rickman wrote:
> On Jul 23, 3:17 am, Neil <NeilKu...@worldnet.att.net> wrote:
>> rickman 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
>> If it is a lot of board, and they are not too expensive, Try more
>> current.  1 amp is a lot.  Something should be getting warm.  If it is
>> not the board, that leaves wrong / bad components, backwards parts, and
>> a schematic error.
> 
> 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.  Handing the board wearing gloves
> would leave a larger thermal imprint than this.
> 
> But using a FLIR camera does sound like fun!
> 

It might make sense to rent one, find the short, then take it home and 
image your house from the outside. It'll find all the leaky areas where 
heat or A/C losses occur. One guy found a really hard signal near a 
crawl space vent. Turned out an A/C duct had fallen off.

-- 
Regards, Joerg

http://www.analogconsultants.com/

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

Il 23/07/2008 17.53, rickman ha scritto:
[snip]
> 
> Good idea!  When I get some time I will try this.  Thanks.
> 

Buy a bag of very "light" iron powder (I saw that on sale on USA); take 
a thin glass panel out from a window, cover it with water and a drop of 
soap, mix the iron powder in the water, and carefully put the whole 
panel upon your board. Put many amps across the board.
Watch the magnetic flux lines around the current path.
Clean up the whole mess...

:-)

(I just looked a video of a guy building magnetic field "readers" with 
bottles, water, and iron poweder... fun pictures!)

Seriously, when I was interested in knowing where the short happened, I 
used some dedicated instruments; it was very quick and effective. I'm 
not at work now and I don't recall the model.

Basically, a gradient search should tell you where the short is located.

But if you just need the board, I would simply blow it up ad many said.

On Jul 23, 11:51 am, CBFalconer <cbfalco...@yahoo.com> wrote:
> Paul Keinanen wrote:
> > Didi <d...@tgi-sci.com> wrote:
>
> >> Yes, that's a clear advantage of the 110V  (one can expect twice
> >> the current at 220 is needed to blow the fuses), but 220 is still
> >> more fun for this application - sparkles, smoke, danger etc.
>
> > By the way, can you make a hot sausage in a 110 V country by just
> > sticking the neutral at one end of the sausage and live conductor
> > into the other end ?
>
> No, that operation here requires an adaptor and half-length
> sausages.  :-)

I have a hot dog cooker around here somewhere from when I was a kid.
It has two rows of spikes that you impale the dogs between.  When you
close the lid, it complete the circuit to the 110 VAC and the dogs
cook in 2 or 3 minutes.  Pretty cool huh?  But they get a slightly
metallic taste so I guess that's why you don't seem them in the stores
now.

Rick

In article <c4e5b06b-e453-468e-8c00-95750fce94d7
@x41g2000hsb.googlegroups.com>, g...@gmail.com says...
> On Jul 23, 11:51 am, CBFalconer <cbfalco...@yahoo.com> wrote:
> > Paul Keinanen wrote:
> > > Didi <d...@tgi-sci.com> wrote:
> >
> > >> Yes, that's a clear advantage of the 110V  (one can expect twice
> > >> the current at 220 is needed to blow the fuses), but 220 is still
> > >> more fun for this application - sparkles, smoke, danger etc.
> >
> > > By the way, can you make a hot sausage in a 110 V country by just
> > > sticking the neutral at one end of the sausage and live conductor
> > > into the other end ?
> >
> > No, that operation here requires an adaptor and half-length
> > sausages.  :-)
> 
> I have a hot dog cooker around here somewhere from when I was a kid.
> It has two rows of spikes that you impale the dogs between.  When you
> close the lid, it complete the circuit to the 110 VAC and the dogs
> cook in 2 or 3 minutes.  Pretty cool huh?  But they get a slightly
> metallic taste so I guess that's why you don't seem them in the stores
> now.
> 

I suspect that, even with a lid interlock switch, it wouldn't meet
current UL standards.  If a dog falls off the neutral end, you
might get a ground fault or a hot chassis.

Given the ubiquity of the microwave oven, it's probably easier
to put a few vent holes and nuke it for 30 seconds.


Mark Borgerson

*Fun thread*

You guys need a 100µF 500V Electrolytic cap for that! They are cheap 
because they're standard filter-caps in guitar amplifiers.

I know for sure that they can melt copper-trace with ease. They also 
have enough power to fry your DMM and weld the probes onto the circuit 
board as well :-)

Been there, done that..

Nils <--- who builts tube guitar amplifiers every once in a while, just 
because it is so much fun the see arcs and sparcs on a cicuit-board.

On Jul 23, 12:45 pm, Antonio Pasini
<removethis_antonio.pas...@alice.it> wrote:
> Il 23/07/2008 17.53, rickman ha scritto:
> [snip]
>
>
>
> > Good idea!  When I get some time I will try this.  Thanks.
>
> Buy a bag of very "light" iron powder (I saw that on sale on USA); take
> a thin glass panel out from a window, cover it with water and a drop of
> soap, mix the iron powder in the water, and carefully put the whole
> panel upon your board. Put many amps across the board.
> Watch the magnetic flux lines around the current path.
> Clean up the whole mess...
>
> :-)
>
> (I just looked a video of a guy building magnetic field "readers" with
> bottles, water, and iron poweder... fun pictures!)

I seem to recall a magnetic liquid with some very unusual properties.
I don't recall the exact form, but in all of the images I saw it was
intact and 3D.  It would illustrate some very odd fields, one caused
it to look like a spiky soccer ball.  Anyone know what it was?

Rick

On Jul 23, 12:40 pm, Joerg <notthisjoerg...@removethispacbell.net>
wrote:
> rickman wrote:
> > On Jul 23, 3:17 am, Neil <NeilKu...@worldnet.att.net> wrote:
> >> rickman 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
> >> If it is a lot of board, and they are not too expensive, Try more
> >> current.  1 amp is a lot.  Something should be getting warm.  If it is
> >> not the board, that leaves wrong / bad components, backwards parts, and
> >> a schematic error.
>
> > 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.  Handing the board wearing gloves
> > would leave a larger thermal imprint than this.
>
> > But using a FLIR camera does sound like fun!
>
> It might make sense to rent one, find the short, then take it home and
> image your house from the outside. It'll find all the leaky areas where
> heat or A/C losses occur. One guy found a really hard signal near a
> crawl space vent. Turned out an A/C duct had fallen off.
>
> --
> Regards, Joerg

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.

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...  :^)

On the other hand, I am getting very worried about making enough money
to be able to fill my heating oil tank this year.  After all, I only
make an engineer's pay.  It might not be long before I sell the
furnace as scrap to pay for electric space heaters!!!

Rick

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. :)

-- 
emboliaschizoide.splinder.com

rickman 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

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.
Non-destructive methods are usually preferred.

-- 
********************************************************************
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..
********************************************************************

On Jul 23, 8:53 am, rickman <gnu...@gmail.com> wrote:
> On Jul 23, 10:27 am, "dkel...@hotmail.com" <dkel...@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
>
> Good idea!  When I get some time I will try this.  Thanks.
>
> Rick


Hi
 The main trick is to get enough drop along the trace. Use as much
current as
you can. For smaller traces, I've used 1 to 5 amps someplace.
 This trick even works for power plane to power plane shorts but you
need
to do two different directions across the plane that you are driving
power
across. You form two lines of zero volts. Where they cross is the
location of
the short.
 If the 12v line has branches, you may find the zero volt is down a
branch. Just
move the location of one of the current injection points to the end of
the branch
and search along the branch for the zero volt location.
Dwight