Definity G3- Ground Hum on CO Trunks and Analog Extensions

[grs033]

Good morning...

I maintain on the side a legacy Definity G3V6i Prologix switch for a friend's business (yes... old school, I know. But they like it and it still works well for them...). I'm good enough at Definity to get by, but I'm more of a Nortel guy. So I'm turning to you guys for help...

Around two weeks ago, there was a major wind storm in this area which caused widespread power outages. This occurred on a Sunday morning. There clearly was a decent surge that occurred due to the power outage because they lost two surge protector power strips, one pc, an employee's personal space heater (which was off at the time), a Keurig coffee brewer and microwave in their break room. I opened all the failed electronics and found the MOVs blown in each item.

Despite the switch and Intuity Audix not being protected by surge suppressors, they both survived. However, since this event, a 63 hz square wave hum is heard on the CO trunks and analog extensions in the building. Digital sets (a mixture of 8410Ds and 8434DXs) do not have the hum. They have 3 POTS lines in use; two provided by Spectrum via an ATA, and one a copper line for faxes provided by Verizon. I used a butt set to verify that the hum is not present on the lines from Spectrum, and no hum is present on the line from the network interface of Verizon.

I read an old thread which suggested moving the chassis ground of the switch to the telco ground to avoid a difference in ground potential which might cause the hum. No luck. I don't have a spare CO Trunk card (they have a TN747B V26), but I did move the lines to spare ports with no change in the hum. I did have a spare TN742 V19, and changed that out; but the hum is still present on the analog extensions when calling a digital extension. Curious, though, is that the analog lines going to Intuity Audix sound clean; and that uses 4 analog ports with in-band signaling. All other functions of the system (announcements, hold music, etc.) all sound clean.

Does anyone have any guidance on where to start looking to cure this problem? I've run out of ideas.

 

[joe2938]

Start 1st by installing a new co trunk card and retest, start ruling things out. Also a reboot of the pbx may be in order.

 

[Sean655]

Maybe plug the definity into a power conditioner, just thinking that there could still be some power issue coming into the building.

If the issue persists after swapping other parts (cards, bus terminators) maybe try another cabinet. If you don't have one perhaps a local avaya reseller has one to sell.

 

[grs033]

Joe,

One of the first things I did was performing a Reboot System 4. I would be inclined to get a new CO Trunk Card, but the hum is also occurring on analog extensions. So I'm thinking it must be a deeper issue.

 

[joe2938]

Any alarms or errors on the system, run the test environment command, also did you replace the analog cards as well?

 

[grs033]

Sean,

I was thinking of also having them get a battery backup to keep things running until the generator transfers over. That could help condition the power as well.

Joe,

No alarms except for an unplugged extension (which is on purpose). I ran tests on the CO Trunk board and replaced the Analog Line card already. Nothing thus far has helped...

 

[joe2938]

I'm wondering if the analog phones got damaged as well.

 

[DAVIDPAYNE]

Have you checked your grounding?

 

[grs033]

Joe,

I used the butt set to test the analog lines and verified that the sets themselves are fine. I heard the hum on the butt set.

David,

Yes. As one of my early troubleshooting steps, I moved the cabinet’s chassis ground from the AC wiring to the telco ground to eliminate difference in potential as being a cause. Nothing changed with the hum when I moved the ground over. The ground cable in use is #10 THHN with a bug (split nut) on the copper cable the telco is bonded to.

 

[DAVIDPAYNE]

I have not worked on A Prologic in a long time. But they were a good option for smaller offices, at least at the time.
If you have check the lines coming in and found no humm, then i would bet the system is damaged. the issue here is you have no spare parts. But from the sound of it, your office took a nice power spike. My 1st guess would be the power supple is damaged. But I also would not rule out the building power. If you can change out the which power circuit you use to power the system. Or as you stated, put a UPS on it to help filter out noise. You might also try to reset the breaker on that power circuit.