IBM System/36 Maintenance Information Manual page 94

• For more information on the IBM Cabling System, see the IBM Cabling System Planning and Installation
Guide, GA27-3361, and the IBM Cabling System Problem Determination Guide for Twinaxial
Applications, GA21-9491.
The cable signal quality check determines if a failure is present in the cable, the cable connectors, or an
attached work station. This test sends a signal down the cable, using the square wave from the B-gate output
on the oscilloscope. Signal paths up to a maximum of 1524 meters (5000 feet) can be checked.
It is normal for a surge suppressor to cause a glitch of the signal. See sample oscilloscope signals lJand
m.
See "712 Sample Oscilloscope Signals" on page 7-10.
Defective Cables
If the cable is terminated by the correct load impedance, all the power of the transmitted signal is used by the
terminating impedance.
If there is a cable failure that changes the impedance of the cable, part of the signal is returned to the signal
source as a reflection.
A short circuit in the cable causes the impedance to be lower than normal. This causes a decrease in the
amplitude of the signal.
An open circuit in the cable causes the impedance to be higher than normal. This causes an increase in the
amplitude of the signal.
I
I
I"
Transmitted
Signal
I Distance to
Impedance Change
I
I
I
I
I
I
I
I
.1
,.----- Open Cable
I
I
I
I
I
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I
Normal Cable
(properly terminated)
'------ Shorted Cable
R36B116"()
Test Equipment Needed
To perform the cable signal quality check, you should have the following (or similar) equipment:
• One Tektronix 453, 454, or 475 oscilloscope. (This procedure uses the 475 oscilloscope.)
• One BNC T-connector (part 1650289).
• One probe-tip-to-BNC adapter (part 453199).
• One coaxial cable with a BNC end and alligator clips (part 1650290), or a BNC-to-banana-plug adapter
and multimeter leads.
• One times 1 (Xl) probe (a times 10 (XIO) probe may be used by changing the vertical input setting).
• Cable termination on the cable being checked. See step 5. of the setup procedure that follows.
7-4
5363 Maintenance Information