Using - Orban 412A Operating Manual

1:
ALIGIMMEIMT
AND
PERFORMANCE
EVALUATION
PART
D:
Maintenance
Introduction: This part
of
the
manual
provides instructions
on
how
to
maintain the
414A,
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
414A. Please refer
to
Factory Service subsection of
MAINTENANCE
AND
SERVICE
below
for
further
information.
CAUTION
Service
instructions are included for use by qualified
personnel
only.
To
avoid electrical
shock,
do
not
perform
servicing other than that
described within Operating Instructions unless
you are qualified
to
do
so.
Refer
all
such servicing to
qualified service personnel.
General:
This procedure refers to the
414A
(dual-channel version),
but
is
equally applicable
to the
412A
(single-channel version). This
section provides a series of
thorough
bench
tests
which
will
usually
verify
whether
or
not the
414A
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
414A. Such
subtle
failures are
usually detected by ear
in
the field,
and factory
service
is
recommended.
In
the case
of
the
dual-channel 414A, the
completely redundant channels
make
"by
ear" trouble diagnosis easier, as
the
bad channel can
be directly
compared
with the
good
one.
The
414A
is
aligned as these
tests are
performed.
The 414A
has five
trimmers per
channel (which
standardize
VGA
gain,
calibrate the
meter,
and
which
null
DC
offset,
thump and distortion).
Alignment
is
ordinarily
required only
when 1C3, 1C13,
or
1C14
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,
IC13 and IC12.
The
supplies should deliver
between
+14.25 and
+15.75
VDC.
If
either
suppiy
exceeds
15.75
VDC,
it
implies
that
its
associated IC regulator
is
defective.
If
either supply
is
lower
than 14.25
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
2mV
peak on
each
bus.
21