From: Edward Johnson (radar9999_at_aol.com)
Date: Wed Apr 20 2005 - 12:42:27 PDT
It does sound as if there is a systemic problem with manufacture. I am
not an expert and have not done component level repairs in looonng
time, but if my memory serves correctly most semiconductors (especially
transistors or varistors) are somewhat temperature dependent and want
to operate with specified temperature limitations.
Back in my troubleshooting days we used to have a piece of test
equipment called a Huntron Tracker (http://www.huntron.com/index.htm).
Some you may remember that it allows you the ability to test discrete
components that are still soldered to a circuit bd. This piece of gear
tested discrete components by applying a very low current rf signal
between two probes and displaying the resulting waveform on a small crt
on the front of the unit. The waveform shape of a known good component
can be compared with that of a suspect one. The manual that came with
it contained examples of what good & defective OR borderline defective
components look like after being tested.
snip>>>
Repair Undocumented Boards
Repair of old or unknown circuit assemblies is a challenge when
documentation is not available. Much of the test equipment on the
market is ineffective in this situation as they require information
that assumes a documentation package is available for the circuit card
to be tested.
Using equipment to test a board assembly that verifies component
signatures are good and identify those that are suspect or failing
allows for quick diagnoses and repair of the circuit. This is often
done in a non-power up mode which also reduces the risk to the
remaining components on the board in the event that either a failed
component or trace will result in undue stress to the other components
if power were applied.
<<<<<<<<SNIP
Access to technical documents describing the way the circuits are
supposed to work, along with schematics to work from, would be very
nice. But if those are not available using a huntron tracker can work.
BUT they do not appear to cheap.
(http://search.ebay.com/huntron-
tracker_W0QQbsZSearchQQcatrefZC6QQfnuZ1QQfromZR10QQfsopZ1QQftsZ1QQsacatZ
Q2d1QQsbrftogZ1QQsofocusZbs
My suggestion would be to try and contact anyone that might have
worked with the company on these units, or is still with the company on
a different product or division.
On another list I used to belong to regarding SuperMac products we
lucked into several engineers and technicians that used to work for the
company and added insight to existing documentation, as well as
engineering drawings and schematics not available to the average
schmoe! Helped out a lot to keep my unit runnning strong and compatible
with OS-X.
Hope this helps.
Ed Johnson
A Smart man learns from his mistakes. A Wise man learns from other
peoples mistakes. Be Wise!
On Apr 19, 2005, at 12:11 AM, newtontalk_at_newtontalk.net wrote:
> From: "Frank Gruendel" <fg2_at_pda-soft.de>
> Subject: [NTLK] NotePhone followup
> Date: Tue, 19 Apr 2005 00:38:04 +0200
>
> 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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