atcomsystems.ca/forum Forums Other TDM Phone Systems Vertical Telephones & Systems SBX and Comcast dialtone, incoming calls drop

Customer has an SBX and when he had 3 AT&T POTS lines, the system worked fine. Switched to Comcast yesterday and the customer cannot make or receive calls. On incoming calls, the call can be answered, but the call drops after a couple of seconds. On outgoing calls, the customer now gets fast busy when trying to dial an outside line. Has anyone encountered anything like this? The previous installer mentioned to the customer that there was a single setting that could be changed in the SBX, but didn't elaborate. The wiring from the Comcast box is simple 2-wire with RJ11 ends on the ends plugged into the Comcast box and the other ends are punched down on a 110 block in the same position that the AT&T lines were punched down. Other than that, none of the wiring on the 110 block has been changed from how it was originally set up with AT&T lines. Wiring from the 110 block goes through the Vertical "octopus" cable and the wires for the 3 CO lines are terminated in RJ11 ends and plugged into the LCOB card.

I have checked and there is dialtone all the way through the octopus cable and I can make calls with the butt set. I have checked voltage of the lines and they shows -48.5 VDC. I have tried defining the CO lines as "PBX" rather than "Normal," and have even tried defining the CO lines as ISDN. I haven't yet found a single setting that could be changed that makes the system work.

I'd appreciate any suggestions.

Everything worked until they switch to Comcast. I wonder where the trouble may be? This is really a no brainer. The customer has a choice to make. Service that works. Or cheaper service that doesn't.

1. Try setting open loop to: 06
2. Try setting line length: long

Outside of that I have no clue. Pretty weird.

I bet it is a wiring problem...pairs crossed up. I would plug the SBX RJ11's directly into the Comcast Box RJ 11's bypassing all the other wiring.

Derrick may be right. If you shifted the wiring by a pin you would have the dial tone pairs split.

justbill: Yep, I agree completely!

Deltron: I tried changing loop length from short to long, but didn't try the open loop setting. I'll try that today and see. I agree it is weird.

Derrick: I was thinking that this morning, that I probably need to do a run directly from the Comcast box (which is an Arris model#TM604G/CT) to the SBX and bypass the 110 block, just in case something is wired incorrectly and I can't see it. Also, I failed to mention that the first two pairs from the Comcast box run into the 110 block and then to an alarm system, then back to the 110 block and then to the SBX. So, the first test today is to and bypass the 110 block as well as the alarm system to see if it is a simple wiring issue.

Other than those things, the only thing I could think of was a timing or signaling issue. Changing each setting one-by-one on the SBX and testing has been a bit tedious... Thanks for your all's help, I'll let you know how it goes today.

Derrick wins the prize! SBX worked fine when plugged directly into the Comcast gateway. The Comcast installer had reversed polarity between his RJ11 ends at the Comcast gateway and the 110 block. The RJ11 end was blue/white, white/blue and the 110 block was white/blue, blue/white. Apparently the alarm system didn't like that and would seize the line. I re-terminated the RJ11 ends and put the colors the opposite of the way he had them so that it was white/blue, blue/white at both the RJ11 end and at the 110 block and the phone system works fine.

Thanks for everyone's input.

I always like to hear that the fix is a hardware/wiring repair as opposed to some software glitch that no one can find a solution to (including the manu-techs) for weeks!

Sorry for my being cynical, but aside from ground start trunks, I have not encountered a polarity issue on a system's trunks in 20 years. While I'm glad that your problem is fixed, I have a hard time believing that trunk polarity was the culprit.

The polarity was the culprit because of the line being shared with the Alarm system. Some panels are very polarity sensitive. The SBX could care less.