sundance-communications.com/forum Forums Other TDM Phone Systems Other Telephones & Systems ISDN rack mounted power supply issue

We have a government customer that has about thirty 48-port racks for ISDN NT-1 units. Most of them are fairly old. What we are finding with them is that if they lose power, they won't come back up on their own and the alarm light on the power supply just flickers.

The only way that we've found is to unplug all of the phones from the racks, one at a time. Usually, when we get about 3/4 of them unplugged, you hear a relay click within the power supply and they rack comes back up. We then have to plug all of the station cables back in.

This is not a problem with some of the newer racks at the site. I'm wondering if anyone knows of a fix for this or a better work around. It is very time consuming when we have a closet with six racks lose power.

Ed,

Sounds like the power supplies are just plain worn out and just can't bring all of the NT1 cards back up at once. Is it possible/cost effective to plug the racks into a UPS? If that is not a solution, we have had to rewire a few "tombstone" racks with new rectifiers. It was as simple as pulling the old power supply, cutting the power cables and splicing in the new leads from the rectifier. You could get a rack mount -48/+24vdc rectifier and power the racks in each room, with one rectifier.

I think that it is more of a design issue. We have some newer racks that don't have this problem. Most of the ones we're having this problem with were made by Lucent. They are all on APC UPS units, but people get sloppy when in the closets and bump the power cords, etc.

It's not the populated NT1 cards that create the load issue; it is the sets themselves. I suppose that we could advise the customer to unplug every affected set at the desktop, but being a government agency, nobody is willing to do anything that doesn't fall into their job description. The customer doesn't want to spend any money for a major upgrade (power supply replacements, etc.), and they don't mind paying us to come out and reset them. It is more about the response time, since it takes us at least an hour to get there when an outage occurs.

I was just hoping that there might be an option within the power supply to override what appears to be an overload protection mechanism.

Sounds like those power supplies are experiencing high saturation losses during power up meaning you have components failing. A good electronics shop good could fix it but since you can't take any offline there's no way to even try.