Connecting the
39G
183
to the circuit
The
39G183
rna)' be used
in
either of Iwo
.....
ays
to make circuit
connections:
....
ith
a
retractable
hook tip,
or
....
ith
a needle-type
connector. To use the
retractable
tip, simply pull back on the
collar (see Fig.
16)
to expose the connecting hook. Slip the hook
O\'er
the component lead
or
test point, and N!lease the collar,
'The
sleeve
....
'ill thenslide fON'ard to hold the probe
in
place.
-"-
~.-
...
_-..
.....
--
...
-
.....
_-.....,
"
~
:1
"'·':C"ltl
.~."
MOlt
"U':)"I:'
a"·
,,_
"ts
OIVlSIO~
• •
,
be routed separately from the signal used
to
drive the CRT.
digital
peak-to-peak function, and digital frequency function.
If
all signals had been routed
in
one path, it
.....
ould have been
necessary to have the
11\'PUT
COUPLING switch
in
the "DC"'
position to
measure
DC
voltage \\ith the digital display. This.
however. was not convenient because most waveform measure-
ments
are
easier to make with the CRT input
in
the
AC
coupled
mode.
Simply connecting
the
DC
lead to the scope probe ahead
of
the
scope
isolation network, hov.·e\·er. leads
to
loading problems. TIle
DC
lead acts like a capacitor placed
in
parallel y,ith the isolated
scope probe. causing problems.
in
high impedance
or
high
frequenc~'
circuits. The solution was to add a second isolation
network inside the probe_ The
39G183
probeserves as both a
10:
1
DC
dhider
and a
10:
1 AC divider. The
DC
lead
is
resistively
isolated from the
circuit, just like the
AC
path.
The
input impedance of the CRT circuits
at
the input jack
is
1
megohm when
DC
coupled,
or
2megohms when
AC
coupled. The
impedance of the
DC
input is
1.5
megohms.
The
series isolation
inside
the probe increases both \'alues to ten times
the
direct
input.
or
10
megohms for the
AC
path and
15
megohms for the
DC
path_
The
t\1:0
measuring paths
are
usuall)' in parallel for a
total
DC
impedance of about 6 megohms. While this is a some-
what lower impedance than most scopes, there
are
\·el')·
fe'llo·
circuits affected by the slightly
1000·er
impedance_
If
DC
loading
is
ever a problem, simply disconnect the
DCV
I~
lead from the
SC61.
The input impedance
....
ith
the
DC
path disconnected is
10
meji!ohms
.....
hen
DC
coupled
or
11
megohms
.....
hen AC coupled.
Connecting
the
39Gl83 to
the
SC61
The
separate
AC and
DC
paths require two connectors for each
probe.
Connecl the
Bl'."C
connector flrst to hold the assembly
in
placewhile connecting the
DCV
IN
lead.
Fig, 16 - Pulling back
on
the coUar
exposes
the metal
hook that
Is
connected to the circuit.
Fig.
17 - Unscrew the probe tip to expose a sharpenea
steel probing tip.
The pointed tip
is
exposed by unscre
....
ing
and removing the
retractable tip. The tip
is
made of hardened steel to insure solid
connections
to
circuits that
may
have an oxide coating that
prevents reliable electricalcontact.
CHANNEL
B
I.'
•...
c,
Connect the probe
.....
ith the blue ring on each end to the channel
A input
10
lell
.....
hich probe is
.....
hich \\ithout tracing the
....
ires
from the probe back to the
SCSI.
The probes
.....
ork equally well if
the
blue-coded probe
is
connected
to
channel B, but you lose the
convenience
of
color-eoded probes,
INPUT
COUPLING
DC
~
AC
The
SC61
includes a special
DC
\'oltage probe in addition to the
t
.....
039G18310
.....
-eapacity probes. The
39G157
DCV
probecontains
the
10:
1
di\;der
resislor needed for
c1i.rect
readings. Unplug the
39G183
DC\'
IN
connector from channel A
or
B and replace it
....
ith
the
39G157
plug
.....
hen you
.....
ant
to make
DC
measurements
.....
ithout using the
39G183
probes.
Press
the channel A
or
B DC\'
DIGITAL READOliT button for the channel that
has
the
DCY
probeconnected to read the \'oltage applied to the
39G157
input.
Fig, 14 -
The
small banana plug must be connected to
the
DCV
IN
jack to read
DC
vaNs
through the fow-capacity
probe,
17
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