Table of Contents
Advertisement
7970B/7970C
and offset current are within tolerance. Figure 5-3 shows
the location of service switches and forward and reverse
drive adjustment potentiometers.
5-29.
Accurate adjustment is based on reading (into a
counter) data bits that have been recorded with high aver-
age accuracy. The 5080-4525 Test Tape has bit-to-bit ac-
curacy of better than 0.1 percent when measured over 2000
bits or more. In using this tape, it is important to recognize
that there are two data bits for each cycle counted when the
counter is connected to the preamplifier analog output sig-
nal, and also that the frequency at other than the specified
tape speeds may be calculated on a direct ratio basis. The
signal used for the following adjustments appears in pre-
amplifier channel 3 of nine-track units and preamplifier
channel 6 of seven-track units. The test tape provides a sig-
nal of 10,000 Hz at a tape speed of 30 ips and has a bit-to-
bit distance of 0.0015 inch.
a. Load test tape and place unit in forward drive
mode using FWD service switch (S2).
b. Adjust the FWD synchronous control (R34) until
counter indication is correct for the tape speed involved.
The values for speeds of 25 ips and 37.5 ips will follow.
Values for other speeds may be readily calculated by direct
ratio to speed and application of the percentage tolerances
indicated.
c. For 25 ips speeds, the counter indication should be
8,333 ± 16 Hz when adjustment is completed. No adjustment
is necessary as long as counter indication is within ±65 Hz.
d. For 37.5 ips speeds, the counter indication should
be 12,500 ± 25 Hz. No adjustment is necessary if reading is
within ±100 Hz.
e. Repeat steps "a" and "b" with unit in reverse drive
mode.
5-30.
CAPSTAN SERVO HIGH-SPEED FORWARD
ADJUSTMENT.
5-31.
The high-speed forward adjustment principles and
requirements are the same as the forward and reverse drive
adjustment. Ensure that all previous adjustments are within
tolerance.
a. Load the test tape on the transport and connect
a counter to the appropriate channel preamplifier output.
b. Place unit in high-speed forward mode with the
high-speed forward (+160) service switch (figure 5-3), and
use the high-speed forward (+160) adjustment (R53) to ad-
just speed until counter indicates 53,333 ± 100 Hz. No ad-
justment is required if counter indicates between 52,533
and 54,133.
Part 2
Adjustment Procedures
Note
If high-speed forward is required for seven-track
tape units equipped with parity options and hav-
ing normal drive speeds less than 15 ips, high-
speed mode must not exceed a factor of 12
times the normal drive speed.
5-32.
CAPSTAN SERVO HIGH-SPEED REVERSE
ADJUSTMENT.
5-33.
The high-speed reverse adjustment is identical to
the high-speed forward adjustment, except that the local
REWIND control is used to place the unit in the high-speed
reverse mode and the high-speed reverse (-160) adjustment
variable resistor (R60, figure 5-3) is used.
5-34.
CAPSTAN SERVO RAMP SLOPE ADJUSTMENT.
5-35.
The ramp slope adjustment determines the start
and stop distances for both forward and reverse drive modes.
The following procedure describes how to adjust the slope
of the bi-polar ramp generator on the capstan servo PC as-
sembly. This adjustment sets the start distance to 0.1875
inch. The top of the ramp is rounded, therefore, the 90%
point ofthe voltage waveform is used. (See figure 5-4.)
a. Operate the tape unit in a forward-stop-forward
mode.
b. Connect an oscilloscope to the FWD/REV test
point on the capstan servo PC assembly. Sync the oscillo-
scope with the negative going edge of the forward com-
mand. (Test point 9 of the control and status PC assembly
or test point CF of the control and status test board.)
7970-476
1-1.
---T-----I"I
100%
18 DIVISIONS)
- - - - 9 0 %
17.2 DIVISIONS)
/----WAVEFORM AT
FWD/REV TEST POINT
~FORWARDCOMMAND
Figure 5-4. Start/Stop Ramp Time
5-5
Advertisement
Table of Contents
