Question About "Network Interface" Phone Jack

Jul 24, 2005 0 Replies

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?


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