IBM 5500 Operational, Installation, And Maintenance Manual page 108

108
Chapter 6: Twinax Client Cabling Requirements and Problem Solving
correct the connector. Often a pin will push back into the connector when it is
mated to the female connector. If this happens, you will have sufficient
contact to get a good meter reading but the signal will not pass through the
connection dependably. If assembled correctly, the pins will not push back.
Go to Step 11.
Step 5. Cable termination metered correctly with the meter leads one
way; however, it measured low with the meter leads reversed.
An example of this situation would be 55 ohms in one direction and 40 ohms
the other direction. This condition indicates that you have a defective logic
element on one of the displays on the cable. Usually the defective device
works correctly but prevents other devices on the cable from coming on line.
If the devices are attached by "T" connectors, the fastest thing to do is leave
your meter on the cable with the bad reading displayed. Disconnect "T"
connectors one at a time from the devices until the reading returns to normal
(55 ohms). The disconnected device that allowed the reading to return to
normal is the defective unit. This failure normally displays on newer devices
such as 3180 and 3179's. If you suspect a device without a "T" connector, use
a splice connector to bypass it or break and terminate the cable as you
continue to meter the cable. Go to Step 11.
Step 6. The meter readings were low when termination was checked (25-
30 ohms).
This condition usually indicates double termination on the cable. Look for
termination switches at the devices with wrong setting and terminate jumpers
installed on the logic boards. Go to Step 11.
Step 7. The meter readings were 0 ohms.
This reading indicates that the phase conductors are shorted to the shield.
Break the cable into sections to determine the bad cable. Internal shorts can
look like a shorted cable. Go to Step 11.
Step 8. The readings were very low in both directions.
This reading indicates a defective device on the cable, such as a twinax
network station or a PC with 5250 emulation. Usually the failing device does
not come on line. Disconnect the "T" connector from the device and check if
the reading is normal. Go to Step 11.
Step 9. Infinity meter readings.
This reading indicates that the cable is un-terminated or is open. Check for the
following:
• Terminate switch setting on last device set to 1.
• Faulty "T" connector on last device (they fail to terminate at times).
• Plunger switch defective or stuck on devices with the plunger built into
port 2 of the device or the metal box type "T" connector.
Planning, Installation, and Maintenance Guide