While we are talking about obscure faults, I was reminded of this one. We had a call from a customer with a BCM50. This one had an Optus Fusion line which was their main outgoing line because of the included calls plus they had 3 other Optus VoIP lines. The Fusion line was permanently forwarded to one of the VoIP lines that are set up in a hunt group.
The Fusion line comes in on its own cable pair whereas the VoIP comes out of an Integrated Access Device fed by 1 cable pair but capable of up to 6 analogue lines.
Intermittently, the Fusion line would not work properly and the customer said it had static on it. Since ADSL comes in on that line too it was possible that the filter was breaking down somehow but this was only a guess because I never managed to 'catch it in the act'. Replacing the ADSL filter seemed to fix the problem for a few months but then it recurred. I couldn't understand why the line should be 'eating' ADSL filters.
Optus were unable to fix the problem because they could never see any fault on the line.
Just once I did manage to catch it in the fault condition and it wasn't static. The phone system would seize the line OK but the dial tone was distorted and the speech quality was poor. A quick check of the line showed that the loop current was only about 10mA although the on-hook voltage was OK; the BCM50 requires at least 15mA to fully energise the line circuit. In the time the customer was there this fault was never fixed because we could never convince Optus to change the cable pair and the customer learnt to live with it. They have since moved premises and got a setup with another provider that they hate but are contracted for another 2 years so they are stuck with it, the high line cost and servicing costs.
ICS Technologies is located in Brisbane, Australia with national coverage on a variety of different phone systems.