IBM System/34 Maintenance Manual page 163

11-510
Cable Checking Introduction
If you understand the cable quality check, go to
paragraph 11-520 and perform the check. However, if
you do not understand this check, it is important that
you carefully read all of the information through
paragraph 11-515. You can use this information as an
introduction to cable checking with the use of an
oscilloscope. Additional information can be found in
An
Oscilloscope Measurement Procedure for Twisted and
Coax Cables, 5226-3913.
11-513 Typical Signals
When you use the oscilloscope to make the cable
quality check, you will probably see a scope display
similar to the following figure. This figure shows the
transmitted signal for a normal cable, and the change in
signal level that occurs if a cable has an open or short
circuit.
Transmitted
Signal
Open Circuit Cable
Normal
Cable
Notice that for an open circuit cable the transmitted
signal moves upward; for a shorted circuit cable the
transmitted signal moves downward. However, for a
good cable, there is usually a small change in the
transmitted signal level, or no change at all. Small
changes (less than
10
percent of the transmitted signal
level) are normal and they are probably caused by a
cable-to-cable connection or by a connector on a work
station.
Note: A change of more than 10 percent of the
transmitted signal level usually indicates a cable
problem.
..........
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(Properly Terminated)
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......... .
Short Circuit Cable
8
11-510
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