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If
you have a spectrum analyzer which covers 0-50kHz or so, the easiest way to
test
for
this
is to observe the spectrum of the signal at the left and right TEST
JACKS
when both channels are driven by pink noise at a level sufficient to cause
the TOTAL
MASTER G/R
meter to read " 0". Once this G/R meter
indication
is
obtained,
switch
the
COMPRESSOR
PROOF/OP
switch
to
PROOF
to
grossly
overdrive the clippers and overshoot compensator, thus stressing the system highly.
If one channel shows much more " trash" beyond 15kHz than the other channel, the
channel showing the excess " trash" is suspect.
EMERGENCY BYPASS
If
the
Card Swap Technique above reveals that
either Card # 0 or # 1 is
faulty,
OF CARDS #0 AND #1
both cards can be removed for servicing while keeping OPTIMOD-TV on the air on
an emergency basis. Basically, this involves re-routing the signal directly from Card
#6 to Cards # 8 and # 9, and re- activating the normally dormant clippers on Cards
#8 and # 9. This mode of operation is identical to that used in the old OPTIMOD-
TV
Model
8180A
and
in
OPTIMOD-FM,
and
therefore
does
not
involve
serious
compromises in quality: The " emergency" can last as long as necessary without any
penalty
other
than possibly a slight
increase
in clipping distortion
on low- quality
feeds like optical film.
CAUTION!
Do
not
try
to bypass
only
one
card
while
leaving
the
good
card
in
service:
In
stereo
operation,
you
will
experience
severe
phase-
cancellation in the mono sum because the delays in the left and right
channels
will
be
radically
different!
In
addition,
because
the Loudness
Controller
operates
from
the
sum
of
the
channels,
it
will
work
incorrectly.
Procedure:
1)
Remove Cards # 0 and # 1 from their slots.
2)
Remove Card # 6 from its slot. Remove the links from jumper "B" and place
them on jumper " C" as shown in Fig. F-1. Then move the link on jumper " A"
as shown in Fig. F-1. Replace Card # 6 in its slot.
(NOTE: Jumper " C" permits swapping channels at the output
of Card # 6 for
trouble diagnosis even in the " emergency" mode.)
CIP—¡ R.G8
pt.
•4.5.
HI)
_
•!;
It
'eg
5
r,mICR
cm)
ty
,
ff
o
re2c±1..
RtvER•e.
• •
• •
Fig. F-1: CARD # 6: JUMPER LOCATIONS
F-5
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