We look after a number of phone systems as subcontractors to interstate companies. One of the phone systems we look after is an old Nortel BCM400 Release 3.7 (Windows NT -based…) and it has had an intermittently noisy reception phone for some time now. Like most intermittent faults it was very difficult to catch “in the act”. We were asked to attend site several months ago to investigate and it was working fine. These faults are normally as simple as curly cord getting stretched and causing the noise. In this case the curly cord appeared fine and no amount of manipulation of it could reproduce the fault. There was a suggestion that it might be the headset – it sounded OK too but was bypassed to prove it one way or the other. For the sake of thoroughness, I decided to change the wall socket the reception phone was plugged into and change the card it was connected to. The phone seemed to be quiet for a while afterwards but the crackles still came back.
This chassis had only recently been installed. It was supplied as a replacement chassis after the Base Function (processor) Tray had failed in the old one. The Melbourne-based company that looks after the customer flew the rebuilt one up with a tech to install it and during the refurbishment process the power supply and hard drive had been replaced. Clutching at straws it was decided to replace the power supply again in case it was inducing noise into the system although it didn’t seem to be occurring on other phones but the customer couldn’t be 100% sure.
Due to the clutter in the rack the power supply cannot be replaced in situ so the whole chassis had to be removed – obviously an after hours job. When I arrived I checked the reception phone for noise and manipulated the cords again – just to be sure. It was dead quiet but I did notice that the headset had been connected again. While waiting for the business to close I was able to connect up the lift phone to an analogue adapter as it was a straight analogue line that had been cut off by NBN.
After the power supply was changed the BCM400 was booted up and stabilised after about 20 minutes so I made a call to Melbourne from the reception phone as it is the closest phone to the PABX room and it was crackly! The T7316e phones need a mechanical lifter to allow remote answering with the headset as they are not Electronic Hook Switch compatible and this requires an adapter cable that goes from the phone to the headset base. The handpiece also plugs into this cable. I started fiddling with this adapter cable and finally was able to reproduce the fault.
When sitting flat as pictured below there was no noise and no amount of manipulation could induce it.
As soon as the little interface box was turned 90 degrees so the socket was facing the desk the noise was very bad.
I had a few of the cables in stock in the office from other headset installs on phones that use an Electronic Hook Switch so I simply posted a replacement out.