On Wed, 19 Oct 2005 00:31:37 +0100, Peter Duck
put finger to keyboard and composed:

In message
Franc Zabkar wrote:

the relay (soldered) has approx 20kohms between the coil and 200k
between the output, when dis/reconnecting the dialtone returns but then
again goes busy by itself!

That's the same behaviour you get when you take your phone offhook and
allow the dialtone to time out. It means that something is placing a
load across the line, but not a dead short. If the relay contacts are
open, then the only other culprit that comes to mind is a MOV, but IME
these usually fail OC. I'd measure the voltage between the tip and
ring inputs. In my case it is 53V when on-hook and about 10V when
off-hook. Disconnect various components until the voltage is back to
normal.

Many phones, and some modems, have a diode bridge across the line to
power part of the electronics (in a non-DECT phone, all of it).

These tend to go leaky when a surge, e.g. lightning somewhere near,
causes damage short of total destruction ...

AFAICS the diode bridge (in a transformer based modem) would always be
on the host side of the relay contacts, not the line side. The only
circuitry on the line side would be the ringer, and this would be
isolated by a 1uF 250V DC blocking cap.

-- Franc Zabkar

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