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'[EE] Noisy Dell laptop supply?'
2005\12\15@164752 by Mike Hord

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Medium-to-long explanation follows this executive summary:

Has anyone noticed any noise issues related to Dell laptop
power supplies?

Full story:

I'm working with meidum precision analog signals-
16 bit (hopefully).  We were noticing intermittent noise in
the output, which was usually present.  The acquistion
system is connected to the computer via vanilla serial
(no USB adapter, just a port on the laptop).  Finally, the
noise can be eliminated by unplugging the supply from
the laptop.  Unplugging the supply from the wall doesn't
help, only unplugging the supply from the laptop.

The long-term solution is optical isolation, but I'm curious
as to whether this is something others have encountered.

We haven't tried connecting it to other PCs yet, as we
don't have any on hand for testing.  I did notice a similar
problem with my newer model Inspiron- terrible noise
when I connect to my stereo for listening to music.

Mike H.

2005\12\15@170501 by Daniel Gliebe

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I too have noticed this when connecting my Dell Inspiron 9100 to the TV
to watch videos.  The audio is absoultly horrible.  If I disconnect the
power supply from the laptop all noise stops.
If anybody has solutions to fix this problem I'm all ears.

  -Dan


Mike Hord wrote:

{Quote hidden}

2005\12\15@172932 by Mike Hord

picon face
> I too have noticed this when connecting my Dell Inspiron 9100 to the TV
> to watch videos.  The audio is absoultly horrible.  If I disconnect the
> power supply from the laptop all noise stops.
> If anybody has solutions to fix this problem I'm all ears.

Cheater plug- something that bypasses the ground.  Fixes it right up.
Doesn't work on my other problem, though.

I have an Inspiron 9100 as well.  It'll be the last Dell that I buy or that I
let anyone else I know buy.  It sits on my coffee table almost all the
time (as in, gets moved less than once a month) and yet has still had
more failures than reasonable:  I have my second replacement
motherboard at home right now, I've replaced the graphics card, the
optical drive, and the AC adapter.  It has never given me above what
I would consider mediocre performance.

Mike H.

2005\12\15@173035 by Mark Rages

face picon face
On 12/15/05, Mike Hord <spam_OUTmike.hordTakeThisOuTspamgmail.com> wrote:
> Medium-to-long explanation follows this executive summary:
>
> Has anyone noticed any noise issues related to Dell laptop
> power supplies?
>
> Full story:
>
> I'm working with meidum precision analog signals-
> 16 bit (hopefully).  We were noticing intermittent noise in
> the output, which was usually present.  The acquistion
> system is connected to the computer via vanilla serial
> (no USB adapter, just a port on the laptop).  Finally, the
> noise can be eliminated by unplugging the supply from
> the laptop.  Unplugging the supply from the wall doesn't
> help, only unplugging the supply from the laptop.
>

Sounds like a ground loop, except for the "Unplugging the supply from
the wall doesn't help" part.  Are you physically pulling the plug from
the wall or just shutting off a power strip?

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2005\12\15@174317 by Mike Hord
picon face
> Sounds like a ground loop, except for the "Unplugging the supply from
> the wall doesn't help" part.  Are you physically pulling the plug from
> the wall or just shutting off a power strip?

Physically removing the plug from the wall.

Ground loop is SUPREMELY unlikely, as the acquisition unit (I should
have mentioned this) is running on a 9V battery.

Mike H.

2005\12\15@213658 by Bob Ammerman

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> I have an Inspiron 9100 as well.  It'll be the last Dell that I buy or
> that I
> let anyone else I know buy.  It sits on my coffee table almost all the
> time (as in, gets moved less than once a month) and yet has still had
> more failures than reasonable:  I have my second replacement
> motherboard at home right now, I've replaced the graphics card, the
> optical drive, and the AC adapter.  It has never given me above what
> I would consider mediocre performance.
>
> Mike H.


FWIW:

I am now on my third Dell Inspiron Laptop, each of which I have used for
three years before retiring it to get a faster one.

Inspiron 7000 - 15"  1024x768 - 300MHz Pentium II, 30GB 4200RPM, 250MB RAM
Inspiron 8100 - 15.4" 1600x1200 - 1GHz Pentium III, 40GB 4200RPM, 512MB RAM
Inspiron 9200 - 17" 1920x1200 - 2GHz Pentium M, 60GB 7200RPM, 1GB RAM

So, my next machine should be:

Inspiron 10300 - 18" 2496x1560 - 4GHz Pentium ? (64 bit!), 100GB 7200RPM,
2GB RAM  ;-)

I have been very pleased with all three machines. They have been my 'daily
drivers' and I drag them around to customer sites almost every day. I do
purchase Dell's 'Complete Care' on them, and I have gotten my money out of
it each time (so far the 9200 has had zero problems except a power cord
issue).

Bob Ammerman
RAm Systems


2005\12\16@021451 by Morgan Olsson

flavicon
face
Also the screen can make lots of EMI.  Probably the backlight.
One customer had a laptop that radiated enourmously from the back of the screen, enought to make his picologic data logger measure horribly wrong.
(Teeese Picologic are toys, BTW :( )
/Morgan
--
Morgan Olsson, Kivik, Sweden

2005\12\16@080638 by Gerhard Fiedler

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Mike Hord wrote:

> Ground loop is SUPREMELY unlikely, as the acquisition unit (I should
> have mentioned this) is running on a 9V battery.

Where is it connected to?

Gerhard

2005\12\16@085507 by Alan B. Pearce

face picon face
>I am now on my third Dell Inspiron Laptop, each of
>which I have used for three years before retiring
>it to get a faster one.
>
>Inspiron 7000 - 15"  1024x768 - 300MHz Pentium II, 30GB 4200RPM, 250MB RAM
>Inspiron 8100 - 15.4" 1600x1200 - 1GHz Pentium III, 40GB 4200RPM, 512MB RAM
>Inspiron 9200 - 17" 1920x1200 - 2GHz Pentium M, 60GB 7200RPM, 1GB RAM

I have an Inspiron 8600 1920x1200 which has been faultless (except I broke
the power supply by shorting the centre pin to the inner barrel - after that
it wouldn't charge because it could no longer ID the supply).

>So, my next machine should be:
>
>Inspiron 10300 - 18" 2496x1560 - 4GHz Pentium ? (64 bit!), 100GB 7200RPM,
>2GB RAM  ;-)

In a laptop? wow ...

>I have been very pleased with all three machines.

I also have a desk top machine at home. Both have been great machines.

Note that the power supply ID is done by a 1-pin Dallas device. I wonder if
the laptop keeps interrogating that even if the supply is not powered up,
and that is what is causing the noise?


2005\12\16@115359 by Mike Hord

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>From Gerhard-

> > Ground loop is SUPREMELY unlikely, as the acquisition unit (I should
> > have mentioned this) is running on a 9V battery.
>
> Where is it connected to?

The device it connects to is a free-standing battery powered device
which is immersed in a tank of water, monitoring the temp and
oxygenation of the tank.  The tank is isolated- it's acrylic, so it
isn't conductive, and the circulation pump is a standard aquarium
type sealed pump.

>From Alan-

> Note that the power supply ID is done by a 1-pin Dallas device. I wonder if
> the laptop keeps interrogating that even if the supply is not powered up,
> and that is what is causing the noise?

An intriguing possibility.  The other thing we've considered is that the thing
just behaves as a great, long antenna, picking up noise from the battery
chargers and refrigerator and so on in close vicinity to the whole affair.

Some sort of optical isolation seems to be likely in the near future, though.

Mike H.

2005\12\16@124651 by Peter

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On Fri, 16 Dec 2005, Morgan Olsson wrote:

> Also the screen can make lots of EMI.  Probably the backlight. One
> customer had a laptop that radiated enourmously from the back of the
> screen, enought to make his picologic data logger measure horribly
> wrong. (Teeese Picologic are toys, BTW :( ) /Morgan -- Morgan Olsson,
> Kivik, Sweden

I agree. One of the first things I do when working with a laptop on the
workbench is to put a scope against the plastic back of the display and
sniff with it around the hinge. Sometimes the results can be very
surprising. I have often glued insulated copper sheet behind the
display, and grounded it, for this reason. It helps a lot. Of course
hash from the smpsu will kill anything rf that is reasonably sensitive.

Peter

2005\12\16@125433 by Peter

picon face

Mike Hord wrote:

> Ground loop is SUPREMELY unlikely, as the acquisition unit (I should
> have mentioned this) is running on a 9V battery.

Conducted noise from fast switching FET's drain ringing is far worse
than ground current. It is VHF to UHF and it gets into everything. The
inverse square law is almost the only available defence.

Peter

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