Advertisement
Then, contact the Customer Service Department by telephone, letter, or Telex ( see
title page for numbers). A Customer Service Engineer is ordinarily available during
local business hours, Monday through Friday. The Customer Service Engineer will do
everything practical to help correct the fault and have your OPTIMOD-TV up and
running again as quickly as possible.
In
many
cases,
field repairs
can be effected by
merely exchanging
a single PC
card,
rather
than
by
returning
the
entire
OPTIMOD-TV
chassis
for
repair.
The
factory ordinarily maintains a small number of " loaner cards". One of these may be
provided as a spare PC card for use while the customer's card is being repaired at
the factory. In most cases, factory service of defective cards is preferable to field
service
by
the
customer
because
the
factory
maintains
a supply
of
exact- replacement spare parts, and has the experienced technicians and special test
fixtures necessary to assure that the repaired card meets factory specifications in
all respects. Instructions for packing and shipping cards or the complete chassis are
found at the end of this Appendix.
DIAGNOSIS AT THE
After
following the above diagnostic procedure to localize the problem to a single
COMPONENT LEVEL
card,
you may
want
to
troubleshoot
the card on
the component level
instead of
returning the card to the factory for service.
Here are some suggestions...
Troubleshooting IC Opamps
IC opamps are
operated
such that
the characteristics of their associated
circuits
are
essentially
independent
of
IC
characteristics
and
dependent
only
on
external
feedback components. The feedback forces the voltage at the "-" input terminal to
be
extremely
close
to
the
voltage
at
the "+"
input
terminal.
Therefore,
if
the
technician measures more than a few millivolts between these two terminals, the
IC is probably bad.
Exceptions are IC's used without feedback ( as comparators) and IC's whose outputs
have
been
saturated
due
to
excessive
input
voltage
because
of
a defect
in
an
earlier stage. However, if an IC's "+" input is more positive than its "-" input, yet
the output of the IC is sitting at - 14 volts, this almost certainly indicates that it
is
bad.
The
same
holds
if
the
above
polarities
are
reversed.
Because
the
characteristics
of
OPTIIv10D-TV
are
essentially
independent
of
IC
opamp
characteristics,
an
opamp
can
usually
replaced
without
need
for
recalibration.
NOTE
THE
DUAL
CURRENT- CONTROLLED
GAIN
BLOCKS
EMPLOYED
IN
THE VCA's(IC 305, 309, 405, dc 409 on Cards # 3 and # 4; and IC 1 (1c 11
on
Cards # 0 and # 1) ARE NOT
OPAMPS.
IF
THEY ARE
REPLACED,
RECALIBRATION IS ABSOLUTELY NECESSARY.
A
defective
opamp
may
appear
to
work,
yet
it
may
have
extreme
temperature
sensitivity.
If
parameters
appear
to
drift
excessively,
freeze- spray
may
aid
in
diagnosing
the
problem.
Freeze- spray
is
also
invaluable
in
tracking
down
intermittent
problems.
But,
use
sparingly,
because
it
can
cause
resistive
short
circuits due to moisture condensation on cold surfaces.
Advertisement
