Service manual
and
power
is
applied
diractty
to
the
transformer.
4,9.3
Signal
Indlcatlan
4,8.3
Over
Voltage
Proteetion
Ul
El
serves
as
a
window
comparator
for
the
purpose
of
over line
voltage
cantro!, In the
event that
the
line
vslfags
sxceeds
10%
over
the
rated
line
voltage,
the
high
energy
power
supplies
are
disabled,
W7
%up-
plies
the
regulated
+
I
SV
to
pin
"I
of
U
1
B
and
serves
as
the
window
reference
level.
With
pin
10
in
csntrof
of
U1
D,
&he
output:
(pin
13)
has
a
logic
law
which
is
applied
across
033
and
014,
This
prevents
csndue-
tisn
and
allows
Q1
to
remain
on,
which
thus
allows
K2
to
remain
ensrgired
Resistors
W3,
W4,
R5
and
R6
serve
a$
a
resistor
drop-
ping
neWsrk
from
the
unregulated
+24V
supply
to
ground,
As
the
line
voltage
incraas~s,
the
unregulated
supply
will
increase,
The
voltage
iievsD
sn
the
wiper
of
R4
is
applied
to
Pin
1
1
(non-inverting
input).
When
the
Hevel
exceeds
%he
window
level
of
pin
-10,
the
circuit
switches
states,
This
allows
Dl
3
and
0
14
to
canduet,
incorporated
on
the
display
module are three
modes
ef signal
indication.
SB
(Signal
Presence
Bndicnfiow)
U
1
A
and
D3
serve
to
rectify the
amplifier
output
sig-
nal.
U1
B
takes
this
rectified signal
and
drives
the
LED,
E3,
which
illuminates
any
timg
there
is
signal
pre~ent
at
the
autpkdt of
the
amplifier
channel,
Dynamic
Range
With
the
switch
51
in
the
Dynamic
position,
this
recti-
fied
audio
signal
is
placed
on
the
invsrtin~
inputs
of
a
sequence
of
window
comparators.
This
signal
is
recti-
fied
but
unfiltered,
therefore
it
contains
ah@
peak
value
of
%he
audio
waveform,
U3C,
U3D,
USA,
U5B
and
U5B
serve
as
the
current
sources
for
the
five
Dynamic
Range
LEDs.
R29,
R3t
R33,
W35,
R37
and
R39
pro-
vide
a resistor
dropping
network
for
the
inverting
in-
puts
"l
athe
LED
drivers,
placing
a
logic
high
on
the
base
0%
01%
This,
iu
turn,
This
same
reclifisd
signal
is
placed
an
the
non-invert-
biases
off
Q
1
and
de-energizes
K2.
ing
i~lputs
via
the
filtering
Function
of
C3
and
the
op-
amp,
U1
C.
This
filtered
sigr~al
is
of
an
RMS
value,
With
4.9
Display
Circuitry
the
nan-inverting
inputs
receiving
the
RMS
value, and
the
inverting
inputs
receiving
th~
peak
value,
the
aut-
4.9.1
ilOC
pull
of
each
LED
comparator
equals
the
dynamic
U3A
and
U3B
serve
as a
voltage comparator
with
R13,
ranga
of
tha
signal,
R15
and
R'W
7s
the
r@sistor
dropping
newark.
Pin
'7'
has
a
window
level
of
+7V
and
pin
4
has
a
window
of
Output
Leved
-7V
U3A
and
U38
have
a
logic
high
which
turns
off
With
the
switch,
$1,
in
the
Level
positian,
the
peak
a1
and
the
10~
LEO
El,
when
ths
Signal
fro.cam
signal
is
still
placed
on
the
inverting
inputs
af
the
corn-
the
error
amp
appears,
the
7V
window
is
overcame
paratsr
drivers.
A
small
DC
level
is
piaced
ow
all
of
the
and
switches
the
state
of
U3A
and
U3B.
Q1
is
then
non-inverting inputs,
This DC
level
serves
as
a
cali-
biased
on
and
the
tOC
LED,
El,
iliuminates.
The
ca-
$rated
reference
far
comparatofs.
W78
calibrates
the
pacitor
C27
makes
sure
the
LED
is
lit
long enough
for
display
balance between
the
two
channels
sf
the
am-
the
human
eye
to
see
it.
plifier"
4,9,2
60EP
U1
B
on
the
display
module
is
the
curr@nt
source
far
the
OBEP
LED
E15,
Under
normas
operating
condi-
tions
pin
14
of
Uf
D
is
a
negative
vsitags.
This
allows
BY
ts
conduct
and
El5
to
illuw~inate.
As
the
ODEP
signal
drops
ts
the
point
wkiiere
OBfP
limiting
takes
Circuit
Theory
4-7