TM 32-5835-005-14& P
f. Captstan Drive System. The Re-
high gain amplifier U1. The resultant
corder/Reproducer uses a dual capstan
square wave is then applied to a four
drive to provide positive control of
input nor gate, U2, where it is trans-
tape motion during adverse environmen-
formed into a series of pulses. The
tal conditions. In recording and re-
resultant pulse train has a constant
producing, the tape leaves the supply
pulse width of 25 S and will vary in
reel (in CASETTE), is fed over a tape
frequency (i.e., the number of "ON"
guide, between the input capstan and
pulses) in direct proportion to the
pinch roller , and past a tape guide to
tach input frequencies. The series of
the take-up reel (in CASSETTE). The
pulses (representing the capstan speed),
stability of the linear speed of the
are applied to the differential ampli-
surfaces of the capstans determines
fier, U3, where they are ccmpared to a
the precision with which the tape is
reference level determined by the speed
moved in the RECORD and REPRODUCE
select. By comparing the capstan speed
modes. For this reason, a servo con-
(voltage level) with a predetermined
trol circuit is used to minimize speed
reference level, an error level is
changes of the capstan drive motor due
produced which in turn compensates the
to variations in torque loading and
speed of the capstan by either increas-
supply voltage. The capstans are belt
ing or decreasing it. By setting the
driven by the servo controlled drive
speed select at either of the variable
motor and the pinch rollers clamp the
speed positions,
1-7/8 IPS or
tape to the capstans in the RECORD and
15/16 IPS, the comparator refer-
REPRODUCE modes. Since the capstan
ence level becomes adjustable and
drive pulleys have slightly different
variable capstan speed of 30% is
diameters, the capstans operate at
achieved.
slightly difference speeds with the
h. Reel Drive System, Search Mode
exit capstan rotating slightly faster
than the input capstan. This differen-
and Take-up Functions. The reel drive
system consists of two motors; the
tial speed produces a controlled ten-
sion in the head area which greatly
take-up motor (A1A1M1) which drives
reduces the possibility of tape-to-
the upper cassette spool and the supply
motor (A1A1M2) which drives the lower
head separation during vibration, shock,
cassette spool. The supply motor is
or acceleration. The motor control
energized by the logic card (A1A6)
board (reference designation AlA5) is
when the REWIND button is pressed.
connected to the SPEED CONTROL on the
This results in the lower spool rotat-
front panel and permits selection of
ing clockwise. The take-up motor,
either 15/16 or 1-7/8 IPS nominal tape
speeds. The combined actions of the
also energized by the logic card, ro-
SPEED VARY and SPEED CONTROL when set
tates the upper spool counter-clockwise
when the FAST FWD button is pressed.
at
15/16 or
1-7/8 IPS permit a
The heart of the logic card is the
+30% speed variation from the nominal
integrated circuit U2 (See Figure 6-5.).
fixed speeds of the unit.
This device called a Quad Latch has
four set-reset flip-flops in a package.
g. Capstan Motor Servo Circuit. (See
It stores the four control commands
Figure 6-4.) Capstan servo contol is
FAST-FWD, REWIND, REPRO and RECORD.
provided by a closed loop, DC refer-
The STOP mode simply resets any or all
enced servo system. Shaft speed infor-
of these four functions and enables
mation is provided by an optical tacho-
brakes. The FAST FWD switch places a
meter. The servo loop consists of the
logic high on the SC input of U2, and
motor AlAlM3, tachometer, A1A1Vl, and
causes a logic high to appear at QC,
the servo control board, A1A5. Voltage
the output of U2. QC then enables the
for the tachometer photo-transistor is
FAST-FWD lamp indicator and take-up
supplied by the servo plug-in card. A
motor; it disables
nearly sinusoidal wave is applied to a
6-5
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