sundance-communications.com/forum Forums Wiring - Telecom Carriers - Trunks & Services Telecom Service & Providers ATT HSI Elite DSL overvoltage

We recently installed a new phone system in a small business. Four lines. One of the lines has ATT HSI Elite DSL service on it. The line worked fine on the existing Avaya, works fine on a Samsung OS7100 but will not work - no dial tone - on the new phone system. Found out the off-hook voltage is too high - 12 VDC. The new phone system will not function properly on anything over 6 VDC. When going off-hook with the new system ATT thinks we are sending a digit 1 and all you hear is silence - ATT waiting for more digits. ATT will not help. What have you done in this situation to damp-down the voltage?

What is the new system? In all fairness, off-hook voltage is dependent on loop current and if the system isn't putting a low enough resistance across the line the voltage will be high. What is the OH voltage with the Avaya system, a butt set?

I know that most DSL and cable modems as well as FiOS ONT's don't meet Bell System standards but I'm beginning to see poorly designed systems also. I don't think the new generation cares about POTS anymore, only about SIP and PRI.

-Hal

So both the system AND the service are non-spec.

First, do you have an DSL isolator/stopper between the system and the incoming service?

Second, jury rig time. Get 4 each, 3 volt - 2 to 5 watt or better zener diodes. These must all be identical parts! Connect 2 nose to nose or tail to tail, makes no difference. just NOT nose to tail or tail to nose. Do it again with the other two. Place 1 pair in the Tip lead. Place the other pair in the Ring lead. TA-DA, you now have a 6 volt drop in your service. 12 minus 6 = 6 volts. Typical off-hook voltage.

Why 4 3-volt zener diodes. When you hook them Nose to Nose or tail to tail the total voltage drop is 3.6 volts. AND it doesn't block AC ringing! It will however knock ring voltage down 6 volts. If that creates another problem, you're on your own. (To quote "Jim" on Taxi, you can only go to the well just so many times)

The new phone system is a Vertical SBX IP 320. It has been used in Asia for a while and has been repackaged for the USA recently. I have not checked the OH voltage on the Samsung and Avaya. I can take a Samsung back and do so. I tend to agree that many mfg. are running toward SIP in the SMB market. SIP is very expensive here in Saginaw, Mi and not all SIP providers are certified with phone mfgs. Lightninghorse has a way to drop the voltage with zener diodes. I will give this a try. Thanks for your input.

The new phone system is a Vertical SBX IP 320. It has been used in Asia for a while and has been repackaged for the USA recently.

I would say that that could be the problem. Manufacturers make one system that they can sell all over the world and make lots of money. Different systems for different countries cost money. Unfortunately telephone services differ from country to country and I don't think it's an easy thing to make one system work with all the different POTS specs. SIP on the other hand is easier to design for.

-Hal

Thanks Lightninghorse. I used the zener diodes to drop the voltage but I still had the problem of no dial tone. We found that the SBX was simulating the digit 1 and therefore quieted dial tone when you accessed the line. The C.O. was waiting for the other 10 digits. So I jury rigged an electrolytic cap in series with a resistor across the line. This presumably works to absorb the C.O. relay bounce in the SBX that generates the digit 1.

Out comes the revolver, 'now I've seen/heard it all'..... no wait, I remember that problem when I was next door, literally, to a SLIC hut and with an Asizu(?) phone system 15-18 years ago! In that case, the customer was pretty much looking for any excuse to get a new system, and we were happy to accomodate him. We even put the old system in OUR dumpster!