Death by Poking

From: Ethan Dicks <>
Date: Thu Jan 18 00:03:57 2001

--- John Lawson <> wrote:
> Basically, the yoke coil is calculated to 'ring' at a certain frequency...
> ...The circuit is designed so that at that freq, the yoke is in resonance,
> and therefore uses less current to get the job done; hence less wire and
> lighter, cheaper parts... it begins to draw large amounts of power trying to
> do the same work, and, in a lot of the 'cheap' monitors, the whole thing
> actually overheats and burns up while you are looking at the jagged lines
> and trying to figure out what to do next.

We lost a 19" Dell monitor (not cheap) at work last year when our Webguy
punched in an unfortunate refresh rate and didn't hit test first. I wasn't
there at the time, but my two buddies in IT who were in his cube (but facing
away at the time) said the flash was impressive.

> ALSO: Long ago in the Big Iron days... the were some machines in the
> Philco line whose power supplies in some configs were marginally
> inadequate. It was possible to load the machine (with programs and data)
> and trip (or burn) the power units...

I heard about someone who disassembled a "worst-case" memory diagnostic for
some DEC machine with core, perhaps the PDP-8, perhaps some other 1960's
model. He calculated that the program did not, in fact, perform a worst-
case test for memory access/data loss. He described his ideas to improve
the program to a Digit (DEC employee) who was familiar with the hardware
and software in question. The curious customer was warned against implementing
his idea because it was already known that a true worst-case scenario would
result in too much current being drawn through the core stack, causing
serious thermal problems if left to run for extended periods of time.

Also, there were programs in the days if Big Iron to abuse hardware built
with a particular duty cycle in mind, print hammers coming to mind. One
I was told about by the perpetrator was simple and fiendish - he analyzed
the pattern of letters on the band and devised a print line that caused all
the hammers to trip at once, rather than the usual 10%-20% that fired when
ordinary text was printed. The resulting current drain from a relatively
small number of lines of this, fried the power supply.

Then there's the practice of writing disk diagnostics that take advantage
of harmonic oscillations when the drive's voice coil is slammed from inner
to outer track, causing the drive to walk across the room. There are stories
of this happening entirely due to heavy usage and disk thrashing, not just
college pranksters seeing what the limits of physics are.

Disks that weight one kg. and inkjet printers just aren't as much fun as the
older stuff, one might think.


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Received on Thu Jan 18 2001 - 00:03:57 GMT

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