AT&T Bell System Plant Series Adjustment Procedure page 7

LOOP---
Fig. 5-Measurement of Reei Brake Tension-Typicai
(a) l:sing TP2-35 as the 0-\'olt reference, measure
voltage between TP2-29 and TP2-35. This
will indicate voltage as regulated by potentiometer
R\:l.
( b) l:sing TP2-35 as the 0-\'0lt reference, measure
voltage between TP2-32 and TP2-35. This
will indicate voltage as regulated by potentiometer
R23.
2.07
Capstan Speed and Servo Adjustments:
Tape speed across the magnetic head assembly
is dependent upon the peripheral speed of the
capstan. With tape loaded on the recorder, the
ISS 1, SECTION 034-368-701
capstan shall rotate at 46.3 ±0.5 rpm in both
forward and reverse modes of operation. This
speed corresponds to a tape speed of 5 inches per
second (±1
%).
Preliminary adjustment of servo
controls and checking capstan speed is accomplished
by performing the following procedure.
(1)
Apply power to the recorder and install a
reel of tape, looping the tape around the
head assembly. Do not place the tape around
the capstan. Provide sufficienL Lape within
the vacuum chambers to form proper loop lengths.
(2) Remove power from the recorder.
(3) Using a KS-6854 screwdriver, turn adjustment
screw of potentiometers lRll and 2Rll on
reel servo printed circuit board RSA (Fig. 6)
fully clockwise; then back off six turns
counterclockwise.
(4) Connect patching cords at TP2 as follows:
TP2-14 to TP2-15
TP2-21 to TP2-22
(5) Apply power to the recorder.
(6) Program the recorder for forward operation
and permit the capstan to rotate for a few
seconds.
(7) Program the recorder for stop. In this
mode, the capstan shall not creep.
If the
capstan is creeping, adjust R33 on the capstan
servo printed circuit board CSI\ (Fig. 6) until
the creeping stops.
(8) Carefully grasp the capstan and turn it by
hand gently. The capstan will turn easily
up to a certain velocity, above which rapidly
increasing resistance will be felt due to servo
action. Adjust R33 until the velocity at which
the servo action commences is the same both in
forward and reverse. The capstan servo is then
set up to be in the middle of the dead band
during the standby condition of the recorder.
This completes adjustments preliminary to
measuring the speed of the capstan.
(9) Now finish threading the tape on the transport
by placing the tape around the capstan and
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