THEORY OF OPERATION-MAI NTENANCE(continued)
1
Electrical Adjustment Procedure
I
Six tracks still remain to be checked and adjusted, but
as
you can see, the adjustments are the same as for
track 1. In brief:
1. play the tape "operating level"
2.
read the VTVM for head
3,
MONITOR
3. adjust for -10
dB (0.3 V) reading with trim pot
#l
4. switch to NORMAL on OUTPUT SELECT
5.
read the VTVl\rl. Adjust trim pot
#2
6. read the meter on the 80-8
-
it
must read
O
VU
7.
adjust th-e meter trim pot #3 R105,
22
k
Ohms
METER CAL
You do this for
al1 8 tracks: 16 level sets and, if
necessary, 8 meter trims. Don't get discouraged. When
you are unfamiliar with anything,
it
takes more time.
Practice will speed things up. The entire adjustment
procedure involves reading and setting
(if necessary)
about 128 controls. When you are used to doing it, it
should only take about an hour and
a
half. Have
patience, you'll learn soon enough.
It
is
absolutely
worth
it.
One more word of encouragement. The circuits in the
80-8 are very stable. Most of the
time you will make
a
reading and not have to adjust anything. When some-
thing does go wrong, you will be able to fix
it
very
quickly, and get back to recording.
In summary, with the VTVM and test tape, you
have
adjusted the playback level on the 80-8 to the test
tape. But your play back reference is not yet complete.
You
have only "zeroed" one point on a line of
frequency response. To establish the rest of the
line,
you must measure and adjust one more frequency.
Advance the alignment tape for 15 ips to'the section
that
is
recorded
at
16 kHz and adjust the trim pot
marked MONIT
EQ
#4 R102,6.8 k Ohms
-
switch to
NORMAL on the OUTPUT SELECT, and adjust trim
pot
#5, R101, 6.8 kOhms NORM
EQ.
The reading for
both positions
should be -10 VU on the 80-8 meters.
Since you have checked and adjusted the playback
meter circuit, you now
can use the meters on the80-8
for the test readings.
By adjusting
al1 of the preceding trimmers, you have
established two things: an operating playback level or
"zero", and
a
playback frequency response reference.
You know that both heads on the 80-8are reproducing
the test tape in an
identica1 manner.
RECORD CALIBRATION:
VTVY
1
Fig.
22
Test
Connection for Recording Check
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