I have an installation where I need to interface (temporarily) POTS lines to a PBX with a PRI interface. To accomplish this, I have an Atlas 550 with an octal FXO card connected to the POTS lines and a PRI interface configured between the Atlas and the PBX. Based on review of the logs, the PRI interface seems to be working fine, but when I try to dial an outgoing call, the Atlas log shows "No Dialtone". A butt set connected to the POTS line works fine. Incoming calls are properly routed to the PBX but when answered all that's present is a horrible hum.
For testing, and to eliminate the PBX as the culprit, I've installed an FXS card in the 550 and connected the butt set to that. Outbound calls still get the "No Dialtone" as before, and inbound calls (now routed to the FXS port) get that same hum. In all cases, call audio can be heard in the background so I know it's present, but the noise overrides everything and makes the connection useless.
The POTS lines in question are not true POTS lines unfortunately, the are the output of a Motorola cable modem (SurfBoard SBV5322) providing the phone service. I'm hoping that's not the issue.
Do I have a bad FXO? (I haven't had a chance to try to swap it yet) Is there (hopefully) something I missed in configuration? Compatibility problem with the modem/POTS interface?
Offhand, it does sound like a bad FXO module. For the "hum" you can try adjusting the "Tx Gain" under MODULES, in the CONFIG for the FXO Module. The Tx gain will be the level transmitted to the PRI.
The "no dial tone" is what makes me believe the module may be bad. You can try adjusting the gain, but I doubt it will make a difference. If you can hear dial tone using a butt set on those lines, then dial tone is there.
You can also try moving the FXO module to a different slot in the chassis, but it doesn't look good.
Of course I don't have another FXO in stock to swap, but I think I'm going to have to find one. I did attempt gain adjustments, and while that seemed to have a minimal effect on the audio level of the actual call audio in the background of the noise, it didn't affect the noise at all and there was no change on the dial tone issue.
Dial tone (and in fact successful call function) is present on the lines in question with a butt set. I'll report back after I've had a chance to swap the card.