IBM System/34 Maintenance Manual page 165

111-520 Cable Quality Check Procedure
If you understand the information in paragraphs 11 -500
through 11-515, you should now perform the cable
quality check. Set the knobs and switches on the
oscilloscope as shown in Figure 11-6. Then see Figure
11-7 and do the following:
1. Connect the T -connector to the B gate on the side
panel of the oscilloscope. (The output of the B
gate transmits a signal on the cable.)
2.
3.
4.
5.
10
Connect the coaxial cable from the channel 1 input
to one side of the T -conneGtor. If you have a
probe-tip-to-BNC-adapter (part 453199), use a
times-1 (X1) probe.
Connect a times-1 (X1) probe with a ground lead
and· alligator clips to the other side of the
T -connector.
Connect the alligator clips to the end of the cable
being checked as follows:
• Ground lead to shield
• Signal lead to phase V
Ensure that the other end of the cable being
checked is terminated. To do this do- one of the
following:
• Verify that a work station without the Cable
Thru feature is attached (cable is automatically -
terminated),
or
• Set the work station terminator switch to 1 on
work stations with the Cable Thru feature,
or
• Terminate the end of the cable with a resistor
assembly (part 7362344) as shown here:
Phase B
55n
Phase V
55n
Shield
6.
7.
8.
9.
11-520
If the oscilloscope is connected as instructed, you.
should now see a signal. If the signal shows that
the cable is good (no change in the signal level),
you may be checking only the first 91 meters (300
feet) of a longer cable. Therefore, change the B
time base from 0.1 microseconds to 0.2
microseconds, to 0.5 microseconds, and so on up
to 2 microseconds. The 2 microsecond setting
checks the maximum length cable of 1524 meters
(5000 feet), so it is not necessary to increase the
B time base to 5 microseconds.
If the transmitted signal changes at any of the B
time base settings, go to step 9.
If you see no change in the signal level when the
B time base is set to 2 microseconds, leave the B
time base on 2 microseconds and move the
alligator clips as follows:
• Ground lead to shield
• Signal lead to phase B
If the transmitted signal changes, go to step 9.
If you see no change in the signal level when the
B time base is set to 2 microseconds, leave the B
time base on 2 microseconds and move the
alligator clips as follows:
• Ground lead to phase V
• Signal lead to phase B
If the transmitted signal changes, go to step 9.
After you have checked all three possible
combinations (shield to phase V, shield to phase
B, and phase V to phase B) and there is still no
change of the transmitted signal, the cable is
good.
If there is a change of the transmitted signal,
move the B time base to a setting that will let you
calculate the distance to the bad cable. Use Figure
11-5 as an aid in calculating the distance, and
Figure 11 -8 as a reference.
Note: If for some reason you want to check the
length of a good cable, disconnect the cable from
the other end. The transmitted signal will show an
open circuit as shown in
e
or
G)
of Figure 11-8.