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FIGURE 64. OPEN X DRIVE LINE
like that in Figure 65. With an open, the voltage
indication resembles that in Figure 66.
With a short, the indication in Figure 65 appears
on the line selected and also on the line shorted
to
it.
The shorted lines should be adjacent drive lines.
Once the shorted lines have been isolated, take an
ohmmeter and walk across the array on the shorted
lines until the least resistance is reached. When a
resistance of nearly zero is reached, examine the
area for the cause of the short. Look for drive line
pins bent and touching or a metal chip between the
pins. A chip may wedge under the rubber seal
between planes.
If
the shorted lines are not adjacent,
replace the gate cards (4196) associated with the
shorted lines (see MD030L
An example of an open drive line is shown in Figure
66. To locate an open in the array, use a voltage
probe and step across the planes of the array on the
open line. When the open is passed, the indication
in Figure 66 reverses--positive becomes negative,
and negative becomes positive. In the area of the
open, check the drive line welds for secure bonding.
Remember that the drive lines zigzag across the
array, and the weld may be on either side of the
array.
If
the welds appear to be good, use an ohm-
meter to isolate the open.
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FIGURE 65. POSSIBLE SHORTED DRIVE LINE
86
(3/71)
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FIGURE 66. POSSIBLE OPEN DRIVE LINE
I
Drive Line Shorted to Ground
A current indication such as that in Figure 67
usually indicates that a drive line is shorted to
ground.
If
the X current is bad, check the inhibit
resistor assembly on the B-side of the array to
make sure
it
is not shorted against the X drive lines.
Three standoffs are located on the B and D side of
the array and one standoff on the A and C side be-
tween the Dl board and the front frame casting.
If
one or more of the yellow and black wires that go
to the pins on the array are pinched between the
standoffs, the indication is like that in Figure 6 7.
A shorted limiter on the gate card (4196) can cause
the same indication.
If
a gate card might be the
cause of the trouble, watch the defective current and
pull the gate cards one at a time.
~hen
the defec-
tive gate card is pulled, the current is similar
to
normal current with an open line.
If
one of the orange drive lines from the driver
card (4904) on the Bl board to the array interface is
shorted to ground, or if a transistor in the driver
card (4904) is shorted, the indication resembles that in
Figure 67. A defective gate clamp card (3583) gives
a similar indication.
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FIGURE 67. DRIVE LINE SHORTED TO GROUND
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