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TM 11-6625-646-15
C1
despite phasing differences in SAS
1-26. External Card Test Circuits
amplifier channels, the connections
to  the  yaw  axis  meter  M2  are
1-27. Demodulator-Modulator Card Test Circuit
reversed. For simplicity in text, the
stage is described with the center tap
The demodulator-modulator card test circuit furnishes
of  reference  voltage  transformer
operating voltage, an input signal, and interstage
resistive coupling which simulates a SAS amplifier
T603  connected  to  the  negative
shaping network and connects the output of the
terminal of an axis meter and the
demodulator-modulator card through a gain control
center tap of signal transformer T602
network and an amplifier to loading and metering
connected to the positive terminal.
circuits.
a. Operating Voltage. Twenty-six volts ac from the
a. Twenty-six volts ac from transformer T501 (fig.
power supply of the test set is connected through pin 18
1-2) is connected through pin 19 of the card connector
of DEM/MOD receptacle J70. This 26 volts ac is used
to the primary winding of reference voltage transformer
as reference voltage on all types of demodulator-
T603.
The output of the transformer, 5 volts
modulator cards.
On demodulator-modulator cards
centertapped to the negative side of the axis meter, is
which include a gyro signal amplifier, the 26 volts ac is
applied to a demodulator consisting of diodes CR609
also rectified on the card to furnish dc operating voltage
through CR612 and signal transformer T602. On one
for the amplifier stage.
half-cycle of reference voltage from transformer T603,
b. Input Signal.  Twenty-six volts ac from the
diodes CR611 and CR612 conduct. On the alternate
power supply of the test set is also connected to the
half-cycle, diodes CR609 and CR610 conduct. When a
primary winding of stepdown test signal transformer
diode pair is conductive, the circuit is closed through the
T301 (on card A02V3064). The secondary winding is
associated half of the signal transformer secondary to
center tapped to ground and the opposite ends of the
the positive side of the axis meter.  In effect, the
winding are connected to phase-reversing CARD TEST
positive side of the axis meter is switched from one half
SIGNAL switch S6.  Operating switch S6 to L or R
to the other half of the secondary winding of signal
connects the selected phase of the test signal through
transformer T602 at the power frequency rate. Without
voltage divider R310 and R311 (on card A02V3064) and
an ac signal in the primary winding of transformer T602,
pin 15 of receptacle J67 to the junction of resistors R501
the output to the meter is theoretical zero, a series of
and R503 (on switch S7). The signal is then connected
self-canceling pulses of negligible amplitude which have
through resistors R501 and R503 to pins 8 and 3,
no effect on the axis meter indication.
respectively, of receptacle J70.
b. When a simulated feedback signal from the
c. Shaping  Network  Simulator.
In  normal
amplifier is applied to the primary winding of signal
operation, the demodulator stage is coupled through an
transformer T602, the voltage applied to the meter is the
RC shaping network to the modulator stage (refer to the
signal output of one half of the secondary winding during
applicable SAS maintenance manual).
Since the
its positive or negative half-cycle and the signal output
shaping network is not part of the card circuit, resistor
of  the  other  half  of  the  secondary  during  its
R205 (on card A02V3060) is connected between pins 7
corresponding half-cycle.  The output of the signal
and 1 of receptacle J70 to couple the stages and
transformer at the center tap is a series of positive or
simulate the impedance of the shaping network.
negative pulses, depending upon the phase of the
simulated feedback signal.  This positive or negative
output voltage is applied through calibrating resistor
R648 and contacts 8 and 6 of relay K601 to the positive
side of the axis meter.
8

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