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APPENDIX F:
Trouble Diagnosis and Correction
This Appendix is the first place you should go to obtain information on what to do
if OPTIMOD-TV develops a fault.
Many
problems experienced in the field can be resolved or conclusively diagnosed
with the following
diagnostic routines. Even
if the repair cannot be
done in
the
field, the information provided by these diagnostic routines can speed the work of
the factory service department in making the repair. Please perform these routines
and make notes if you observe anything exceptional or unusual.
1)
Use
systematic
troubleshooting
techniques
to
positively
determine
that
the
problem is in fact being caused by OPTIMOD-TV and not by other equipment. If
a standby processor is available, it should be substituted for the supposedly faulty
unit to see if the problem vanishes. If a standby processor is not available, audio
quality at the OPTIMOD-TV audio input terminals should be checked with a high-
quality
monitor
system.
Note
that
even
slight
distortion
can
be
seriously
exaggerated by " heavy" processing, and that this sort of processing can only be
successful
if
the
input
audio
is
extremely
clean.
A relatively
minor
problem
which develops in the station's audio chain or STL can therefore be magnified by
the
action of OPTIMOD-TV, even if the unit is in no way defective. This is a
further
argument
for
adjusting
the
OPTIMOD-TV
controls
conservatively
to
produce low distortion and superior high frequency response.
If
the
audio
is clean
going into OPTIMOD-TV,
problems can still
arise in the
aural exciter. If a standby exciter is available, it should be substituted to see if
the
problem
vanishes.
If
no
standby
exciter
is
available,
you
can
connect
the
audio
output
of
OPTIMOD-TV
directly
into
a high- quality
amplifier
and
loudspeaker
to see if the problem can still be heard. If you ordinarily operate
un-deemphasized, then you should first remove Card # 7 and move the jumpers to
the
deemphasized position ( see Part 3: Installation) in order to hear flat sound
from the audio monitor. If the problem vanishes when you observe the output of
OPTIMOD-TV directly, then the exciter ( or phase- linear STL, if used) is strongly
suspect.
Changes
in
or
deterioration
of
grounding
and/or
exterior
lead
dress
can
sometimes
cause
RFI
or
hum
problems
to
appear
in
a correctly- operating
OPTIMOD-TV.
If
it
seems impossible to conclusively isolate the problem to OPTIMOD-TV, yet
no other definite cause is found, then performing the Field Audit-Of-Performance
procedure in Appendix D may help diagnose a problem.
2)
if
the
fault
has
been
positively
isolated
to
OPTIMOD-TV,
the
Problem
Localization Routine described below should be performed to identify the faulty
PC card.
PROBLEM
LOCALIZATION
ROUTINE
General
Principles:
The
most
powerful
and
general
technique
for
localizing
a
problem within OPTIMOD-TV is signal tracing. This simply means that the signal is
observed at various points as it passes from OPTIMOD-TV's input to its output. If
the
signal
is normal at some point " A" in the circuit, and is abnormal at a point
"B"
further towards the output, then the problem clearly lies in circuitry between
points " A" and " B".
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