Steps To Check Cable Using A Current Probe - IBM 5500 Operational, Installation, And Maintenance Manual

Steps to Check Cable Using a Current Probe

• Meter at last device to verify termination. If OK, find the open in the
cable. If you read 110 ohms from conductor to conductor and infinity
from conductors to shield, the shield is open. Otherwise, one or both
conductors could be open or the entire cable may be open (the cable might
have been cut into or is disconnected from a device splice joint). Go to
Step 11.
Step 10. Outdoor cable with station protectors installed.
Be aware that you can not meter through the station protectors. IBM
recommends that you replace the station protectors with splice joints. Return
to Step 2 and after correct completion, try operating the line without the
station protectors.
Caution: Do not bypass or leave the station protectors out of the line if an
electrical storm is pending.
If the line works OK without the station protectors, check for the following.
• A defective station protector.
• One or both protectors installed backwards. The outdoor cable must go to
the end of the station protector that has the ground wire.
• Excessive AC current flow on the shield of the cable caused by a
difference in ground potential between the buildings. No grounds or
missing grounds on the station protectors.
Step 11. Problem not resolved.
Return to Step 2 and re-check the path.
If the problem persists, use a scope to perform the "Advanced Time Domain
Relfectometry (TDR) Procedure" on page 113.
Note: While scoping the cable, have an assistant shake the cables at each
device. Look for momentary shorts and or opens to appear.
This section is for qualified maintenance personnel who service the 5500
Control Unit and twinax cabling installations. Refer to the Safety Information
Booklet, S021-0030.
You can perform the following cable check without interruption. This
procedure will find open shields on twinax cables and can work with any type
of oscilloscope (the oscilloscope setup, below, is for a Techtronics 475). The
system must be in a normal operating mode (for example, sign on screens on
the displays or customer actively using the system).
Step 1. Locate the following required parts:
• Oscilloscope
• Current probe with the following characteristics:
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