•
set
at
about
+3.7
V.
The
input
intensify
signal must
go
more
negative than
+3.7
V
before
it
controls
the
blanking
amplifier
output.
All
the
controlling
input signals pass through common
base
a
m
p
l
i
f
ie
r
OS15. which
provides
a
low
Input
im
pedance
and
isolation
from the impedance.matching and
bias-setting
transistor
OS20.
A
current flow
of
ap
proximately 5 mA
through
OS20
turns the
crt
beam
off.
while
the
front-panel set intenSity
causes a
current
of
about
1
mA
through
the
transistor.
If
the
c
u
r
r
e
n
t
through
OS20
is
a
b
o
u
t
0.3
mAo
the
crt
beam
will
be
intensified.
High-Voltage Regulator
High-Voltage Aegulator.
OS60. OS
55
.
OS50
and
US60
with their
as
s
oc
i
a
t
ed
components
p
r
o
v
id
e the
regulation
and the drive
to
energize a
resonant
transformer TSOO.
T850
a
l
l
ow
s
TSOO
pr
im
ary
winding (pins
4
and 5)
to
move
sinusoidally while allowing
O
S
5
5
and
0850 to
function as
saturating
switches.
High-Voltage Aegulatlon.
R
e
f
e
r
to
Fig.
3-2
during
the
following
discussion.
Regulation
is
accomplished
by
sampling the
-2
kV across
v
o
l
t
a
g
e
divider R893C-RS930
and
c
o
m
pa
r
i
n
g it
to
a
+20.0
V
reference
supply.
The
ju
n
c
t
i
o
n of
R893C·RS930
as well
as
pin
3
of
US60.
is
nominally
0 V.
If
the
-2 kV
supply
sh
o
u
l
d
become
less
negative. the
junction
of
R893C-RS930
and
hence pin
3 of
U860
becomes
more positive.
causi
ng
the output (pin 6) of
U860
to
go
positive.
The
o
ut
p
u
t
of
U860
going
positive
results
in increased
charging
c
u
r
r
e
n
t
for
C857.
which will
cause
0855
to conduct longer
during each cycle.
thereby
increasing
the
average current to
T800
and
T850.
As
OS55
begins
to conduct.
T850
allows
It
to
saturate
while
prov
i
d
in
g
positive feedback
from
its one.turn winding to
ensure
that
saturation
will
continue until pin
5 of TSOO is
at
its
most
negative
v
o
l
t
a
g
e
.
During
the conduction
of
OS55,
C854
is
charging,
then
at
the
time
pin
5
of
T800
is at
its
most
negative voltage.
CS54
starts
dischargi
ng,
cutti
ng
off
CRS55
and
t
u
r
ni
n
g
on
CR853
to
provide
base current
to
OS60. 086O's conduction
re
d
u
c
e
s the b
a
se current of
OS55,
thus
c
a
u
s
i
n
g
its
c
oll
e
ct
o
r
to
go
more
positive. The
turning
off
of
0855
is
speeded
up by the
action
ot T
S
5
0
with
its one.turn
winding.
The
current
t
h
r
o
u
g
h
T850
and
the
energy
s
t
or
ed within
the
coil
now flows
through
T800
via
0850
and CRSSO.
OSSO
remains
turned
on
until T850
has
been
completely
discharged
.
With
0 V
across
0850
base-emitter. the
p
r
i
m
a
ry
of
TSOO
may
now
swing more
positive than the
input
supply
v
o
l
t
a
g
e
.
@MAY 1980
Theory of
Operatlon-SC
502
Pin 5 of T800
DV
PI" 6 01 TBOD
1878-33
Fig. �2. nme
rel.lonshlp
of waveforms. thr"
points
In the
hlgh-volt-ve regul.or.
The
high
0
of
TSOO c
a
u
s
e
s
its
voltages
to
vary
si nusoidally,
thus
setting
conditions
for
conducti
on
agai
n.
During the
time
that
OS55
was not
conducting.
U860
was
charging
CS57
to
a voltage
level
which
when
combined
with
voltage of the
one.turn
feedback
wi
ndi
ng of TS50
will
again
cause
0855
to conduct. Initially
at
instrument
turn
on. the
reference
supply
v
o
l
ta
g
e
is
allowed
to
move
p
o
s
it
i
ve slowly,
d
e
p
endi
n
g
upon
the
charging rate
of
CS70
(
w
h
i
c
h
is
c
o
n
t
r
o
ll
ed
by RSSO).
Once
the
voltage
at pin
Fll
b
ec
o
m
es more
positive
than
+20
V. CRS62
conducts
and
t
h
e
reference supply
is
held
as
a constant
+20.6 V. If
a
short
should
occur
to
the
TSOO
secondary,
the voltage
at
pin
Fl1
will move t
o
w
a
r
d
zero,
thereby
reducing
the
reference voltage and
consequently the
transform
er
drive.
If
a
T
S
OO
secondary
wi
n
d
i
n
g
short
remains
for
a
time. FSOO
will blow
to
protect
0855. If
the
R893C-RS93D
voltage
divider or
the
r
e
g
u
l
a
t
o
r
circuit
should
fail
R855
and
R857
will turn
CRS56
on
to
remove the base d
r
i
v
e from
OS55
vi a
0860.
High-Voltage Outputs
The
secondary winding
of
TSOO
provides
the
negative
and
positive
accelerating
p
o
tenti
a
l
for
the crt. the bias
voltage
for
the
c
o
n
t
r
o
l
grid
and
heater
voltage
for
the
crt.
Positive accelerating
voltage
for
t
h
e
crt
screen
is
supplied
by
v
o
l
t
a
g
e
trlpler U850.
The
applied voltage to
the input of
USSO
from
the
TSOO
s
ec
o
n
d
a
r
y
winding
is
about
3.3
kV peak.
The
voltage for the
crt
directly heated
cathode is also
obtained
from the
T800
secondary
win
ding.
CRSS1
half-wave rectifies
the
transformer
output
a
n
d
supplies the -2 kV to the
crt
cathode .
3·7
...
Summary of Contents for SC 502
Page 1: ...SC 502 OSCILLOSCOPE ...
Page 2: ......
Page 9: ...SC 502 1878 1 The SC 502 Oscilloscope xi REV APR 1982 ...
Page 10: ...Verso Filler Page z z ...
Page 32: ...Verso Filler Page z z ...
Page 34: ...Verso Filler Page z z ...
Page 63: ...Section 6 SC 502 OPTIONS There are no options available at this time REV A APR 1980 6 1 ...
Page 84: ...Beam R873 C473 Ext Bal R535 CH 1 Vert Po R335 CH 2 Vert Pos R394 ADJUSTft TP980 5 ...
Page 125: ...REV MAR 1 984 ...
Page 126: ...SC 502 m m o ...
