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Re: Will my graphics card support this?



On Sunday 31 December 2006 17:19, Ric Moore wrote:
>On Sun, 2006-12-31 at 20:39 +0800, Chong Yu Meng wrote:
>> On Fri, 2006-12-29 at 09:15 -0800, alan wrote:
>> > There is a modeline generation utility, but I cannot remember the
>> > name of it.  (My brain is still booting this morning.)
>>
>> xvidtune?
>
>Be careful as hell with xvidtune. It'll do whatever you merrily tell it
>to do. I blew the flyback out of a beautiful multisync back when a 15"
>model cost some large. I drove it just a teeny tiny itsy bitsy too much.
>ZING! <puff of smoke> That was a CRT monitor, BTW. I destroyed it
>dinking with it and xvidtune, cause I didn't know exactly what I was
>doing. That was one sad day. Ric

Your list resident C.E.T. speaks:

You didn't drive it too hard Ric, you drove it too slow, specifically the 
horizontal rate.  The design of an h-sweep circuit is a rather large 
balancing act, with the inductance of the sweep transformer often at the 
ragged edge of a saturated core when running at the usual lower end of a 
vga monitors range of 31 kilohertz.

The reason I mention saturated core is that at the lower end of the range, 
there is more time for the current through its primary winding to build 
up that must be turned off by the sweep transistor at the right edge of 
the screen.  When the core is not saturated, the inductance controls the 
rate of current rise and it might be 1.5 amps at that particular fraction 
of a microsecond, but if slowed down too much, (30khz is pushing your 
luck, 29khz maybe a few seconds, 28khz generally means toast in about a 
second) the rate of rise of the current will approach and hit the core 
saturation point, it can't hold any more magnetic field regardless of how 
much current flows, so the surplus field is ejected into the air around 
the core AND the inductance that controls the current disappears.  The 
currents can then rise from the 1 to 2 amp range it operates normally at, 
to 10 or 20 amps in the next microsecond.  The transistor cannot shut 
those current levels off at the right edge of the screen and survive for 
long, sometimes only milliseconds before it shorts out internally, and a 
lot of other parts are blown/burned in the process before the main 
shutdowns can operate, be they fuses or mechanical circuit breakers.

On the other end of the range, I've operated for many years an old NEC 5FG 
that's rated to go as high as 67khz, on a driver that merrily runs it at 
79khz while doing a 1600x1200 screen  The width and brightness perhaps 
may suffer, but its otherwise sharp and in perfect convergence today.  
The NEC 5FG had buckets of width overdrive, unlike this 19" Starlogic 
which is all run out at this same resolution and not filling the screen 
by about 1/8" on each side.

Anyway, that's an explanation, hopefully in understandable terms, of the 
probable cause as to why it made toast on you.

There are also several other failure mechanisms, usually related to 
partially failed electrolytic capacitors going un-noticed or ignored 
until the blowup, but those failures are going to happen even if its 
driven completely within its range ratings.  Those are related to heat 
and old age, and the quality of those capacitors in the first place.

-- 
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)
Yahoo.com and AOL/TW attorneys please note, additions to the above
message by Gene Heskett are:
Copyright 2006 by Maurice Eugene Heskett, all rights reserved.


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