[NTLK] Notephone and OMP/MP100 issues

[NewtonTalk]

> About the Notephones and their motherboard...
> What do you mean by "a certain degree temperature-related"?
> Do you mean that certain components are too sensitive and if
> they heat up too much they no longer work?

Having no technical documentation whatsoever, that's hard to say.

Fact is that the problem lies on the base station mainboard. If you remove
it, put it in the fridge, leave it there for an hour, take it out again,
connect it to the handset and to a phone line FAST, you'll normally get a
dial tone. "Normally" because some Notephones won't even work when the
mainboard is cold, but the majority will. If the mainboard was connected to
the keyboard, you would now be able to make a phone call. When the mainboard
warms up, the problem resurfaces. This normally takes less than a minute.
When you press and release the hook switch on the mainboard, you won't get a
new dial tone. You must put the mainboard back in the fridge for some time
first. So the problem, whatever said problem is, is DEFINITELY
temperature-related insofar that it occurs way less often when the mainboard
is cold. And it's definitely on the mainboard because apart from the handset
and the phone cable that's all you're using. And in all likeliness it is
caused because the phone lines a and b aren't getting sufficiently
high-ohmic when the hook switch is down, since this is what tells the toll
office that you've hung up.

I do not think that any components heat up too much. None of them seems
overly hot to the touch while the problem is there. Spraying components with
coolant spray doesn't help. It seems that after the problem shows up, the
whole mainboard needs a longer rest in the fridge to make it work again for
the next couple of moments. 

I cannot make any educated guess here. Normally you can find
temperature-related problems comparatively easy with a hairdryer and a can
of coolant spray. But all attempts I made so far failed miserably. On one
board I replaced all electrolytic capacitors, but this didn't fix things,
either. But I think you can safely assume that the problem lies somewhere
between the cradle switch (which, as I said, is perfectly OK) and the phone
lines a and b. After all, it's those phone lines that tell the toll office
that you've hung up, and this message obviously doesn't come. Or it doesn't
come clear enough or long enough. It might even be possible that the
Notephone isn't defective at all, but simply can't work with the voltage
nowadays supplied to the phone lines a and b. Normally this used to be
around 60 Volt, but phones were able to work OK with much less than that
because there'd be a voltage loss if your phone was located far away from
the toll office. A Fritzbox, for example, will only provide around 35 Volt
to their analog phone sockets.

If I ever find the time to tackle this again, I'll probably educate myself
first what must happen on the phone line to signalize that you've hung up,
and then start measuring backwards. It'll be difficult, though, because
there are some weird integrated circuits along this path.

Cheers

Frank

-- Newton software and hardware at http://www.pda-soft.de