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In
addition, the GATE must be
defeated.
This
is done by gaining
access to the
circuit
cards [ following
the
instructions
in
Appendix C (User Access)].
Turn
off
AC power. Then remove Card # 5 from its slot, and temporarily remove 10508 from
its socket. ( To locate 10508, refer to the Card /15 Assembly Drawing in Appendix
J.)
Replace Card # 5 in its slot and restore AC power. ( There is no need to replace
the subpanel now unless high RF fields are present.)
Using
its
local
OPERATE/DEFEAT
switch,
switch
the
Loudness
Controller
to
OPERATE, and verify that its green LED glows.
Make
sure
that
both channels of OPTIMOD-TV
are being driven
in
parallel
from
the oscillator, and that the OPTIMOD-TV INPUT ATTEN controls are balanced such
that
equal readings are produced when the OPTIMOD-TV VU meter is observed in
its L COMPR OUT
and R COMPR OUT positions. Set the oscillator frequency to
3kHz and adjust its output level to produce a reading of "- 10" on the OPTIMOD-TV
TOTAL
MASTER G/R meter. Then observe the OPTIMOD-TV VU meter in the L
COMPR
OUT position and verify that the following readings are produced at the
following frequencies, + 2VU:
FREQUENCY
VU METER READING
300 Hz
0 VU
500 Hz
- 5
700 Hz
- 6
1 kHz
- 7
2 kHz
- 11
3 kHz
- 14
4 kHz
- 14
5 kHz
- 13
7 kHz
- 10
10 kHz
- 6
TABLE D-3
If
the readings vary substantially from those provided in Table D-3, the Loudness
Controller circuitry is suspect. The most likely problem is a complete failure in one
filter
band ( due
to
a defective
opamp).
However,
faults
in
passive
components
within the filter circuitry can also cause difficulty. If diagnosis cannot be made by
identifying
a dead
band
or
other
obvious
cause,
we
advise
sending
Card # 2
(Loudness
Controller)
back
to
the
factory
for
service
so
that
the
frequency
responses of the individual filters can be accurately verified. OPTIMOD-TV operates
normally ( except
for the loss of
the Loudness Controller
function) with Card # 2
removed.
When
you
have
finished
testing
the
Loudness
Controller,
remove
AC
power
to
OPTIMOD-TV. Replace IC508 in its socket on Card # 5, carefully verifying that the
end
of
the IC with a notch is at the end of the socket marked with a square or
small
flag on the circuit board foil. ( Check the Assembly Drawing for Card # 2 in
Appendix J if there is any question.) If the IC is installed backwards, it will be
instantly destroyed on powerup!
Then
reinstall
Card # 5 in
its
slot,
and
replace
the
subpanel,
following
the
instructions in Appendix C (User Access).
For
further
discussion
of
Trouble
Diagnosis
and Correction,
see
Appendix F.
D-5
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