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The turn-off of the driver currents should be
before the terminator gate turn-off.
If
the current
is bei:r,ig turned off by the terminator gate, unwanted
noise in the array and bit failure may result (Figure
68). To correct this condition, replace the gate
cards (4196) or drivers (4904) that have the late
turn-offs. If the currents have different amplitudes
(read is twice the amplitude of write, or vice versa)
a bad gate terminator card (4889) is indicated.
Late Turn Off
Gates or Drivers
L1
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Lt
0
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FIGURE 68. CURRENT TURNED OFF BY TERMINATOR GATE
I
Sense Inhibit
The sense and inhibit circuits use the same blue and
white lines (Figure 69) from the logic boards, Al
and Bl, to the array,
The resistance of each leg of
the sense-inhibit line to ground should be about
7. 5 ohms. The resistance between the blue and white
wires at the output of the sense-inhibit card is about
15 ohms.
A
normal inhibit pulse at the output of the
inhibit driver card is like that in Figure 70. This
pulse is the same on either the blue or the white
wire.
*
M9=4927
M9A=8249
I
Cl Boord
FIGURE 69. BLUE-WHITE SENSE LINES, SENSE INHIBIT
....
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FIGURE 70. INHIBIT PULSE
When an open occurs in either leg of the sense-
inhibit lines, the output of the inhibit driver is like
that in Figure 71. Check continuity of the blue or
white wire from the sense-inhibit card on the Al or
Bl board to where the wire welds onto the B side of
the array.
If
continuity to the array is good, check
the small jumpers on the D side of the array for the
plane and segment that is bad, to see if the weld has
opened up.
If
the welds on the jumpers are good,
check the welds on the inhibit bus on the B side of
the array.
1l
T
J
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FIGURE 71. INHIBIT PULSE WITH OPEN LEG
If
a short to ground in either leg of the sense-
inhibit line occurs, or if the inhibit driver transistor
is shorted, the output of the inhibit driver is as
shown in Figure 72.
If
a sense-inhibit card has a
shorted inhibit transistor, that segment may run and
the other three segments may not run. Replacement
of the sense-inhibit card for the segment that is
running usually corrects the problem.
If
the output
of the inhibit driver card still resembles Figure 72,
use an ohmmeter to check the resistance of the blue
and white lines. If a short to ground exists on the
blue or white wire, pull the paddle card for that bit
and segment (see MD020) on the Cl board to isolate
it to the BSM or array.
Service Checks, Adjustment and Removal Pl'Ocedure
(3/71)
87
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