Orban 424A - 43 Appendix B: Specifications; Part D: Maintenance

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