HP 7970B Operating And Service Manual page 29

Adjustment Procedures
c. Adjust the capstan servo PC assembly RAMP con-
trol (See figure 5-3.) to obtain the time listed in table 5-1
for tape unit synchronous speed. Use the vertical gain vernier
control of the oscilloscope to expand the waveform so that
the 90% point may be conveniently measured.
5-6
Note
On HP 180 Oscilloscopes, the vertical spacing is
a special horizontal time scale at 7.2 divisions
which may be used to measure the time at the
90% level.
Table 5-1. Capstan Servo Start/Stop Time
SPEED (IPS) TIME (90%)
12.5 26.1 ms
18.75 17.1ms
22.5 14.1 ms
25
12.6 ms
37.5 8.1 ms
45
6.6 ms
7970B/7970C
5-36. REEL SERVO ADJUSTMENTS.
5-37. Load a short length of tape onto the transport and
bring to load point. The following adjustments determine
the peak deflections of the tension arms. The amount of
deflection desired is a function of the synchronous speed.
At the highest speed (45 ips) the deflection is set so the
tension arms deflect to the outer marks located on the back
side of the casting, both in forward and reverse drive modes.
At lower speeds the amount of deflection is smaller (Le., at
25 ips the deflection is about half (25/45) the amount at 45
ips). Due to non-linearity of the tension arm transducer the
swing of the tension arm may be unsymmetrical in the for-
ward and reverse drive modes. (This will mean the tension
arm will not be centered when there is no tape motion and
is normal.) With the supply reel loaded with approximately
200 feet of tape, rotate the supply (upper) variable resistor
(R106) fully clockwise and run the tape unit in the forward
mode. Rotate the supply (lower) variable resistor counter-
clockwise for the proper deflection. Stop tape motion and
put in reverse drive and make sure the amount of deflection
is the same as in forward drive. If not, readjust the mask
position until symmetrical swings of the proper amount are
achieved. Repeat procedure for the take up reel with approxi-
mately 200 feet of tape on the takeup reel.
Part 2