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2.
Run the
"al~
ones" test and adjust your scope
to the same scale as Figure 55.
3. Make sure the strobe falls 120
±
10 nanosec-
onds prior to the peak of the output signal and then
run a shmoo curve.
4. If the shmoo curve picks or drops bits before
it
makes the established limits, re-adjust the 5-
nanosecond delay tap to obtain the best shmoo for
both "all ones" and "all zeros."
5. Realize that if the strobe is set near point b
(Figure 55) the tendency is to pick bits and
if
the
strobe is set near point c, the tendency is to drop
bits.
6. For strobe Buse pin B1C2J09 (ALD MC081)
as a test point and repeat steps 2-5.
12o:t1ons_l
d
I
Approx
I .6v
Gnd _ _ _ ' _ _ _ _ _
o.
9 ±_._iv _ _ _ _
l~-
r
I
FIGURE 55. MAIN STORAGE STROBE
Checking MS Drivers and Terminating Diodes
Much time is lost in machine storage areas in ob-
serving waveforms with a voltage probe. Remember
that a line with little or no current on it will appear
the same as a good line
if
you use a voltage probe.
If
you suspect blown drivers or terminating diodes,
use a current probe.
1. Drop de power on the machine.
2.
Locate the card whose outputs you want to
scope and extend it with a card extender.
3. On the extender, locate the line you want to
scope, remove the short jumper wire (Figure 56),
and replace it with a longer wire.
This will give
you a sufficient loop with which to hang the current
probe.
4. Bring up power and observe the pulse.
5. Always drop de power when changing or
removing driver, or the jumper wire on extended
drivers.
D
Pins of
Extender
Card Plugs ;ere]
FIGURE 56. CARD EXTENDER JUMPER WIRE
Delay Line Clock
Pins of
Extender
Longer Wire
for Current
Probes
Timings taker). from the AlC6 delay line (Figure 57)
are used to set timing latches. Timings from the
AlF6 delay line are used to reset timing latches.
Changing the set master reset timing on the AlC6
card also changes all timings taken from the AlF6
card Timings from the A1B6 delay line are used to
set the strobe turn-ons.
+Allow Sel
+Gate Sel
+ Storage Sel
~--~
MAOll
Delay
Line
Dvr
Reset Master Request
Set Master Reset
Master
Reset
Delay
1 - - - - - l
Line
Dvr
MA021
MA031
FIGURE 57. DElAY LINE CLOCK
25 ns
Taps
135
SS
5 ns
Taps
Service Checks, Adjustment and Removal Procedure
(3/71)
83
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