On Wednesday 10 February 2010, te...@cnysupport.com wrote:
>Quoting jd <onymo...@garlic.com>:
>> Kurt Buff さんは書きました:
>>> Uh, paranoia is not mitigated by ignorance. Remember the earlier
>>> description of her friend: retired and partially disabled. This
>>> probably means older and not nearly as educated as we are about
>>> computers, and set in his/her ways. This, augmented by scare
>
>stories
>
>>> in the mass media, probably contribute to the difficulty.
>>
>> A lot of older people still believe that giving the PC the wrong
>> command will cause it to explode in a shower of sparks, thanks to
>> Hollywood. It seems that Hollywood is still doing that.
>>
>> I can't count how many times my boss's boss would yell at me when a
>
>PC
>
>> quit working, afraid I'd given it some command that would cause it
>> to explode.
>
>While explosions aren't a big problem, smoke and damage was completely
>possible.
>
>Back in the "olden days" before flat panel displays and smart CRTs, it
>was entirely possible to select a refresh rate or resolution that
>would cause a monitor to smoke and die.
>
>AFAIK, this is not possible with current hardware.
>
>Terry
>
True, but X's paranoia lives on. I have preached before, but perhaps not to
this choir.
If you enjoy a good rant, by someone who has been there and done that, read
on.
The grand and glorious failures generally occurred 20-10 years ago for the
most part. The usual cause was trying to run the monitors at a lower scan
rate than they had transformer iron to handle. Generally speaking this is
very very rarely a vertical sweep problem, for 2 reasons, but first &
foremost, those transformers were iron cored, and because of that had a much
softer saturation failure than the highly tuned ferrite cores used in the
horizontal scan (and high voltage) circuits. There, the sweep currant
amplitude determines the width, but that amplitude delivered to the coils of
the deflection yoke is determined by the rate of rise or fall of the current
in the transformer. The width is now regulated, usually by adjusting the
supply voltage downward at the lower sweep frequencies.
However, the slower sweep rates, because this is a 'velocity' to amplitude
conversion, allows the current in the transformer to rise for a longer period
of time before its turned off & reversed to retrace the beam to the left side
of the CRT. If this current is allowed to rise for long enough, the ferrite
core will become saturated, which is a fancy way of saying the core no longer
has an influence on the circuit inductance, and the effective inductance is
then no more than if the core had been physically removed. The rate of
current rise is then largely un-impeded and can rise many tens of amps per
microsecond, quite high by the time the transistor's drive is removed and it
_tries_ to turn off. Junction temps in the transistor rise until it
explodes, usually blowing bits of epoxy-B off the top. Correspondingly
during this same time frame, the circulating currents cause the supplies
capacitors to overheat, and occasionally those electrolytics will vent, or at
least push the tops up into a definite dome shape.
A similar effect can also be triggered by heat in that ferrite core. Most
ferrite mixes have a quite low 'curie' point, often below 100C! The 'curie'
point is that point in the process of heating an iron alloy, where the iron
loses its magnetic properties. So at temp X, the ferrite disappears from the
magnetic circuit, and like steel, if cooled quickly enough, will not regain
those magnetic properties ever again. Its still steel, or in this case
ferrite, but you cannot pick it up with a magnet. Exhaust valves in lots of
engines have been made from it since WW-II times, its then called Austenitic
(SP?) steel.
All this because somebody replaced an ega rated monitor that could run at
22khz, with a vga rated one that was designed to run at a minimum of 31khz,
and their card could only muster up 28khz. The results were predictable, a
failure, the only question was how long it took. And it was a big enough
problem for the monitor makers that they were quickly fitted with protective
circuitry. So that is not now a problem in terms of being a fire hazard and
has not been for much of a decade now.
Conversely, going the other way, at the top end, the power supply runs out of
headroom, the high voltage gets soft, the pix narrower and probably dimmer,
but generally speaking a 70khz rated monitor will not be damaged by a 90khz
drive. Similarly, a 15khz rated monitor is not damaged, even on a long term
basis, by running it at 19 khz, I have been doing that for many years on what
this group would definitely call a 'legacy computer', a TRS-80 Color Computer
3. It is, when its hooked up, the second, fully independent monitor I can
use.
So, IMNSHO, X is way overdue to lose that paranoia, the monitor folks fixed
that problem nearly a decade ago. They (X) are trying to protect the user
from a situation that no longer exists in 99.999% of the environment.
More trivia, lots more, than you wanted to know I'm sure. ;-)
Joanne could confirm this, but she has more respect for the lists topic, I
think...
Me, I get interested when the topic drifts away in my direction of knowledge.
My apologies in this case would be somewhat less than sincere.
Now, back to your regularly scheduled discussions. Spamassassin I believe it
was. ;)
--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
One tree to rule them all,
One tree to find them,
One tree to bring them all,
and to itself bind them.
-- Gavin Koch <ga...@cygnus.com>
