IBM 5500 Operational, Installation, And Maintenance Manual page 107

such as 55 ohms one direction and 40-45 ohms the other direction.
Go to Step 5.
c. Readings low - 25-30 ohms, go to Step 6.
d. Readings = 0 ohms, go to Step 7.
e. Readings very low in both directions, such as 10 ohms, go to Step
8.
f. Readings = infinity, go to Step 9.
Step 4. The Cable and Termination metered correctly.
Your readings were 55 ohms on each center conductor regardless of the
polarity of the meter leads. Completing this step proves that the cable appears
to be OK and is properly terminated. Follow the cable and look at each
terminal on the cable. As you do this, check the following:
a. Verify the physical address of each device. Two devices with the
same address will keep one or both of these devices from working.
b. Twist and pull on each cable at each connector to see if the cable
will twist inside the connector. If the cable twists, the cable is not
assembled correctly and line checks and terminals can lose
communications with the AS/400. Most likely, the shield is not
placed over the braid clamp in the connector. The shield makes
enough contact for the meter reading but causes noise when an
operator kicks a cable or shifts a terminal around on a desk.
Correct assembly of the cable will correct this problem.
Note: A bad connector can be 3 or 4 terminals away from the failing
terminal.
c. Look for improper cabling practices such as improper use of "T"
connectors. "T" connectors are only used on devices with one port
such as 3179's. Some customers have tried to use them on devices
such as 5251's. Some customers are making their own "Ts". Be
aware that the length of the "T" cable cannot be over 12 inches.
d. Count the number of junctions in the cable. 11 is the maximum.
Wall plates can be a big offender. Some customers will wire every
office with a wall plate in anticipation of future growth. You can
end up with a cable that has 7 devices on it and 30-40 junctions.
This can cause intermittent and flaky problems.
e. Note where each terminal is plugged in. Each terminal requires a
grounded receptacle.
f. If you have not identified the problem, you may have to meter each
cable section for correct polarity and inspect each connector.
When metering IBM CS, you should measure 75 ohms between
each phase and ground, after you are past the Impedance Matching
Device at the system end.
Cold solder joints and pins not soldered to the conductors, will meter OK but
will cause intermittent problems. Do not disassemble a connector unless
necessary. Also look for pins lodged back in the connector and attempt to
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