>> 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
>> term>> 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?
> The capacitor is probably part of an RF shield on the jack.[snip]
The capacitor is used to "terminate" the line with a value that approximates one standard ringer, so that if someone calls in a trouble report, the tester can check if (s)he "sees" the capacitor with the NI jack disconnected. Depending on local practice, the Central Office might be programmed to report a fault on any line that it rings which doesn't show a ringer attached, so you should leave it alone.
It doesn't hurt anything.
William
(Filter noise from my address for direct replies)