66 Block flapping?

[iolair]

I have a standard 25 pair phone cable connected to a 66 block on each end. When I test the line with a 9 volt battery, I get a constant 9 volts. When I terminate one end, I get continutity. When I hook up equipment to this line, no matter if it's phone or some other signal, it seems to flap - that is, it's up for 7 seconds, down for 7 seconds. Obviously, this won't work for communication. Could a PBX be sending a "beacon" on this line that would disrupt communications?

Iolair MacWalter
Network Engineer

 

[trvlr1]

It sounds like you have routed the cable through an area where a piece of equipment is inducing this cycle. You may need to replace this cable with a screened cable to try to eliminate the issue. Prior to doing that though, have you disconnected one of the pairs from the "near end" prior to going on to the 25 pair and connected it to a phone to make sure it works before hitting the cable? Also, what kind of distances are involved here, there are different limits for digital versus analog phones. Lastly, have you tried running another cable (ie a CAT 5) along the ground temporarily to see if that works?

 

[iolair]

Thanks. I have not disconnected the near end, will try that. Distance is about 250'. I have not done a "sweep" of the run, as it's existing cable, and it is between two buildings, so laying a cable along the ground would require laying across a roadway. (private roadway, but does see light traffic). I'll check the run and see if any equipment might be interfering. Thanks for pointing me in the right direction.

Iolair MacWalter
Network Engineer

 

[SYQUEST]

What kind of protection does the cable have @ the building entrances?
Have you done a resistance check on the pairs?

A 9 volt battery is not a very reliable test. It might provide some continuity indication, but in relation to what?

....JIM....

 

[iolair]

The cable was installed by AT&T, so whatever protection they normally use would be in place. I think it's one of those gas charged cylinder devices with anti-static and anti-lightning that they use.

As far as resistance goes, the pairs were in the normal range for that distance.

Can you suggest a better test than a 9 volt battery? I have an ohm meter, but not an oscilloscope. And no, I am not an electronics engineer.

Iolair MacWalter
Network Engineer

 

[trvlr1]

If the protection cylinder is removable, you might want to try unplugging and then replugging at both ends, I have seen this take care of many issues that are otherwise unexplainable on these devices. Were you able to confirm that the input to the cable is good?

 

[ANFPS26]

Make sure you don't have a split pair. I've seen split pairs cause some strange behavior.

Jim

 

[letman2]

the cable could be getting wet between the two buildings. Using a volt ohm meter check for grounds and or shorts on the pairs.

 

[iolair]

Update - resolved. I remembered that in 1998 this cable was the victim of backhoe fade. Apparently, the repair to that cut was failing. I had buildings and grounds dig it up, and we found the "loose" connection. Not sure what was causing it to cycle regularly, but problem solved. Thanks to all who helped!

Iolair MacWalter
Network Engineer