ARMY TM 5-6675-238-14
MARINE CORPS TM 08839A-14/1
is normally operated. The output signals are wrapped
back into the SPU by connecting cable W204 into SPU
test connector J11. Special bit circuitry then checks the
amplitude and phase shift of each signal for roll Xl, roll
X8, heading Xl, heading X32, and pitch Xl. If the
amplitudes and phase shifts are within tolerance, the
loop closer circuitry is considered good. In addition, a
precision amplitude-ratio self-test is performed on the
heading Xl signals, Since the signals do not require any
scaling in the driver circuits, they can be tested without
using precision scaling components for self-test, Several
amplitude-ratio tests are sufficient to assure that the
digital/resolver and digital/synchro circuitry is operat-
ing properly and is within tolerance limits. A no-go on
this test faults the entire digital/resolver and digital/
synchro loop closer circuit. A local reference generator
is used in the SPU to generate 26 VAC, 400 Hz for this
self-test.
(9) Digital/DC loop closer self-test. The digital/
DC loop closer self-test is functionally illustrated in
figure FO-15 and in contained on logic no, 2 electronic
component assembly A2. BITE circuitry for the digital/
DC loop closer self-test are self-test tape to serial data
bus conversion logic, V lamp analog voltage, compare
logic, and voltage check circuit. The tape reader sends
the specific address to activate the digital/DC loop
closer circuits. The tape reader then sends the specific
14-bit digital word that is to be converted to analog,
Since the self-test tape data is made to look like the
computer serial data bus, the self-test exercises the loop
closer circuitry in the same way as it is normally
operated. The output signals are wrapped back to the
SPU by connecting cable W204 into SPU test connector
J11. Special bit circuitry then checks the voltage of
each analog signal and compares it to the expected
value, If all analog signals are within tolerance of the
expected value, the loop closer circuitry is considered
good. During self-test, command D1 signal causes a
relay to energize, thereby connecting the lower gyro
temperature signal to the output of the analog driver.
This is to ensure that the relay is energizing properly.
Command D2 signal energizes the compare logic for
the V lamp signal. A comparison is made of the voltage
on both sides of the relay. If they compare, the overall
digital/DC loop closer circuit is considered operational
and the tape reader is advanced to the next test.
(10) Computer discrete loop closer self-test. The
computer discrete loop closer self-test is functionally
illustrated in figure FO-16 and is contained on logic no.
3 electronic component assembly A3. BITE circuity for
the computer discrete loop closer self-test are self-test
tape to serial data bus conversion logic, SPU internal
discrete voltage generator, and compare logic. The tape
reader sends a specific address to activate the computer
discrete loop closer circuits, When the SELF TEST
switch-indicator is activated, the SPU internal discrete
voltage generator signals are applied to the output
discrete lines. The output discrete signals are listed in
table 6-3. The SPU BITE logic applies the respective
logic 1 signal to each of the output discrete lines. These
lines are then multiplexed and looped back into the
SPU and are checked by the compare logic to see that
all lines are logic 1. For the voltage level checks, the
rated value plus or minus 20 percent is considered to be
a logic 1 condition. Voltages under 20 percent of the
rated value are considered to be a logic 0 condition. If
the logic 1 and 0 comparisons are correct, the computer
discrete loop closer self-test is considered good,
1. SPU Power Supply. The SPU power supply
generates the required dc voltages for operation of the
SPU, tape reader and buffer unit (during self-test), The
power supply is functionally illustrated in figure 6-3.
When the SPU ON switch-indicator is pressed to on,
115 VAC turns on modular power supply PS1, The
+28V generated by modular power supply PS1 ener-
gizes relay Kl, thus applying 115 VAC to modular
power supplies PS2, PS3, and PS4 for turnon. To
prevent damage from an overload condition, the output
of each modular power supply is connected to an
overvoltage protection circuit.
6-4. Buffer Unit Function. The buffer unit is function-
ally illustrated in figure 6-4. The buffer unit performs
two main functions: first, conversion of the bidirectional
single ended data bus from the computer to a bidirec-
tional, differential, high drive capability data bus, suit-
able for transmission over a 10-foot cable to the SPU;
second, synchronization and retiming of various control
signals. The buffer unit performs the conversion of
differential-to-single-ended and vice versa for the con-
trol signals but does not permit control signals to be
bidirectional with the exception of the read/input sig-
nal.
6-5. Tape Reader, Part No. 877406-1, Function. The
tape reader contains the following functional circuits:
lamp assembly, photocell assembly, drive system and
control, step/run control, forward/reverse control, and
power supply, The tape reader is functionally illustrated
in figure 6-5. The following paragraphs describe each
functional circuit.
a. Lamp Assembly . The lamp assembly consists of
~
.
nine special filament-aligned incandescent lamps. These
lamps provide light for the photocells. One lamp is
positioned over each bit position.
b. Photocell Assembly. Data prepunched into the
tape in a single-line, 8-bit character format is read by
conversion of the sensed light energy into electrical
currents. The transmitted light is sensed through the
nine punched holes by light-sensing photovoltiac silicon
cells, The read head consists of nine photovoltaic cells
used as current sinks when illuminated. These cells
provide the input to an associated photocell amplifier
on the photocell amplifier plug-in circuit card. For each
light sensed (hole), the associated amplifier unit input
6-12
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