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SERVICE INFORMATION
13. Close crosspoint
Cl by using the front panel controls
of the Model 707.
14. Disable zero check, and allow the reading to settle.
15. Verify that the offset current reading is i 2OpA.
16. Enable zero check, then open the crosspoint presently
closed.
17. Repeat steps 12 through
16 for rows D through H. The
electrometer
should
be connected
to the row being
tested, and only one crosspoint
must be closed at a
time. The offset current for each crosspoint should be
<ZOpA.
43.5 Path Isolation
Verification
The procedure
for verifying
path isolation
is discussed
below. Should the card fail any of the tests, clean it using
the procedures
outlined
in paragraph
4.2. If rows C
through F still fail, the problem may lie in contamination
of the mainframe
backplane.
NOTE
If the path isolation for specific rows is below stan-
dards, test the associated rows or columns with
the card removed from the mainframe. (Of course,
-
it will not be possible to close crosspoints with the
card removed.)
If rows C-F pass with
the card
removed
but fail with
the card installed,
the
backplane in the mainframe may require cleaning.
See the Model 707 Instruction
Manual.
Recommended
Equipment
l
Model 707 Switching
Matrix
l
Model 617 Electrometer
l
Model 7078-TRX-3 triaxial
cable
l
Unterminated
3-slot triaxial
cable (cut connector
off
7078-TRX-3)
l
Banana pl;g
(Keithley
part #BG-10-2)
l
#16-l8AWG insulated
stranded wire (6 in. length)
Test Connections
Figure 4-4 shows the test connections
for the path isola-
tion tests. One row being tested is to be connected to the
Model 617 Electrometer input through a Model 6172 2-slot
female to 3-lug male triaxial adapter. The other row is to
be connected to the voltage source HI terminal
using a
specially prepared 3-slot triax-to-banana
plug cable, the
construction
of which is shown in Figure 4-5. Note that
both the inner shield and the center conductor
are to be
connected to the banana plug as shown.
COM and the LO terminal
of the electrometer
voltage
source must be connected together as shown. Also, the
ground link between COM and chassis must be removed,
and the Model 617 guard must be turned off for current
measurements.
Procedure
WARNING
Hazardous
voltage
from the electrometer
voltage source will be used in the following
steps. Take care not to contact live circuits,
which could cause personal injury or death.
NOTE
The following
procedure must be performed at an
ambient
temperature
of 23OC and at a relative
humidity
of less than 60%.
1. Turn on the Model 617 and allow it to warm up for two
hours for rated accuracy.
2. With the mainframe power turned off, plug the Model
7U72 into slot 1 of the mainframe. Remove all other cards
from the mainframe,
and install the slot covers.
3. After the prescribed warm up period, select the Model
617 amps function,
and enable zero check. Select the
2pA range, and zero correct the instrument.
4. Connect the Model 617 to rows A and B of the matrix
card, as shown in Figure 4-4.
5. Program the Model 617 voltage source for a value of
+lOOV, but do not yet turn on the voltage source
output.
6. Close crosspoints
Al and B2 by using the switching
matrix front panel controls.
Z With the Model 617 in amps, enable suppress after the
reading has settled.
8. Turn on the Model
617 voltage source output,
and
enable the VII ohms function
on the electrometer.
9. After the reading has settled, verify that the resistance
is >loTQ (lO'%).
10. Turn off the voltage source, and enable zero check.
Disable suppress, and select the amps function
on the
electrometer.
11. Open crosspoints Al and 82, and close crosspoints A3
and B4.
12. Repeat steps 7 through
11 for A3 and 84.
X3. Repeat steps 7 through
12 for crosspoint pairs A5 and
86, A7 and 88, A9 and BlO, and All
and 812.
14. Disconnect
the electrometer from rows A and B, and
connect it instead to rows C and D.
4-5
I
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