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8: CARDS #8
This procedure is performed twice -- once for Card # 8, and once for Card # 9.
AND #9
Only Card # 8 will be referenced.
a)
Extend Card # 8.
b)
Connect
the
oscillator
to
the
left
OPTIMOD-TV
input.
Set
both
PROOF/OPERATE switches to PROOF. Connect
the AC VTVM
to the input
of
Card # 8 ( input side of R801). Set the oscillator frequency to 100Hz, and adjust
the oscillator output level until - 3.9dBm is observed on the VTVM.
c)
Adjust
R841 (SAFETY
CLIPPER
THRESH)
to
produce
OdBm
at
pin
7 of
IC806A ( pin
X of
the
card
connector).
This
sets
a standard
gain
of + 3.9dB
through the card.
d)
OPTIONAL PERFORMANCE VERIFICATION Of Filters
1)
Connect
the output
of the 5L4N tracking generator to TP1
of Card # 8
(pin L on the card connector). Connect the input of the 5L4N to the left rear-
panel TEST JACK. Observe the swept response with the 5L4N vertical span at
10dB/div, with 20-20kHz log frequency sweep.
The swept response shows the
response of the 2.2-15kHz bandpass filter which is created by subtracting the
output
of
the
2.2kHz
lowpass
filter
from
the
output
of
the
15kHz
lowpass
filter.
Note the high amount
of rejection below
2.2kHz,
and
the
very steep
slope at 2.2kHz (see Fig. E-3).
Fig. E-3: 2.2-15KHZ BANDPASS FILTER RESPONSE
If
this
swept response
does
not resemble Fig. E-3,
then there
is
a fault
in
either the filters or phase correctors between the card input and the output of
IC803B.
This
test
is
both
fast
and
sensitive
because
accurate
cancellation
demands accurate matching of the phase and amplitude responses of both the
phase- corrected
15kHz
lowpass
filter
and
the
2.2kHz
lowpass
filter.
If
any
circuitry is faulty, then the cancellation will not occur accurately.
2)
Temporarily remove Card # 6 from
its slot. Then measure the clipper bias
voltages
at the outputs of IC808A and IC808B. These should be approximately
+1.5VDC
with
no
signal.
( NOTE:
The
temperature- compensation
circuitry
will
cause this bias voltage to change slightly with temperature to keep the clipping
threshold constant.)
Replace Card # 6 in its slot.
E-7
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