it connects U9-6

and Q7 through Q10, one of the eight inputs is low, causing

to U7-13. When the enable A pulse provides the fourth

U6-8 to be high. The high at U5-9 enables U5-10, to cause a

change at U5-8. Thus, when the next four strobe pulses

enable, U9-6 goes low, and this low is connected to U7-13.

appear at U5-10, four negative-going pulses are generated at

U7-11 goes high, causing U7-3 to go low. The low at U7-3

U5-8; these pulses are inverted at U8-6 to become enable B

removes the high from the go latch not input connected

pulses. These pulses are shown at A9-8 on foldout FO-2.

through XA9-25 to A9U3-4. With U3-4 low, U3-6 goes

These four enable B pulses are used to check the four pilot

high; this high is connected through XA9-26 and

buffer amplifiers. If the gunner linkage outputs are

XA10/XA15-24 to U2-3, U2-2, and U1-4. The high has no

abnormal, four additional enable B pulses will be generated

effect at U2-3 and U2-2, but at U1-4, the high causes U1-6

to go low. The high at U3-6 turns on Q6, which energizes

in Iikc manner at counts Q7 through Q10 to test the four

gunner buffer amplifiers.

K5, K5, in turn, provides 28 volts to display an EIA failure.

The system remains inoperative in this condition until

power is momentarily removed to reset the circuitry;

(b) At count Q2, when U10-3 goes low, the low is

however, the BIT switch can be reactuate to repeat the

inverted to a high at U2-12, turning on Q1 to generate a

test as many times as desired without interrupting power.

low at XA9-17. As can be seen on foldout FO-4 or FO-5,

Actuating the BIT switch resets the circuitry, but if the

XA9-17 is connected to relays K1, K2, and K3 in buffer

failure remains, the failure indication will also remain. Note

amplifier A1 through J5-2. The relays energize and connect

that only one buffer-amplifier flip-flop is provided, the U4

the fixed inputs to buffer amplifier A1 and connect the

flip-flop, with inputs at pins 4, 5, 9, and 10. Thus, the

buffer-amplifier outputs to the test resolver, B1. The

circuitry provides the same EIA fail indication if a buffer

rest-resolver outputs (TR2 and TR3) are connected to the

comparator circuits on comparator card A11. The

amplifier fails, whether the buffer amplifier is associated

with the pilot or gunner linkage. This explains why an EIA

comparator outputs (TR2 and TR3 compensated outputs)

failure takes precedence over a linkage failure.

are connected to two inputs of three-input NAND gate

A101A15U9 at pins 12 and 13 through XA10/XA15-33 and

NOTE

-35. The enable B signal is connected to U9-9 and -10. The

enable B signal is also connected to U6-10. The comparator

In the AH-1S(Mod) helicopter, the EIA fail in-

outputs, which enter on XA10/XAl5-35 and -33, are also

dicator is labeled INTFC; in the AH-1S heli-

connected to U6-12 and -13. If both inputs to U6-12 and

this indicator is labeled EIA

copter

-13 are high, the low at U6-11, connected to U6-9, prevents

an enable B signal from affecting the high output at U6-8.

(e) Assume that both linkages are not in their BIT

(c) If buffer amplifier Al is normal and both

brackets at the time BIT in initiated. With a high from U9-6

comparator outputs are high, the enable B signal at

for both linkages and a high at U9-8 for all eight buffer

Al0/Al5U9-9 and -10 causes U9-8 to go low; this low is

amplifiers, the low at U7-8 inhibits the skip logic and also

connected to U5-1. The low at U5-1causes US-3 to go high,

inhibits a GO indication with a low at U2-9. The low at

and the high is connected as one enable to U2-5. The

U7-11 enables the decoder to continue operation. The highs

decoder continues to count, and, when U10-4 goes low, Q1

from all buffer amplifiers provide lows at U5-1 (pilot

cuts off and disconnects buffer amplifier Al, while Q2

b u f f e r - a m p l i f i e r logic) and at U5-13 (gunner

conducts and energizes the relays in buffer amplifier A3.

buffer-amplifier logic). The resulting high at U5-3 provides

The same sequence repeats for amplifier A3 at count Q3.

one enable at U2-5. The high at U5-11 provides one enable

at U2-13. With no buffer-amplifier failures, U4-8 remains

(d) Assume that the pilot linkage failed and that

low and the high at U1-6 provides a second enable at U2-1

one of the four buffer ampliilers is abnormal. When the

and at U2-4. At count Q11 (foldout FO-2), U10-13 on the

defective buffer amplifier is tested, one or both of the

A9 card goes low, causing U3-6 to go high. The high is

inputs at A10/Al5U9-12 and -13 will be low. The enable B

connected through XA9-26 and XA10/XA15-24 to U2-3,

signal will have no effect at U9-8, but the high at U6-11 will

U2-2, and U1-4. The high has no effect at U1-4 but it

enable U6-8 to go low when the enable B signal reaches

provides a third enable at U2-3 and U2-2, U2-6 and U2-12

U6-10. The low at U4-9 causes U4-8 to go high, and this

go low, and the low is inverted at U3-4 and U3-8.

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