IBM 5500-01E, Operational, Installation, And Maintenance Manual

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If multiple reflections are displayed as shown in Figure 49, the fault is less
than 50 m (164 ft) from your end of the cable, or the B-time base is not set
correctly.
Figure 49: Multiple Reflections
Increase the B-time/div from 0.1 to 0.2 or higher until a reflection displays;
or, decrease the B-time/div to 0.05 so only a single reflection displays (as
shown in Figure 50).
Figure 50: Single Reflection
When the reflection is displayed, you must short the opposite end of the cable.
If the displayed reflection changes by 180 degrees, you are seeing the other
end of the cable. If the displayed signal does not change when the opposite
end is shorted, the signal reflection is caused by a fault in the cable.
Consider the following when you perform the tests:
• To determine the length of the cable, IBM recommends that you start with
the remote end of the cable open (unplugged).
• You can use 110 Ohms resistor or a resistor assembly (IBM P/N 7362344)
to terminate the line, or you can terminate the line by plugging the cable
into a workstation and setting the workstation terminator switch to 1.
• You can connect short cable segments up to a maximum length of 1524 m
(5000 ft).
55E1I026
B-sweep time /div=0.1 µs/div
55E1I027