Record Alignment; Record Bias Set; Equalization Pwa Adjustments; Regulator, Bias Oscillator And Amplifier Pwa - Scully 280B Series Instruction And Maintenance Manual

7-12
Maintenance
Figure 7-13. Equalization PWA Adjustments
D. Following instructions from the standard test
tape, adjust equalization for flattest response.
Adjust HF HI for high speed and HF LO at
low speed (Figure 7-13). Low frequency ad­
justments should be made in Record mode in
order to compensate for fringing effects on
multi-track machines.
E. Set Function switch to SYNC position.
F. At corrected (250 nWb/m) reference tone
from the standard test tape, adjust sync level
potentiometerR7(Figure 7-14) on the record/
playback amplifier PWA for 0 vu, (+4 dBm on
external meter).
NOTE
The standard opera ­
ting level (play back
fluxivity) is as follows:
3.75 & 7.50 in/s
==
200 nWb/m at 1000 Hz
7.50
&
15 .00 in/s
==
250 nWb/m at 1000 Hz
15.00
&
30.00 in/s
==
250 nWb/m at 1000 Hz
Model 280B
7.13 Record Alignment
A. Connect oscilloscope to the yellow test point
(TP1) on the regulator, bias oscillator, and
amplifier PWA (Figure 7 -15).
B. Adjust bias level potentiometer R IO on the
regulator, bias oscillator, and amplifier PWA
for 40 volts p-p using the oscilloscope.
C. On four-track systems, repeat steps A and B
to adjust R6 on the bias amplifier PW A (Fig­
ure 7-16) for channels three and four.
D. Install 3M 206 tape or equivalent.
E. Set Function switch to RECORD and CAP­
STAN speed switch to HIGH.
F. Press START and then RECORD pushbut­
tons on transport.
G. Visually align record head height to corres ­
pond with playback head.
H. Record 15 kHz at -10 vu.
I. Adjust record head azimuth and check head
rotation for proper gap contact.
7.14 Record Bias Set
A. Record 10 kHz at approximately zero vu
level with Monitor switch in PLAYBACK
position (-10 vu for 7.5 to 3.75 in/s machines).
B. Rotate R6 bias adjust on the record/playback
amplifier PWA (Figure 7 -14) until a peak read­
ing is indicated on the vu meter.
C. Rotate the bias adjust potentiometer in a CW
direction (increasing bias) until the level on
the vu meter drops exactly 4 dB for 3.75 to
7.5 in/s machines at the 7.5 in/s speed, and
2 dB for 7.5 to 15 and 15 to 30 in/s machines
at the 15 in/s speed.