TM 55-4920-428-13
1-17. ILCA Control Circuits. (See FO-1.)
a. General. The ILCA control circuit includes the command signal circuit, demodulator control cir-
cuit, self and cross demodulators, and servo amplifier.
b. Command signals circuit.
(1) The command signals circuit includes the 0.5 Hz oscillator, the VALVE CONTROL variable
resistor, and wafer B of the FUNCTION SELECT switch. This circuit provides the square wave, closed
loop, hardover retract, balance, or hardover extend command signal to servo amplifier U2.
(2) The oscillator includes nor gates U4A and U4B and associated resistors, capacitor, and diode.
The circuit alternately charges C2 to about 14 volts in each direction for about 1 second. When the
input applied through R10 to gate U4A is -7-volt dc, the output of gate U4A is +7-volt dc. The output
of gate U4B is –7-volt dc. Current from the output of gate U4B flows through C2, R11 and CR3 to the
output of gate U4A. In about 1 second, the voltage at the junction of R11 and C2 increases to about +7-
volts. This voltage, applied through R10, changes the state of gate U4A. The -7-volt dc output from
gate U4A changes the output of gate U4B to +7-volt dc. In about 1 second, the voltage at the junction of
R11 and C2 decreases to about -7-volts. This negative voltage reverses the state of gate U4A and the
cycle repeats. The output of the oscillator is a square wave. Its frequency is 0.35 to 0.65 Hz. Both half
cycles are 6.5 to 7-volts. They are evenly distributed about a O reference. The signal is applied through
the SQ WAVE variable resistor to the FUNCTION SELECT switch at SQ WAVE, the signal is applied
as a command to servo amplifier U2.
(3) The closed-loop command signal is obtained from the moving contact of VALVE CONTROL
variable resistor. When the control is rotated toward RETRACT, the command signal increases toward
+12-volt dc. When the control is rotated toward EXTEND, the signal increases toward -12-volt dc.
When the FUNCTION SELECT switch is at CLSD LOOP, the signal is applied through R58 or R68 as
a command to servo amplifier U2.
(4) The hardover retract and extend command signals are +12-volt and -12-volt dc, respectively.
With the FUNCTION SELECT switch at HARDOVER RETRACT or HARDOVER EXTEND, the
selected signal is applied as a command to U2.
(5) With the FUNCTION SELECT switch at BALANCE, a ground is applied to the input of U2.
c. Demodulator control circuit.
(1) This circuit includes operational amplifier (op-amp) U5D, four
nor gates U1A through U1D,
wafer A of the FUNCTION SELECT switch, and associated resistors. With the FUNCTION SELECT
switch at SQ WAVE, CLSD LOOP, or BALANCE, the output of each nor gate is a square wave. This
square wave controls the associated demodulator. When the FUNCTION SELECT switch is at
HARDOVER EXTEND or HARDOVER RETRACT, the output of each nor gate is a logic low. The
logic low turns off the associated demodulator.
(2) The 13-volt ac reference voltage is applied through voltage divider R20 and R19 to the non-
inverting input of op-amp U5D. The op-amp has infinite gain. The sinewave input produces a square
wave output that is in-phase with the input. The amplitude of the square wave is +7- to -7-volt dc. The
amplitude of the square wave is reduced to +6.4- and -6.4-volt dc by voltage divider R18 and R23. The
reduced square wave is applied to UIA and UIC.
(3) With the FUNCTION SELECT switch at either HARDOVER position, 5-volt dc from the
power supply is applied through the FUNCTION SELECT switch to the four nor gates. The 5-volt dc
drives the nor gates output to -7-volt dc. These logic lows hold the four demodulators at off.
1-17
