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3.
R626 ( left
channel)
or R660 (right
channel)
misadjusted,
such
that
IC603A
(left
channel)
or
IC603B ( right
channel)
is
always
turned
ON,
thus
partially
defeating the preemphasis.
4.
HF
limiter
working
too
hard.
Check
IC605B,
IC607 ( left
channel);
IC611B,
IC612 ( right
channel)
for
correct
rectifier
action
and
correct
HF
limiting
threshold. ( These
circuits
are
independent.
Thus,
the
bad
channel
can
be
compared to the good channel with a mono source.)
Gross distortion.
1.
Power supply voltage low. (Check AC power line voltage first.)
2.
IC opamp failure. This must be diagnosed by signal tracing.
3.
Failure
in clipper- diode bias supplies. Low bias voltage will cause excessive
clipping, and will also result in abnormally low modulation. Check IC806B, IC808
and
associated circuitry ( on Cards # 8 and # 9) to make sure that the output
is
approximately + 1.5VDC
under
no- signal
conditions,
and
approximately + 1.35VDC
when
a 5kHz sinewave at level sufficient to cause gain reduction is applied to
the
input
of
the
appropriate channel. Check IC613 and
associated circuitry ( on
Card # 6)
to
make
sure
that
the
output
is
approximately + 4.2VDC
under
all
OPERATE conditions.
4.
Gross failure in a sidechain, such as IC latchup. This will either misbias the
main signal path, or add distortion to the main signal, without causing the main
signal to disappear. IC's in sidechains include IC601A, IC608A, IC602B, IC609B,
IC604, IC610 ( on Card # 6); IC802A, IC802B, IC803A, IC804A, IC804B ( on Card # 8
and Card # 9).
5.
Exponential converter(s) IC501, IC502, IC510, IC511, or timing module(s) Al,
A2 ( on card # 5) defective, causing very low ( or no) control current to VCA's on
Cards # 3 and # 4, thus causing these VCA's to take very high gain. Timing module
failure will be indicated by COMPRESSION MASTER G/R or BASS G/R meter's
pegging at the top of the scale (beyond "+ 10").
6.
Failure
in
Hilbert- Transform
Clipper
control
circuitry,
particularly
that
causing the threshold of limiting to be excessively low.
Moderate to Subtle Distortion.
1.
Distorted
program
material
and/or
distortion
problems
in
studio
or
STL.
2.
Check points
listed
in " Gross Distortion" ( immediately
above),
for
moderate
deviations from normal parameters.
3.
CLIPPING control misadjusted.
4.
Failure
in rectifiers IC507A, IC505, IC507B,
IC506,
IC514A,
IC512,
IC514B,
IC513,
or
in timing modules Al, A2 on card # 5. These problems will usually be
indicated by failure to produce standard level under standard conditions ( see c.1
and c.2 in Appendix D).
5.
Safety clipper misalignment ( R841). This alignment is most unlikely to drift
by
itself
from
its
factory- adjusted
condition.
But
humans
with
alignment
tools
sometimes do strange things. If you are in doubt about this alignment, it can be
checked ( and
readjusted
if necessary) by
performing
the
Card # 8/9
alignment
procedure in Appendix E.
6.
Phase
corrector
failure.
See " Phase
Corrector
Failures"
earlier
in
this
Appendix for a further discussion.
7.
Failure in distortion- cancel sidechain on Cards # 8 and # 9. This is indicated
by a " gritty" high end with severe sibilance splatter.
8.
Misalignment of DISTORTION NULL controls on VCA's on Cards # 0, # 1, # 3,
or #4. Such misalignment will introduce mainly second- harmonic distortion, which
might actually sound pleasing on some program material.
F-8
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