Communication failures typically fall in to 2 categories:
[1] bad interconnecting wiring
[2] board faults
If you’re not using Belden 8162 or 8163, you run the risk of causing a communications problem that gets worse with time.
The CRU talks RS232 which then routes to a converter (RS232 to RS422) before the signal leaves the CRU. The transceiver receives the RS422 directly without a converter.
Here is the order of typical failures:
[1] RS232/RS422 converter in the CRU
[2] IO Plexor
[3] CPU board in the CRU
Call for more details.