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7970B/7970C
3-24.
REGULATED SUPPLY VOLTAGES. Regulated
voltages will remain within tolerances over a primary voltage
range of ±10 percent. DC voltages and tolerances are to be
as specified below. The peak-to-peak ripple values are nom-
inal and minor variances may be expected. Ripple is stated
under tension-only conditions.
a. The +5 volt supply must be +5.000 ± 0.050 Vdc.
b. The ±12 volt supplies must be 12.000 ± 0.360 Vdc.
3-25.
UNREGULATED SUPPLY VOLTAGES. Unregu-
lated supply voltages are a direct function of line voltage.
The following table of nominal values should be judged
only at a line voltage of 115 volts. RMS ripple values are
nominal and apply at 60 Hz.
a. ±40 Vdc: Nominal value is ±57.5 volts; ripple of
150 mv POp (sawtooth).
b. +20 Vdc: Nominal value is +22.5 volts; ripple of
600 mv Pop (sawtooth).
c. -20 Vdc: Nominal values is -22.5 volts; ripple of
300 mv Pop (sawtooth).
d. +10 Vdc: Nominal value is +12 volts; ripple of
900 mv POp (sawtooth).
3-26.
TAPE SPEED AND CAPSTAN SERVO CHECKS.
3-27.
The tape speed and capstan servo checks consist of
measuring capstan motor offset current, measuring long term
speed variation (tape units capable of reading data), measur-
ing start and stop time and distance, measuring instantaneous
speed variations, and measuring fast forward, reverse, start
and stop. Included is a dynamic tape skew check for tape
units equipped with read and write electronic circuits.
3-2S.
CAPSTAN MOTOR OFFSET CURRENT. Connect
a suitable dc voltmeter or oscilloscope across the 3 ohm 1
percent resistor (R21 or R22). The return side of the resis-
tors is connected to pin 2 of CJ-1. With the tape under ten-
sion but no tape motion, the voltage should not exceed the
following referenced to 0 V dc.
a. Maximum acceptable operating limit: ±100 mv dc
at 25°C.
b. Adjustment recommended if greater than: ±SO mv
dc.
3-29.
LONG TERM SPEED VARIATION. Measure the
tape speed accuracy over any interval greater than one sec-
ond and under each of the five drive speeds. The principle
of measurement requires that a tape having highly accurate
Part 2
Performance Checkout
bit-to-bit distances be read, and that the output of the read
preamplifier be connected to a suitable counter. HP part
number 50S0-4525 Transport Test Tape provides frequencies
accurately spaced to better than 0.1 percent. For the follow-
ing tests reference frequencies are based on using the signal
that will be avail abel from the channel 3 preamplifier of nine-
track units and channel 6 preamplifier of seven-track units.
This has a bit-to-bit spacing of 0.00150 inch and will pro-
duce a frequency of 10,000 Hz when reproduced at a tape
speed of 30.000 ips. Frequencies for other speeds are in
direct ratio to the change in speed relation to 30 ips. Ex-
ample: 60 ips would produce 20,000 Hz. Use this principle
and check the following:
a. High-Speed Forward: 160 ips, basic frequency is
53,333 Hz.
(1)
Maximum acceptable operating limit: ±1050
Hz (±2 percent).
(2)
Adjustment recommended if greater than:
±SOO Hz (±1.5 percent).
b. Rewind (High-Speed Reverse): Checked identically
to the limits applicable to high-speed forward, except that
the rewind mode is used.
c. Forward and Reverse Drive: Frequency depends
on tape speed and must be calculated for speeds other than
25 ips and 37.5 ips which are tabulated below. Maximum
acceptable operating limit is based on ±1 percent with ad-
justment recommended if speed error is +O.S percent or
greater.
(1)
The 25 ips drive nominal frequency is S,333
Hz. Acceptable limits are ±S3 Hz; adjustment
is required if greater than ±65 Hz.
(2)
The 37.5 ips drive nominal frequency is
12,500 Hz. Acceptable limits are ±125 Hz;
adjustment is recommended if greater than
±100 Hz.
d. Load Point Search: 20 ips; basic frequency is
6,667 Hz.
3-30.
(1)
Maximum acceptable limit is ±1330 Hz (±20
percent).
(2)
No adjustment is provided.
START MEASUREMENT. Start measurements
(both forward and reverse) are made as follows. Measure-
ment of the characteristics defined requires that the tape
unit be driven with commands that are adjustable to periods
greater than the specified start/stop times and that there be
a provision to synchronize an oscilloscope sweep directly
from these commands (both start and stop). The tape to be
read may be any previously recorded tape, preferably at
SOO cpi, as this provides the best resolution where measure-
ments from preamplifier outputs are required. Wavelength
3-3
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