Part D: Maintenance - Orban 424A Operating Manual

Part D:
Maintenance
Introduction: This part of the
manual
provides instructions on
how
to maintain the
424A,
how
to
make
sure that
it
is
working according
to
specifications,
and
how
to
repair
it if
something goes wrong.
Factory
service
is
available
throughout the
life
of the
424A.
Please refer to
Factory Service subsection
of
MAINTENANCE AND
SERVICE
below
for
further
information.
1
:
ALIGNMENT
AND
PERFORMANCE
EVALUATION
General:
This procedure
refers to
the
424A
(dual-channel
version),
but
is
equally applicable
to the
422A
(single-channel version). This section provides a
series of
thorough
bench
tests
which
will usually verify
whether
or not the
424A
is
operating
normally. Certain subtle failures
in
the
dynamic
control circuitry
cannot be
detected by these
tests,
since
special
factory
test
procedures and equipment
are
necessary
to fully
characterize
the
dynamic
operation
of
the
424A. Such
subtle
failures
are usually detected by ear
in
the
field,
and factory
service
is
recommended.
In
the
case
of
the dual-channel 424A, the completely redundant channels
make
"by
ear" trouble diagnosis
easier, as
the bad channel can be
directly
compared
with the
good
one.
The
424A
is
aligned
as
these tests are
performed. The 424A
has four
trimmers
per
channel (which
null
thump
and
distortion,
and standardize
VCA
gain).
Alignment
is
ordinarily required only
when
IC5, IC6, IC7, IC8, or 1C
13
is
replaced.
Power
Supply:
Equipment
Required:
1)
VTVM
or
DVM
2)
Oscilloscope
The
following
tests
will
verify correct operation
of the
Power
Supply:
1)
Using
the
DC
voltmeter,
measure
the voltage from
circuit ground
to
both
positive
and negative unregulated
supplies. This can
be readily
measured
across
the two
large
filter
capacitors. This voltage may
be expected
to
vary widely
depending on
line
voltage;
it
should
measure between
+18 and +26
volts
DC.
2)
Measure
the voltage between
circuit ground and
the outputs of the positive
and
negative
voltage
regulators, IC5 and
IC6.
The
supplies should put out
between
+14.25 and
+15.75
VDC.
If
either supply exceeds
15.75
VDC,
it
implies
that
its
associated 1C regulator
is
defective.
If
either supply
is
lower
than
1
4.25
VDC,
refer to the Power
Supply portion of
Part 3
in this
section
for troubleshooting
hints.
3)
Using
the oscilloscope,
measure
the ripple and noise on
the regulated positive
and negative power
busses. Ripple and
noise should be
less
than
4mV
peak on
each
bus.
21