Paul Keinanen wrote:
> ....
> >> I don't think I'll rent the FLIR camera, but I sleep well at night
> >> knowing I don't have to worry about Radon building up inside...  :^)
> >>
> >
> >Why is everyone concerned about Radon? Does it really occur a lot?
>
> Radon can be a problem in houses built on sand that has been recently
> (e.g. during the Ice Age) split from some uranium rich stones, such as
> granite.
>
> Instead of ventilating the whole house, just make 2-3 vertical holes
> under the house and install an air pumps sucking the air and radon out
> of these wells and blow it outside the house. The slight
> under-pressure in the wells will such the air from the surrounding
> sand and thus prevents the radon from entering the house through the
> floor.

LOL, try entering such a discussion on the radsafe mailing list.
Or just look at the archives over the last say 10 years and be
overwhelmed... :-).
There are two camps: one says radon can cause lung cancer,
the other says it prevents it actually... (hormesis being assumed
to be the cause for that).
These are the extremes, of course, and even those propagating them
like the rest state that it is really hard to gauge the effect of
radon
on lung cancer incidents as smoking outweighs it by far and defacto
masks the result of any study done (two major ones I know of). Or if
it does not mask them it makes them a lot less convincing (I am
not that deep into that).

Didi

------------------------------------------------------
Dimiter Popoff               Transgalactic Instruments

http://www.tgi-sci.com
------------------------------------------------------
http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/

Original message: http://groups.google.com/group/comp.arch.embedded/msg/d64babe473048109?dmode=source

rickman wrote:
> On Jul 23, 6:17 pm, Joerg <notthisjoerg...@removethispacbell.net>
> wrote:
>> dalai lamah wrote:
>>> Un bel giorno rickman digitò:
>>>> Many posts indicate that I should expect the something to be getting
>>>> warm from the 1 Amp of current.  Yes, the power supply is getting
>>>> warm.  The voltage on the board is only 5 mV max.  That equates to 5
>>>> mW.  I think it would take a very sensitive device to see the
>>>> temperature rise from 5 mW of power.
>>> Tsk, amateurs. Use a 12V battery car instead, and let monsieur ampere do
>>> his job. :)
>> A car battery? And then you end up with one hellacious hole where the
>> short was, having turned a non-working PCB into a definitely dead PCB.
>>
>> --
>> Regards, Joerg
>>
>> http://www.analogconsultants.com/
>>
>> "gmail" domain blocked because of excessive spam.
>> Use another domain or send PM.
> 
> Why does everyone think that the short will be the part that blows?
> It could just as well be any point in the current path.  Even if there
> are power planes (there are) the current has to get into the plane and
> that is the point that could blow instead of the short.
> 
> Rick
I did ask how many you had.  No the short may not go first.  It is just 
something to try. I once had 60 boards with defective(shorted) 
decoupling caps. I burned them out, no board damage.
PCB shorts can be tiny (Yours is not) or the FR4 smokes.  If a trace 
burnsit may tell you where to look on the other boards.

d...@hotmail.com wrote:
> On Jul 22, 9:30 am, rickman <gnu...@gmail.com> wrote:
>> I have a small module that is shorted between the +12 volt plane and
>> ground.  I am having a hard time finding where the short is so it can
>> be fixed.
>>
>> The bare boards were supposed to be tested, so I don't suspect the
>> board itself.  I have visually inspected everything I can including
>> looking under the chips as much as I can see and found no sign of a
>> problem.
>>
>> My bench supply current limits (foldback actually) and I am seeing
>> about an Amp into the 12 volt rail.  Probing with a volt meter I can
>> see 10 mV at the point where I connect the power to the board.  This
>> drops to about 1 mV on the other edge of the board.  But I can't find
>> a particular point where the voltage says "here it is"!
>>
>> Any ideas on how to find and fix this short?
>>
>> Rick
> 
> Hi Rick
>  I've described this methode before. Most people seem to think
> that a method of finding the short requires feeding current through
> the short. My method uses a different idea.
>   Put your supply across the 12v line, from one end to the other,
> in current limit. The line then has a small voltage drop across it.
>  Place a DVM lead on the ground. The location isn't important
> since there is no current in the ground.
>  Use the 200mv scale. This works best with a 4 or 5 digit meter.
> With the other lead, probe along the 12V line. When the meter
> reads closest to zero, you are at the location of the short.
>  I have used this method many times when other methods
> seem to fail.
>  The idea is to consider the 12 v line to be like a resistor with
> a tap on it. The ground it the tap. With the second lead as
> another tap, when both taps are at the same location along
> the resistor, there is 0 volts.
> Dwight
Nice!  I will give it a shot next time.

On Jul 24, 12:12 am, Paul Keinanen <keina...@sci.fi> wrote:
> On Wed, 23 Jul 2008 14:44:20 -0700, Joerg
>
> <notthisjoerg...@removethispacbell.net> wrote:
> >rickman wrote:
> >> Let's see... the board cost $150 to make and a FLIR camera cost maybe
> >> $500 to rent.  My ducts are in the basement where I can see them all
> >> and this 50 year old house is nothing but a draft with windows.
>
> >That's going to cost you in winter.
>
> >> I don't think I'll rent the FLIR camera, but I sleep well at night
> >> knowing I don't have to worry about Radon building up inside...  :^)
>
> >Why is everyone concerned about Radon? Does it really occur a lot?
>
> Radon can be a problem in houses built on sand that has been recently
> (e.g. during the Ice Age) split from some uranium rich stones, such as
> granite.
>
> Instead of ventilating the whole house, just make 2-3 vertical holes
> under the house and install an air pumps sucking the air and radon out
> of these wells and blow it outside the house. The slight
> under-pressure in the wells will such the air from the surrounding
> sand and thus prevents the radon from entering the house through the
> floor.
>
> Paul

I have never heard that radon problems required the presence of sandy
soils.  The area I am in has few sandy soils and is part of a wide
area that can have radon problems.  It *is* very individual.  Two
houses next to each other, one can have a significant level while the
other has very little.  A lot has to do with the mirco-geography
(specifics of the soil and strata under the house) and the
construction.

BTW, anyone who doubts that radon can cause health problems is not
being very bright.  Radon is radioactive and is clearly a health
threat.  I suppose someone could challenge the levels at which the
health risk becomes significant, but then that always happens doesn't
it?  I bet those are the same people who believe in homeopathy and
poltergeist.  Oh, I shouldn't have said that.  Now the thread will
turn to the metaphysical and it will be my fault!

Rick

On Thu, 24 Jul 2008 02:29:29 -0400, Neil <N...@worldnet.att.net>
wrote:

>d...@hotmail.com wrote:
>> On Jul 22, 9:30 am, rickman <gnu...@gmail.com> wrote:
>>> I have a small module that is shorted between the +12 volt plane and
>>> ground.  I am having a hard time finding where the short is so it can
>>> be fixed.
>>>
>>> The bare boards were supposed to be tested, so I don't suspect the
>>> board itself.  I have visually inspected everything I can including
>>> looking under the chips as much as I can see and found no sign of a
>>> problem.
>>>
>>> My bench supply current limits (foldback actually) and I am seeing
>>> about an Amp into the 12 volt rail.  Probing with a volt meter I can
>>> see 10 mV at the point where I connect the power to the board.  This
>>> drops to about 1 mV on the other edge of the board.  But I can't find
>>> a particular point where the voltage says "here it is"!
>>>
>>> Any ideas on how to find and fix this short?
>>>
>>> Rick
>> 
>> Hi Rick
>>  I've described this methode before. Most people seem to think
>> that a method of finding the short requires feeding current through
>> the short. My method uses a different idea.
>>   Put your supply across the 12v line, from one end to the other,
>> in current limit. The line then has a small voltage drop across it.
>>  Place a DVM lead on the ground. The location isn't important
>> since there is no current in the ground.
>>  Use the 200mv scale. This works best with a 4 or 5 digit meter.
>> With the other lead, probe along the 12V line. When the meter
>> reads closest to zero, you are at the location of the short.
>>  I have used this method many times when other methods
>> seem to fail.
>>  The idea is to consider the 12 v line to be like a resistor with
>> a tap on it. The ground it the tap. With the second lead as
>> another tap, when both taps are at the same location along
>> the resistor, there is 0 volts.
>> Dwight
>Nice!  I will give it a shot next time.

In general, IMHO, it's best to use a beefy current source limited to
250mV or so. Then you can put it pretty much on any two points on a
board without blowing things up (well, except very low resistance
fuses, very low value resistors, perhaps some very low resistance
coils). You won't even be outside the specs on most chips, where
+/-300mV is typically allowed. 
Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
s...@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

"Paul Keinanen" <k...@sci.fi> wrote in message 
news:4...@4ax.com...
> On Wed, 23 Jul 2008 19:49:58 +0100, "Paul E. Bennett"
> <P...@topmail.co.uk> wrote:
>
>>In reviewing some of the other replies I noticed that no one had yet (at
>>the top level of the tree) suggested using a signal injector and a trace
>>probe. By injecting a current driven signal onto the power rail and
>>ground you can prod around with the trace probe and determine where the
>>short is by the signal level dropping nearest the location.
>
> What kind of signal would that be ?
>
> Using a variable frequency RF-generator you should be able to
> determine when the tracks and the short is resonated e.g. at 1/2 or
> 1/4 wavelength. After determining the PCB material and hence the
> velocity factor, you should be able to determine the distance from the
> feedpoint.
>
> One other method would be to inject a sub-nanosecond pulse edge and
> determine, how long it takes for the reflection from the short to
> return back to the generator.
>
> A different approach would be to inject a significant current into the
> +12 V line and try to detect the magnetic field on the +12 V trace,
> until it disappears into the ground plane. This should work even if
> the +12 V trace is within a multilayer PCB. Some Hall sensor might
> useful, if DC current is used to create the magnetic field, but if an
> AC (mains /audio frequency) current is running in the trace, some
> pick-up coil should be able to pick up the stray magnetic field.
>
> Paul
>
In the distant past I have used a milli-ohm meter for this, but alas, those 
don't seem to be in everyone's test cabinet.  Also, that didn't always find 
a big short.

Other than blowing the crap out of everything on the board with AC, a 12V 
supply that won't current limit might work.

Grant Edwards wrote:
> On 2008-07-23, Joerg <n...@removethispacbell.net> wrote:
> 
>>> Tsk, amateurs. Use a 12V battery car instead, and let monsieur ampere do
>>> his job. :)
>> A car battery? And then you end up with one hellacious hole
>> where the short was, having turned a non-working PCB into a
>> definitely dead PCB.
> 
> The subject is finding the short, not fixing the short. ;)
> 

Yep, and after the smoke has wafted off and the fire engines have left 
the scene one can with certainty say "There must have been a short" :-)

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

rickman wrote:
> On Jul 23, 6:17 pm, Joerg <notthisjoerg...@removethispacbell.net>
> wrote:
>> dalai lamah wrote:
>>> Un bel giorno rickman digitò:
>>>> Many posts indicate that I should expect the something to be getting
>>>> warm from the 1 Amp of current.  Yes, the power supply is getting
>>>> warm.  The voltage on the board is only 5 mV max.  That equates to 5
>>>> mW.  I think it would take a very sensitive device to see the
>>>> temperature rise from 5 mW of power.
>>> Tsk, amateurs. Use a 12V battery car instead, and let monsieur ampere do
>>> his job. :)
>> A car battery? And then you end up with one hellacious hole where the
>> short was, having turned a non-working PCB into a definitely dead PCB.
>>
>> --
>> Regards, Joerg
>>
>> http://www.analogconsultants.com/
>>
>> "gmail" domain blocked because of excessive spam.
>> Use another domain or send PM.
> 
> Why does everyone think that the short will be the part that blows?
> It could just as well be any point in the current path.  Even if there
> are power planes (there are) the current has to get into the plane and
> that is the point that could blow instead of the short.
> 

That's why the blunt application of a car battery isn't the ticket. You 
have to pipe in the current via connections which may or may not have 
thermal reliefs. The more the better. Power planes must feature such 
connection areas. Then gauge what this connection can safely take and 
crank things up. If the short doesn't blow before reaching the pain 
threshold it probably ain't going to work.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Jul 24, 12:53 pm, Joerg <notthisjoerg...@removethispacbell.net>
wrote:
> rickman wrote:
> > On Jul 23, 6:17 pm, Joerg <notthisjoerg...@removethispacbell.net>
> > wrote:
> >> dalai lamah wrote:
> >>> Un bel giorno rickman digit=F2:
> >>>> Many posts indicate that I should expect the something to be getting
> >>>> warm from the 1 Amp of current.  Yes, the power supply is getting
> >>>> warm.  The voltage on the board is only 5 mV max.  That equates to 5
> >>>> mW.  I think it would take a very sensitive device to see the
> >>>> temperature rise from 5 mW of power.
> >>> Tsk, amateurs. Use a 12V battery car instead, and let monsieur ampere=
 do
> >>> his job. :)
> >> A car battery? And then you end up with one hellacious hole where the
> >> short was, having turned a non-working PCB into a definitely dead PCB.
>
> >> --
> >> Regards, Joerg
>
> >>http://www.analogconsultants.com/
>
> >> "gmail" domain blocked because of excessive spam.
> >> Use another domain or send PM.
>
> > Why does everyone think that the short will be the part that blows?
> > It could just as well be any point in the current path.  Even if there
> > are power planes (there are) the current has to get into the plane and
> > that is the point that could blow instead of the short.
>
> That's why the blunt application of a car battery isn't the ticket. You
> have to pipe in the current via connections which may or may not have
> thermal reliefs. The more the better. Power planes must feature such
> connection areas. Then gauge what this connection can safely take and
> crank things up. If the short doesn't blow before reaching the pain
> threshold it probably ain't going to work.
>
> --
> Regards, Joerg
>
> http://www.analogconsultants.com/
>
> "gmail" domain blocked because of excessive spam.
> Use another domain or send PM.


Hi
 I believe the car battery was to be used with a lamp in series. This
is
less than 5 amps.
 Still, I recommend the method I suggested. It is non-destructive and
doesn't
require feeding high current through the short.
 I've used it for years and it has always worked. I even used it once
to find
a short on the other side of a 10K resistor than the power line. This
was
on a board with 100's of 10K resistors wired similarly.
 Since it doesn't require feeding current through the short, the
resistance
of the short relative to the trace is not important as is the method
of looking
for the drop on the trace when feeding current through the short.
Dwight

Paul Keinanen wrote:

> On Wed, 23 Jul 2008 19:49:58 +0100, "Paul E. Bennett"
> <P...@topmail.co.uk> wrote:
> 
>>In reviewing some of the other replies I noticed that no one had yet
>>(at the top level of the tree) suggested using a signal injector and a
>>trace probe. By injecting a current driven signal onto the power rail
>>and ground you can prod around with the trace probe and determine where
>>the short is by the signal level dropping nearest the location.
> 
> What kind of signal would that be ?

The current injection probe I used would put in a square wave at about
1MHz or 10kHz (switch selectable). The trace probe could find this
signal on a shorted line and give an indication of how big it was. When
you got very close to the short you would actually lose the signal.
Works best if the return is on a ground plane but can cope with other
layout practices as well. The probes usually come as pairs.
 
> Using a variable frequency RF-generator you should be able to
> determine when the tracks and the short is resonated e.g. at 1/2 or
> 1/4 wavelength. After determining the PCB material and hence the
> velocity factor, you should be able to determine the distance from the
> feedpoint.

Another good non-destructive technique.
 
> One other method would be to inject a sub-nanosecond pulse edge and
> determine, how long it takes for the reflection from the short to
> return back to the generator.

This is also good and has been used to locate the shorts in underground
cables.

[%X]

At least I have got some discussion on the non-destructive methods going.
I know it seems like no fun but there are times when a non-destructive
approach is needed. After all, having to rebuild a board that is charred
is not easy and charcoal is a bugger to solder to. ;>

-- 
********************************************************************
Paul E. Bennett...............<email://P...@topmail.co.uk>
Forth based HIDECS Consultancy
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-811095
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
********************************************************************