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Adjustment Procedures
5-23.
CAPSTAN MOTOR OFFSET CURRENT
ADJUSTMENT.
5-24.
Prior to making the capstan motor offset current
adjustment, verify that the power supply voltages have been
adjusted. Figure 5-3 shows the location of the capstan motor
offset adjustment variable resistor.
5-25.
Connect a suitable dc voltmeter (capable of resolu·
tion to ±5 mv dc) across a 3-ohm resistor (R21 or R22) con·
nected in series with the capstan
motor.
The common side
of the resistance is associated with pin 2 of CJ1 and the high
or motor side is associated with pin 2 of CJ2.
7970B/7970C
5-26.
Load the tape transport and be sure tape is
stopped. Adjust OFFSET control until voltmeter reading is
minimum. An acceptable minimum is any value which is
between +0.100 Vdc and -0.100 Vdc. Typical adjustment
at room ambient temperature
(25°
C) will be in the order
of ±0.080 Vdc.
5-27.
CAPSTAN SERVO FORWARD AND REVERSE
DRIVE SPEED ADJUSTMENTS.
5-28.
Prior to performing the servo forward and reverse
drive speed
adjustment,
ensure that power supply voltages
REVERSE
SYNCHRONOUS
TEST SWITCH
REVERSE
SYNCHRONOUS
ADJUSTMENT
_ _ _ FORWARD
SYNCHRONOUS
TEST SWITCH
---FORWARD
SYNCH RONOUS
ADJUSTMENT
RAMP
ADJUSTMENT
PREAMPLIFIER
TEST PO
I
NT
HIGH SPEED
FORWARD TEST
SWITCH
HIGH SPEED
FORWARD
ADJUSTMENT
HIGH SPEED
REVERSE
ADJUSTMENT
OFFSET
ADJUSTMENT
FWD/
REV
TEST POINT
(BIPOLAR RAMP
GENERATOR)
CAPSTAN SERVO
SPEED SELECTION
PLUG (DIP DUMMY PLUG
)
SHOWN IN
25
TO
45
IPS
POSITION USING CAPSTAN
ASSEM BL Y
07970-60141
TACHOMETER
TEST POINT
7970-518
Figure 5-3. Capstan Servo PC Assembly, Test Points and Adjustments
5-4
Part 2
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