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SERVICE INFORMATION
4.4.7 Differential
and Common
Mode Isolation
Tests
These tests check the leakage resistance (isolation) between
high (H) and low(L) (differential),
and from high and low
to guard (G) (common mode) of every row and column.
In general, the test is performed
by applying
a voltage
(low) across the terminals and then measuring the leakage
current. The isolation resistance is then calculated as R =
VII. In the following
procedure,
the Model 617 functions
as a voltage source and an ammeter. In the VII function,
the Model 6l7 internally
calculates the resistance from the
known
voltage
and current
levels
and displays
the
resistance value.
1. Turn the Model 707 off if it is on.
2. Connect the Model 617 to a quick-disconnect
terminal
block as shown in Figure 47. Do not connect the ter-
minal blocks to the matrix card at this time.
3. Place the matrix card in slot 1 of the Model 707, but
do not slide it all the way into the mainframe.
WARNING
The following steps use high voltage (1OOV). Be
sure to remove power from the circuit before
making connection
changes.
4. On the Model 6I7, select the 2pA range, and enable
zero check and zero correct in that order. Leave zero
correct enabled for the entire procedure.
5. On the Model 617, set the voltage source for +l03V, and
select the 200x4 current range. Make sure the voltage
source is still in standby.
6. Place the Model 617 in the V/I measurement
function
by pressing SHIFT OHMS.
7. With the Model 617 in standby, connect the pre-wired
terminal block to ROW A of the matrix card.
8. Feed the test leads through
the cable clamp of the
matrix card and push the card all the way into the
mainframe.
'lighten
the two spring loaded screws to
completely
mate the card with the backplane.
9. Turn
on
the Model 7W, but do not program any cross-
points to close. All crossuoints
must be open.
10. On the Model
617. disable zero check and press
OPERATE to source 1OOV.
11. After allowing
the reading on the Model 617 to settle,
verify that it is >lGO. This measurement is the leakage
resistance (isolation)
of ROW A.
12. Place the Model 617 in standby and enable zero check.
13. Progmn
the Model 707 to close crosspoint
Al.
14. On the Model
617, disable
zero check and press
OPERATE to source 1OOV.
15. After allowing
the reading on the Model 617 to settle,
verify that it is also >lGR. This measurement
checks
the isolation
of COLUMN
1.
16. Using Table 4-3 as a guide, repeat the basic procedure
of steps I2 through
I5 for the rest of the columns and
rows (test numbers 3 through
20 of the table).
17. Turn the Model 707 off and slide the matrix card out
of the mainframe
far enough
to gain access to the
prewired
terminal
block.
18. Remove the terminal
block from the matrix card and
rewire the it as shown in Figure 4-8.
19. Repeat steps 7 through
16 to check common
mode
isolation.
Table 4-3. Differential
and Common Mode Isolation
Test
Test No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Differential
or
Cmsspoints
Common
Mode
Test
Closed
ROW A
COLUMN
1
COLUMN
2
COLUMN
3
COLUMN
4
COLUMN
5
COLUMN
6
COLUMN
7
COLUMN
8
COLUMN
9
COLUMN
10
COLUMN
11
COLUMN
I2
ROW B
ROW C
ROW D
ROW E
ROW F
ROW G
ROW H
None
Al
A2
A3
A4
A5
A6
A7
A8
A9
Al0
All
Al2
Al and Bl
Al and Cl
Al and Dl
Al and El
Al and Fl
Al and Gl
Al and Hl
411
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