IEEE Spectrum September, 2008 - 19

tools&toys
The Voltage in the Dell

A mysterious current led me to the perfect
multipurpose monitor

I

just can't squeeze two
screens into my living-room
home office, sharing it as I
do with two small boys, their
train sets and games, and
a tank full of aquatic frogs.
So last year I sought out
one display that would do
everything. My seemingly
simple search turned into
an engineering detective
story that would ultimately
involve three companies,
four monitors, a helpful
executive, and a tutorial on
the nature of electric current.
It wasn't much of a quest
at first: I quickly settled
on a US $999 27-inch Dell
2707WFP with decent
resolution, which I could
plug my digital cable box
directly into. Then I noticed
horizontal pink bands that
moved slowly through the
television picture. The
problem stumped customer
service at both Dell and Time
Warner Cable. Still, Dell
swapped the monitor three
times. Time Warner changed
my set-top box and then
my cables. Nothing worked.
It was time for Google.
I searched on "slow pink
bars" and found my problem:
a ground loop-the same
condition that causes a
loud hum in some stereo
equipment. When there are
small voltage differences
in the wiring that connects
different pieces of electrical
equipment, an unintended
current will flow through
the system. In my case it ran
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through a printed circuit
board within the monitor,
showing as slow-moving
bands called hum bars,
which are sometimes pink.
With my diagnosis, I also
found Jensen Transformers,
in Chatsworth, Calif., known
throughout the Internet
as the king of ground-loop
fixers. Jensen sold me a
$60 ground-loop isolator that
attached to my television
cable. It worked, but it also
blocked the kids' cable
cartoon channels. Jensen
sent another model of isolator
that had the same problem.
Not giving up, the company
sent-at its own expense-
a $500 "humbucker." When
that didn't work, Jensen's
president, Bill Whitlock,
called to take me on a stepby-step test to find the exact
point in my system where
the pink gremlins were
invading. He also told me
that a properly designed
monitor would have routed
the ground hum away
from the video circuitry.
Visible bars were evidence
of what he called a "headslapping design flaw."
Whitlock wondered
aloud whether anyone
teaches ground loops in
engineering schools these
days. Designers, he says,
apparently come out of
places like MIT thinking
that ground wire equals
zero current, end of story.
Most designers don't know
that they can build a $15 test

device that would vastly
improve their designs.
I called Dell once again.
The company generously
responded with an upgrade
to a far better monitor-
the 3008WFP, a 30-inch
model that had come out just
two weeks earlier and costs
twice as much as my original.
Its resolution is so good I
can keep five or six windows
open at once. It also doubles
as a true HD 1080 television.
Last year, the only
monitors with 4-megapixel
(2560-by-1600) resolution
were designed strictly for
doctors and graphics artists.
They were expensive, yet
didn't easily replace a TV,
having only a single digital
visual interface (DVI)
input. This year, however,
Dell realized that a simple
modification would make its
highest-end monitor ideal for
video gaming and plain old
television watching as well
as computing. Dell gave it
seven inputs in all, including
high-definition multimedia
interface, display port, DVI,
component video (the familiar
triad of red, green, and blue
plugs), and composite video
(using a single yellow RCA

Pink hum bars, visible in the
white lettering above, proved
a nearly intractable problem
in one Dell monitor model.
Photo-iLLustration: hum bars: biLL WhitLocK;
monitor: DeLL

connector). The picture is so
crisp, and the colors so vivid,
that the 3008 has become
the kids' favorite set. In fact,
they complain bitterly when
Mom takes it back for her
obsessive multitasking.
All this technology
doesn't come cheap. The
monitor itself costs
about $1964, and for peak
resolution you need a highend graphics card. And
this is, of course, television
without a tuner and without
built-in sound. Add a
cable or satellite box and
external speakers, though,
and it's good to go.
Would I buy one next
time around? For me the
3008 is absolutely worth the
full freight. If a television is
all you're looking for, you
can get a 42-inch high-end
set for the same money. But
if you want one screen that
does it all and does it very
well, it's worth going into the
red. Just stay out of the pink.
-Sherry Sontag

september 2008 * Ieee spectrum * NA

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Table of Contents for the Digital Edition of IEEE Spectrum September, 2008
