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5-2
TROUBLESHOOTING
Orban Model
464A
Problems
and
Possible
Causes
Always
verify
that
the
problem
is
not
in
the
source material being
fed
to
the
Co-
Operator, or
in
other
parts
of
the
system.
RFI,
hum,
clicks,
or buzzes:
A
grounding problem
is
likely.
Review
the information
on
grounding
in
Section
2.
The
Co-Operator's moderate
RF
suppression
it
should
be adequate
for the vast
ma-
jority
of
installations.
However,
installation
next
to
a
high-power
transmitter
may
still
cause problems. Additional
RF
suppression, careful
examination of
the
ground-
ing
scheme, and
other techniques
familiar to the
broadcast engineer
may
have
to
be
employed.
Power
supply problems:
The
voltage
regulators are
operated
conservatively,
and can be expected
to
be
ex-
tremely
reliable.
Before
replacing the
regulators,
check
to see
whether
other abnor-
malities in the
circuitry
(such
as a shorted
IC)
have
caused excessive
current
demand
which
is
in
turn
causing
the regulator
ICs
to either current limit
or
go
into
thermal
shutdown
(the
two
built-in
protective
modes).
If
it
becomes
necessary
to replace a
regulator,
be
sure
to
replace
its
heat
dissipator properly.
Regulators
IC8 and IC7
are
frequency-compensated
by
C4,
C5
at their
outputs
to
prevent high-frequency
oscillations.
If
C4
or
C5
is
ever
replaced,
be
sure
to
use
a low-inductance
aluminum
electrolytic.
(A
tantalum
can
fail
because
the current-
delivering capacity
of
the
power
supply can cause a
runaway
condition
if
the
dielectric
is
punctured momentarily;
a high-inductance
aluminum
can
fail
to
prevent
a regulator
from
oscillating.)
Check
for oscillation
on
the
power
bus with an
oscilloscope
if
C4
or
C5
is
replaced.
Poor
peak
control:
Check
that the
peak
clippers are
enabled:
jumper
A
on
the
main
circuit
board should
be
in the
"OPERATE"
position (see
Fig. 2-1).
Apparent peak
control
problems
may
actually
result
from problems
with
the
device
the
Co-Operator
is
driving.
A
digital
tape recorder
or
FM
transmitter, for
example,
could
introduce
overshoot and
ringing.
A
device with
poor
frequency response might
cause
"tilt"
with low-frequency
material.
Be
sure
that the
instrument
used
to
measure
the
peak
output of
the
Co-Operator
(or
the
device
it is
driving)
has
accurate
transient
response
and
dynamic
accuracy.
Shrill,
harsh sound:
This could
be
caused
when
the
Co-Operator
is
supplying pre-emphasis
to
a
device
that
doesn't
need
it
If
the
device driven
by
the
Co-Operator does
not
require pre-
emphasis, place
jumpers
B
and
C
on
the
main
circuit
board
in
the
"FLAT"
position
(see Fig.
2-1).
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