2-92. Opening and then grounding the positive motor line, either SERVO IN A or SERVO IN B, makes
it possible to start the motor in the reverse direction by changing the polarity on the other input signal line,
It also provides a rotor position sense signal, LMAX GND from 1A8A3S1 and LMIN GND from 1A8A3S2,
to the tune control and sequencing circuits, depending upon which limit switch is actuated. The LMAX
GND signal goes to Tune Control PWB Assembly 1A4 (see paragraph 2-1 18). The LMIN GND signal goes
2-94. The servo amplifier has four distinct modes of operation and depends upon control signals from
other circuits of the servo system.
2-95. SERVO DISABLED CONDITION
2-96. When the SERVO ENABLE (ground) signal is not present, pin 8 of 1A5 is at +19.0 Vdc. This causes
the grounding of both servo amplifier output lines (pins 1 and 5 of 1A5) as shown in table 2-2.
SIGNAL AND LOCATION
SERVO IN A (Pi-l)
GND THRU 1A5Q10
SERVO IN B (P 1 -5)
GND THRU 1A5Q14
2-97. This condition is present when the power amplifier is TUNED and READY to operate. Grounding
the servo amplifier outputs prevents activation of servo motor 1A8A3B1 by spurious signals. The SERVO
ENABLE (ground) signal is provided automatically by Tune Control PWB Assembly 1A4, as the TUNE
(ground) signal, when the power amplifier must be retuned.
2-99. At the beginning of the TUNE CYCLE, the polarity of the servo amplifier outputs are such that
the SERVO IN B signal is grounded through transistor 1A5Q14 and the SERVO IN A signal is +19 Vdc
through transistor 1A5Q9, This forces torque motor 1A8A3B1 to tune the coil wiper of 1A8A5L1 toward
the LMAX position. To accomplish this, a positive (about + 10V) LMAX FORCE signal is applied to pin 6
of 1A5 from Tune Control PWB Assembly 1A4. Table 2-3 shows the effect of the positive LMAXFORCE
signal in the servo amplifier.
2-101. At the start of the final tuning cycle (LMAX FORCE cycle completed), the servo amplifier is forced
to turn the rotor of coil 1A8A5L1 toward the minimum inductance (and the correct tune setting) position.
This is necessary because the initial outputs from the phase discriminator are not high enough to control
the servo amplifier. The LMIN FORCE signal (about +10V) from the tune control circuits has the
following effects on the servo amplifier circuits shown in table 2-4.