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If
the
signal
is
normal
at
the
COMPR
OUT
positions,
but
abnormal
in
either
FILTER OUT position, then the problem may lie with Card # 6 ( which contains both
channels), Card # 0 ( left channel), Card # 1 ( right channel), Card # 8 ( left channel),
or Card # 9 ( right channel).
If
the
signal
is
normal
at
both FILTER
OUT
positions,
but
abnormal
at
either
SYSTEM
OUT
position,
then
the
problem
lies
in
Card # 7 ( line
amplifiers).
The
Card Swap Technique might be used to localize the problem more precisely.
CARD SWAP
The instructions below provide more detailed information on troubleshooting at the
TECHNIQUE
" card
exchange"
level.
Servicing
on
the " component
replacement"
level
requires
more profound understanding of OPTIMOD-TV circuit operation, which is provided by
Appendix A ( SYSTEM DESCRIPTION) and Appendix 8 ( CIRCUIT DESCRIPTION). If
the
technician wishes to troubleshoot at the component level, he should first use
Appendix A to help track down the fault to a given subsystem, and then refer to
Appendix B for an extremely detailed explanation of the circuitry at the component
level.
If
the
defective
card
has
not
yet
been
conclusively
identified
and
if
the
fault
appears on one channel only, the next step involves a card swap technique. The PC
cards in OPTIMOD-TV have been specifically configured to aid troubleshooting if a
fault
appears in one stereo channel only. Cards # 0 and # 1, Cards # 3 and # 4, and
Cards # 8 and # 9 are identical. Therefore, these card pairs can be interchanged one
pair
at
a time
to
see
if
the
problem
moves
from
one
channel
to
the
other
(implying that the fault is with one of the cards just moved), or stays the same
(implying that the problem lies elsewhere in the system).
If the card swap technique reveals that either Card # 0 or Card # 1 is faulty, the
system
can
be
operated
without
these
cards
by
following
the
instructions
in
Emergency Bypass Of Cards # 0 and # 1, below.
If
interchanging these card pairs fails to affect the location of the problem, then
Card # 6 should he investigated. This card passes both left and right audio. To aid
troubleshooting, jumper " B" is provided at
the output
of
the card to
interchange
the outputs of the left and right channels ( See Fig. F-1). Jumper " B" contains links
if the system
is operating in its " normal" mode ( with Cards # 0 and # 1 present). If
this
jumper
is
moved and the
fault
moves
from
one channel
to the other, then
Card # 6 is probably faulty.
(Jumper " C" will contain links if the system is operating in its " emergency" mode.
In
this
mode, moving the links on jumper " C" will perform the same function as
moving the links on jumper " B" in " normal" mode, so diagnosis of problems in Card
#6 can still occur.)
Problems
in
Card # 7 ( Line
Amplfiers)
are
unlikely
because
the
circuitry
is
so
simple. If one channel of Card # 7 is bad, audio will be normal
at the rear- panel
TEST
JACK corresponding to that
channel, and abnormal at that
channel's MAIN
AUDIO OUTPUT.
Cards
Common
To
Both
Channels:
Cards # PS ( Power
Supply), # 2 ( Loudness
Controller),
and # 5 ( Compressor Control
Circuitry) are common to both
channels.
Card # 6 contains the common + 4.2V clipper bias supply used by Cards # 8 and # 9.
Diagnosis of power supply problems was discussed above.
F-3
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