Lastly, the ground is the + side of the 48VDC. I share this here since the
bias on the phone lines was -48VDC (below earth ground) to help prevent
corrosion of the copper wires.

Another thing I seem to recall is that the scan "off hook" current requires
approximately 20mA.

Bob

"Fred McKenzie" wrote in message
...
In article , Adam
wrote:
The responses to your question appear to contain all the information you
need to find the source of your problem, but scattered among them!

Basically, the phone presents a relatively low resistance across the phone
line when the hook-switch closes. Reacting to the resulting current, a
current-sensing relay at the central office closes, and a dial tone is
sent back down the line.

The telephone's dial is also connected across the phone line. When you
dial, a short circuit is intermittently connected across the line to
generate a number of higher-current pulses corresponding to the number
dialed. In your case, the current caused by dialing activates the
current-sensing relay, which had NOT been previously activated by the hook
switch.

Using an Ohmmeter in conjunction with the diagram, you should be able to
troubleshoot the problem. As someone mentioned, you must disconnect the
phone first, because the 48 Volts DC from the phone company might damage
your meter!

Someone mentioned a third wire that had to be connected to get a phone to
work. Modern telephones use two wires to connect to the phone company,
but early phones had a third wire used for party lines. In addition to
using different ringing frequencies to signal individual parties on the
line, the phone company also could apply the ringing voltage from one side
of the line to ground, the other side of the line to ground, as well as
line-to-line as is done today. If such a third wire were not connected,
the ringer would not work but calls could be made.

Fred