TELECOM Digest OnLine - Sorted: Re: Question About "Network Interface" Phone Jack

Re: Question About "Network Interface" Phone Jack

Tony P. (
Tue, 26 Jul 2005 19:32:02 -0400

In article <>, says:

> After living in the same place in New York City for years, I recently
> moved to another place (also in New York City). The room I moved to
> has an existing phone jack but it looks different from the old
> square-ish ones I'm accustomed to. (The old ones consisted only of 4
> terminals inside the case). This new one is rather rectangular and
> has a label on the outside that says:

> Network Interface
> *Caution
> Disconnect plug from this jack during installation and repair
> of wiring.
> *Testing
> Plug working phone directly into this jack. If phone operates,
> fault is in wiring. If phone does not operate, call repair
> service.

> When I opened the case, I noticed that the red and green wires (the
> only ones that will be actually used by the telephone itself) are also
> connected to a little circuit board whose most conspicuous component
> is a yellow cylinder-shaped object (about 3/4" long and about 3/8"
> diameter) with the following markings ...

> 250V
> TI
> 0.47 MFD
> +/- 10%

> * What is the purpose of this circuit board?
> * Is it really necessary? (How come the old-fashioned jacks
> didn't have this?)
> * What if I were to disconnect it?

> Also, when I looked inside the jack itself (the hole where you would
> plug the phone into), I noticed there's some strange-looking gunk
> inside. It's clear-colored and has the consistency of rubber cement.

> * Is this something that's supposed to be there?
> * What is it used for?

The capacitor is probably part of an RF shield on the jack. The goo as
an anti-corrosive gel. Copper and brass and all sorts of metals
corrode over time. This prevents the jack from getting gunked up.

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