From: Frank Gruendel (fg2_at_pda-soft.de)
Date: Mon Apr 18 2005 - 15:38:04 PDT
Hi folks,
I have again spent some time on nailing down this
bloody NotePhone defect which manifests itself in
the NotePhone's being unable to hang up.
This is quite technical, but just in case someone
has such a phone and is in the mood for some
creative defect-hunting, I would like to share my
findings.
To understand WHY the phone company thinks that
the Notephone doesn't hang up, one needs to recall
the time when phones were made of copper and iron
and a bit of coal dust and not much else. Back
then (and still today) there were only two phone
lines required. Those were, at least in Germany,
named a and b.
The phone company feeds a DC voltage to the phone via
the a and b lines. I am not sure about the exact
value, but it is usually at least 20 volt. When
the receiver isn't off-hook, line a is internally
connected to whatever makes the phone ring.
This block has a high internal
resistance, hence almost no current flows and the
20 volt the phone company applies do not change=20
because the phone isn't a load worth speaking of.
If you pick the receiver up, the a line is connected
to the dialing / speaking block. This block has a
much lower internal resistance, which will cause
a voltage drop to about 12 volt. The phone company
now knows that you picked the receiver up because of
course the voltage will drop at their end of the a
and b lines, too.
This being so, I estimated that if the phone company
thinks my receiver is off-hook although it isn't,
this must be because the voltage across the a and b
lines is less than it should while the receiver
is on-hook.
With no phone connected at all, the
voltage across a and b was 20 volt. Connecting the
phone reduced this voltage to about 10 volt. So my
theory is correct. While the NotePhone shows the
defect, the voltage in the range reserved for
the receiver being off-hook.
While the Notephone warms up (with the receiver
on-hook), the voltage slowy increases.
Once it has reached 20 volt, lo and
behold, the phone company notices that the receiver
is on-hook and cuts the connection.
The question now is WHY the voltage across a and b
is too low for as long as the NotePhone shows this
defect. So far I have no idea, but it is food for
thought and further evaluation.
It is, by the way, no use to measure the internal
resistance of the NotePhone directly while the phone
lines aren't connected. In this case is indefinite
regardless of whether the receiver is on or off the
hook.
One more thing. A couple of days ago I bought a brand
new notephone. It showed the same defect.
Hence the problem we are trying to solve is
not caused by actually _using_ the phone, but
solely on the phone's age.
In a nutshell, the challenge is "Find the component
that has become temperature-dependant due to old
age". Once you tell me which component this is, a
free 2100 or eMate will be on its way to you, generously
padded with the finest chocolate available in
Germany. Good luck. Might help to get hold of one of the
old Siemens technicians...
Any ideas are more than welcome
Frank
-- Newton software and hardware at http://www.pda-soft.de
-- This is the NewtonTalk list - http://www.newtontalk.net/ for all inquiries Official Newton FAQ: http://www.chuma.org/newton/faq/ WikiWikiNewt for all kinds of articles: http://tools.unna.org/wikiwikinewt/
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