Troubleshooting 'shorted' power rails

I had two cases in a row recently of many-layer power-planed
boards with power supplies that wouldn't come up above a diode
drop, and I was able to use a trick devised for the first one to
solve the problem on the second one, too --

I set a current-limited supply to ~30mA & left the board
to stabilize thermally. I then looked for the 'hot' parts
with an IR thermometer. Worked like a charm.

Temp. rise was about 1oC @ 20mW. The IR thermometer? $14
well-spent.


Cheers,
James Arthur

 

[Lasse Langwadt Christense]

søndag den 19. maj 2019 kl. 23.23.02 UTC+2 skrev dagmarg...@yahoo.com:

I had two cases in a row recently of many-layer power-planed
boards with power supplies that wouldn't come up above a diode
drop, and I was able to use a trick devised for the first one to
solve the problem on the second one, too --

I set a current-limited supply to ~30mA & left the board
to stabilize thermally. I then looked for the 'hot' parts
with an IR thermometer. Worked like a charm.

Temp. rise was about 1oC @ 20mW. The IR thermometer? $14
well-spent.

https://youtu.be/t5fICjcaJ3E?t=15m51s

 

[bitrex]

On 5/19/19 5:22 PM, dagmargoodboat@yahoo.com wrote:

I had two cases in a row recently of many-layer power-planed
boards with power supplies that wouldn't come up above a diode
drop, and I was able to use a trick devised for the first one to
solve the problem on the second one, too --

I set a current-limited supply to ~30mA & left the board
to stabilize thermally. I then looked for the 'hot' parts
with an IR thermometer. Worked like a charm.

Temp. rise was about 1oC @ 20mW. The IR thermometer? $14
well-spent.


Cheers,
James Arthur

You can get a full thermal camera attachment for Android from the state
store for $200, sometimes less like $15-20 off on sale from time to time:

<https://www.amazon.com/dp/B00NYWAHHM/ref=twister_B07QVJVVGD?_encoding=UTF8&psc=1>

 

[John Larkin]

On Sun, 19 May 2019 14:22:57 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

I had two cases in a row recently of many-layer power-planed
boards with power supplies that wouldn't come up above a diode
drop, and I was able to use a trick devised for the first one to
solve the problem on the second one, too --

I set a current-limited supply to ~30mA & left the board
to stabilize thermally. I then looked for the 'hot' parts
with an IR thermometer. Worked like a charm.

Temp. rise was about 1oC @ 20mW. The IR thermometer? $14
well-spent.


Cheers,
James Arthur

Thermal imagers are getting affordable and are great to have around.
Not only can they find shorts and bad parts, it's good to image a new
design and see if anything runs hot.

https://www.dropbox.com/s/mlaf2yce2z3xiv7/IR_0025.jpg?dl=0

https://www.dropbox.com/s/r4q2z8vnonwh4mc/IR_Board.jpg?dl=0

Our test people use a thermal imager too, to spot unusual stuff.

One eternal problem is electronics is "where is the current going?"

Sometimes you can measure microvolt drops in traces and planes to
answer that question. It would be great if we could see mag fields!



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Sunday, May 19, 2019 at 5:23:02 PM UTC-4, dagmarg...@yahoo.com wrote:

I had two cases in a row recently of many-layer power-planed
boards with power supplies that wouldn't come up above a diode
drop, and I was able to use a trick devised for the first one to
solve the problem on the second one, too --

I set a current-limited supply to ~30mA & left the board
to stabilize thermally. I then looked for the 'hot' parts
with an IR thermometer. Worked like a charm.

Temp. rise was about 1oC @ 20mW. The IR thermometer? $14
well-spent.

What was it?

Cheers,
James Arthur

 

[Tom Del Rosso]

John Larkin wrote:

Thermal imagers are getting affordable and are great to have around.
Not only can they find shorts and bad parts, it's good to image a new
design and see if anything runs hot.

But the cheap ones have low res. What do you think is minimum useful
res?

 

[John Larkin]

On Sun, 19 May 2019 20:04:58 -0400, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote:

John Larkin wrote:

Thermal imagers are getting affordable and are great to have around.
Not only can they find shorts and bad parts, it's good to image a new
design and see if anything runs hot.

But the cheap ones have low res. What do you think is minimum useful
res?

Don't know, but what is important is that it can focus really close to
the parts. Some imagers are fixed-focussed at infinity, useless for
electronics.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Mike]

On 5/19/2019 5:04 PM, Tom Del Rosso wrote:

John Larkin wrote:

Thermal imagers are getting affordable and are great to have around.
Not only can they find shorts and bad parts, it's good to image a new
design and see if anything runs hot.

But the cheap ones have low res. What do you think is minimum useful
res?



Seek Thermal is quite adequate for the task.

In many cases, the thermal profile is low resolution.
A heat source anywhere near anything else will warm that
and 'fuzz out' any possibility of extremely high resolution.

If you get one, make SURE you get one with variable focus.
The very early ones were fixed focus and can't get close
enough. The newer ones have the SAME PART NUMBER
and variable focus. Make sure the lens rotates.

 

On Sunday, 19 May 2019 22:48:13 UTC+1, John Larkin wrote:

On Sun, 19 May 2019 14:22:57 -0700 (PDT), dagmargoodboat@yahoo.com

wrote:

I had two cases in a row recently of many-layer power-planed
boards with power supplies that wouldn't come up above a diode
drop, and I was able to use a trick devised for the first one to
solve the problem on the second one, too --

I set a current-limited supply to ~30mA & left the board
to stabilize thermally. I then looked for the 'hot' parts
with an IR thermometer. Worked like a charm.

Temp. rise was about 1oC @ 20mW. The IR thermometer? $14
well-spent.


Cheers,
James Arthur

Thermal imagers are getting affordable and are great to have around.
Not only can they find shorts and bad parts, it's good to image a new
design and see if anything runs hot.

https://www.dropbox.com/s/mlaf2yce2z3xiv7/IR_0025.jpg?dl=0

https://www.dropbox.com/s/r4q2z8vnonwh4mc/IR_Board.jpg?dl=0

Our test people use a thermal imager too, to spot unusual stuff.

One eternal problem is electronics is "where is the current going?"

Sometimes you can measure microvolt drops in traces and planes to
answer that question. It would be great if we could see mag fields!

There is mag field viewing film. And you can make your own viewer by dropping iron filings in a shampoo bottle. Crude but I've seen it demoed and work.


NT

 

On Monday, 20 May 2019 05:55:59 UTC+1, tabby wrote:

On Sunday, 19 May 2019 22:48:13 UTC+1, John Larkin wrote:
On Sun, 19 May 2019 14:22:57 -0700 (PDT), dagmargoodboat@yahoo.com

wrote:

I had two cases in a row recently of many-layer power-planed
boards with power supplies that wouldn't come up above a diode
drop, and I was able to use a trick devised for the first one to
solve the problem on the second one, too --

I set a current-limited supply to ~30mA & left the board
to stabilize thermally. I then looked for the 'hot' parts
with an IR thermometer. Worked like a charm.

Temp. rise was about 1oC @ 20mW. The IR thermometer? $14
well-spent.


Cheers,
James Arthur

Thermal imagers are getting affordable and are great to have around.
Not only can they find shorts and bad parts, it's good to image a new
design and see if anything runs hot.

https://www.dropbox.com/s/mlaf2yce2z3xiv7/IR_0025.jpg?dl=0

https://www.dropbox.com/s/r4q2z8vnonwh4mc/IR_Board.jpg?dl=0

Our test people use a thermal imager too, to spot unusual stuff.

One eternal problem is electronics is "where is the current going?"

Sometimes you can measure microvolt drops in traces and planes to
answer that question. It would be great if we could see mag fields!

There is mag field viewing film. And you can make your own viewer by dropping iron filings in a shampoo bottle. Crude but I've seen it demoed and work.


NT

oops, baby oil not shampoo


NT

 

[Bill Sloman]

On Monday, May 20, 2019 at 7:23:02 AM UTC+10, dagmarg...@yahoo.com wrote:

I had two cases in a row recently of many-layer power-planed
boards with power supplies that wouldn't come up above a diode
drop, and I was able to use a trick devised for the first one to
solve the problem on the second one, too --

I set a current-limited supply to ~30mA & left the board
to stabilize thermally. I then looked for the 'hot' parts
with an IR thermometer. Worked like a charm.

Temp. rise was about 1oC @ 20mW. The IR thermometer? $14
well-spent.

Microvolt sensitive DVM's are cheaper, if not as quick. Any power trace that show a voltage drop points to the short, so it doesn't take long to get it localised. And you don't have to wait for the board to warm up.

--
Bill Sloman, Sydney

 

[Mike]

On 5/19/2019 9:55 PM, tabbypurr@gmail.com wrote:

On Sunday, 19 May 2019 22:48:13 UTC+1, John Larkin wrote:
On Sun, 19 May 2019 14:22:57 -0700 (PDT), dagmargoodboat@yahoo.com

wrote:

I had two cases in a row recently of many-layer power-planed
boards with power supplies that wouldn't come up above a diode
drop, and I was able to use a trick devised for the first one to
solve the problem on the second one, too --

I set a current-limited supply to ~30mA & left the board
to stabilize thermally. I then looked for the 'hot' parts
with an IR thermometer. Worked like a charm.

Temp. rise was about 1oC @ 20mW. The IR thermometer? $14
well-spent.


Cheers,
James Arthur

Thermal imagers are getting affordable and are great to have around.
Not only can they find shorts and bad parts, it's good to image a new
design and see if anything runs hot.

https://www.dropbox.com/s/mlaf2yce2z3xiv7/IR_0025.jpg?dl=0

https://www.dropbox.com/s/r4q2z8vnonwh4mc/IR_Board.jpg?dl=0

Our test people use a thermal imager too, to spot unusual stuff.

One eternal problem is electronics is "where is the current going?"

Sometimes you can measure microvolt drops in traces and planes to
answer that question. It would be great if we could see mag fields!

There is mag field viewing film. And you can make your own viewer by dropping iron filings in a shampoo bottle. Crude but I've seen it demoed and work.


NT

HP made an AC current probe/tracer.
In combination with the pulser, you can lay it on a trace and determine
which way the current goes with the tracer.
Easy on outer layers. Not so easy on inner layers or with multiple
ground planes in the way.


Thermal imager is easier...and a good excuse to buy a new toy.

 

[gregz]

<tabbypurr@gmail.com> wrote:

On Sunday, 19 May 2019 22:48:13 UTC+1, John Larkin wrote:
On Sun, 19 May 2019 14:22:57 -0700 (PDT), dagmargoodboat@yahoo.com

wrote:

I had two cases in a row recently of many-layer power-planed
boards with power supplies that wouldn't come up above a diode
drop, and I was able to use a trick devised for the first one to
solve the problem on the second one, too --

I set a current-limited supply to ~30mA & left the board
to stabilize thermally. I then looked for the 'hot' parts
with an IR thermometer. Worked like a charm.

Temp. rise was about 1oC @ 20mW. The IR thermometer? $14
well-spent.


Cheers,
James Arthur

Thermal imagers are getting affordable and are great to have around.
Not only can they find shorts and bad parts, it's good to image a new
design and see if anything runs hot.

https://www.dropbox.com/s/mlaf2yce2z3xiv7/IR_0025.jpg?dl=0

https://www.dropbox.com/s/r4q2z8vnonwh4mc/IR_Board.jpg?dl=0

Our test people use a thermal imager too, to spot unusual stuff.

One eternal problem is electronics is "where is the current going?"

Sometimes you can measure microvolt drops in traces and planes to
answer that question. It would be great if we could see mag fields!

There is mag field viewing film. And you can make your own viewer by
dropping iron filings in a shampoo bottle. Crude but I've seen it demoed and work.


NT

I had used a Tektronix DC current probe at one point in time to follow
current.

Greg

 

[whit3rd]

On Sunday, May 19, 2019 at 2:48:13 PM UTC-7, John Larkin wrote:

>...It would be great if we could see mag fields!

It can be done. The old Kyread solution (spray=on to floppies or
mag tape, it shows the tracks) is one way

<https://www.magneticdeveloper.com>

and ferrofluid is another. The sheet gizmos (actually a lot of microspheres with loose
grains inside) are fun to play with, but only old 8" floppies have coarse
enough tracks to show up on those.

 

[Jeroen Belleman]

whit3rd wrote:

On Sunday, May 19, 2019 at 2:48:13 PM UTC-7, John Larkin wrote:

...It would be great if we could see mag fields!

It can be done. The old Kyread solution (spray=on to floppies or
mag tape, it shows the tracks) is one way

https://www.magneticdeveloper.com

and ferrofluid is another. The sheet gizmos (actually a lot of microspheres with loose
grains inside) are fun to play with, but only old 8" floppies have coarse
enough tracks to show up on those.

I'd have to be really desperate before I'd apply any kind
of goo to my circuit board to find a short. I've always
homed in on the short by following the voltage gradient
with a sensitive voltmeter. It's easy if the current flows
in discrete tracks, but I've also found hard shorts between
full power planes on big boards full of ECL logic that way.

Jeroen Belleman

 

[George Herold]

On Monday, May 20, 2019 at 8:00:37 AM UTC-4, Jeroen Belleman wrote:

whit3rd wrote:
On Sunday, May 19, 2019 at 2:48:13 PM UTC-7, John Larkin wrote:

...It would be great if we could see mag fields!

It can be done. The old Kyread solution (spray=on to floppies or
mag tape, it shows the tracks) is one way

https://www.magneticdeveloper.com

and ferrofluid is another. The sheet gizmos (actually a lot of microspheres with loose
grains inside) are fun to play with, but only old 8" floppies have coarse
enough tracks to show up on those.

I'd have to be really desperate before I'd apply any kind
of goo to my circuit board to find a short. I've always
homed in on the short by following the voltage gradient
with a sensitive voltmeter. It's easy if the current flows
in discrete tracks, but I've also found hard shorts between
full power planes on big boards full of ECL logic that way.

Jeroen Belleman

Right that's what I do, (measure DC mV with ~20 mA of current)
My power supply tends to look dendritic and I don't know how well the DC
trick works with power planes.

George H.

 

[John Larkin]

On Mon, 20 May 2019 05:46:14 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Monday, May 20, 2019 at 8:00:37 AM UTC-4, Jeroen Belleman wrote:
whit3rd wrote:
On Sunday, May 19, 2019 at 2:48:13 PM UTC-7, John Larkin wrote:

...It would be great if we could see mag fields!

It can be done. The old Kyread solution (spray=on to floppies or
mag tape, it shows the tracks) is one way

https://www.magneticdeveloper.com

and ferrofluid is another. The sheet gizmos (actually a lot of microspheres with loose
grains inside) are fun to play with, but only old 8" floppies have coarse
enough tracks to show up on those.

I'd have to be really desperate before I'd apply any kind
of goo to my circuit board to find a short. I've always
homed in on the short by following the voltage gradient
with a sensitive voltmeter. It's easy if the current flows
in discrete tracks, but I've also found hard shorts between
full power planes on big boards full of ECL logic that way.

Jeroen Belleman

Right that's what I do, (measure DC mV with ~20 mA of current)
My power supply tends to look dendritic and I don't know how well the DC
trick works with power planes.

George H.

A real short can stand an amp or more of current. A 1oz copper sheet
is about 500 uohms per square so you get lots of signal. The polarity
and voltage pattern can lead you to a short.

If you order 1 oz copper, you'll rarely get 1 oz, so there's even more
voltage!

We have all our PCBs bare-board tested, so we don't see PCB internal
shorts any more.

Lately I put a 0.1 ohm resistor in series with every voltage
regulator, so I can snoop supply currents. That has lots of uses.

The mag fields would be milligauss, way too low for iron filing sorts
of tricks.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Martin Rid]

dagmargoodboat@yahoo.com Wrote in message:
> I had two cases in a row recently of many-layer power-planedboards with power supplies that wouldn't come up above a diodedrop, and I was able to use a trick devised for the first one tosolve the problem on the second one, too --I set a current-limited supply to ~30mA & left the boardto stabilize thermally. I then looked for the 'hot' partswith an IR thermometer. Worked like a charm.Temp. rise was about 1oC @ 20mW. The IR thermometer? $14well-spent.Cheers,James Arthur

I remember the Shortsqueak. Like a logic probe. Worked on
resistance, and changed pitch as you got closer to the short. I
think Nuts&volts had something similar too.
Cheers

--


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

 

On Monday, May 20, 2019 at 2:04:21 AM UTC-4, Bill Sloman wrote:

On Monday, May 20, 2019 at 7:23:02 AM UTC+10, dagmarg...@yahoo.com wrote:
I had two cases in a row recently of many-layer power-planed
boards with power supplies that wouldn't come up above a diode
drop, and I was able to use a trick devised for the first one to
solve the problem on the second one, too --

I set a current-limited supply to ~30mA & left the board
to stabilize thermally. I then looked for the 'hot' parts
with an IR thermometer. Worked like a charm.

Temp. rise was about 1oC @ 20mW. The IR thermometer? $14
well-spent.

Microvolt sensitive DVM's are cheaper, if not as quick. Any power trace that show a voltage drop points to the short, so it doesn't take long to get it localised. And you don't have to wait for the board to warm up.

--
Bill Sloman, Sydney

But a microvolt DVM can't track down a diode-to-ground, which was the
problem.

Cheers,
James Arthur

 

On Sunday, May 19, 2019 at 8:05:07 PM UTC-4, Tom Del Rosso wrote:

John Larkin wrote:

Thermal imagers are getting affordable and are great to have around.
Not only can they find shorts and bad parts, it's good to image a new
design and see if anything runs hot.

But the cheap ones have low res. What do you think is minimum useful
res?

One pixel worked decently well for me. <g>

YMMV.

Cheers,
James Arthur