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Troubleshooting Hubs and MSAUs
If you experience problems with a hub-based LAN, such as a 10BASE-T network, you often can isolate the problem by disconnecting the attached workstations one at a time. If removing one of the workstations eliminates the problem, the trouble may be caused by that workstation or its associated cable length. If removing each of the workstations doesn’t solve the problem, the fault may lie with the hub. Check the easy components first, such as ports, switches, and connectors. Then use a different hub (if you have it) and see if the problem persists. If your hub doesn’t work properly, call the manufacturer.

If you’re troubleshooting a Token Ring network, make sure the cables are connected properly to the MSAUs, with ring-out ports connecting to the ring-in ports throughout the ring. If you suspect the MSAU, isolate it by changing the ring-in and ring-out cables to bypass the MSAU. If the ring is now functional again, consider replacing the MSAU. In addition, you might find that if your network has MSAUs from more than one manufacturer, they are not wholly compatible. Impedance and other electrical characteristics can show slight differences between manufacturers, causing intermittent network problems. Some MSAUs (other than the 8228) are active and require a power supply. These MSAUs fail if they have a blown fuse or a bad power source. Your problem also might result from a misconfigured MSAU port. MSAU ports might need to be reinitialized with the setup tool. Removing drop cables and reinitializing each MSAU port is a quick fix that is useful on relatively small Token Ring networks.

Isolating problems with patch cables, adapter cables, and MSAUs is easier to do if you have a current log of your network’s physical design. After you narrow down the problem, you can isolate potential problem areas from the rest of the network and then use a cable tester to find the actual problem.