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capabilities. The limit point is deltnnincd by a
combination
of
the
predriver
plus
limiter current equaling
the available current
source
on
the main board. In ollier
words, the
signal
drive that is
fed
to the predrivers
is
limited
or
clamped.
6.9IOe'"
The front-panellOC display
is actually
a
window
comparator
circuit using two
operationaJ
amplifiers
(IC3C.D)
and
an
LED md;cator
(E
102).
Any small nonlinearity in the amplifier causes an error in
lIIe feedback loop
to
appear at
lIIe
inverted input of
the
main ICop amp (UIOO). This means
the
main
Ie
output
(pin
6) will rise
above
its nonnal value
in an attempt
to
com:ct
the
problem
.
This
signal
is
lhen
responsible
for
raising
the
bias voltage
on
IC3 and
intwn activating
QI14
which
iUuminates E
102.
,,,.
,~
>w
""
''''
""
<~
Fig.
6.l
/OC
6·4 Circuit Theory
''''
,
"'"
1-_+-_I:F1ROR
sn.
'
N ""
·
10\1
6.10.
Signal
Presence
Indicator
E
101
is
lIIe
green front panel indlcatorwhich illuminates
at
any time
lIIe
output
voltage
reaches
I
volt
peak-peak
or
above.
RI31,
R132, 0107
and
QI15
are
Lhecomponents
directly involved in
the
above mentioned process.
~
El01
GN
R132
""
2W
0115
0107
~
NF'
Rl31
lDop
3.3K
Fig.
6.8
Signal Presence Indicator
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