Will my graphics card support this?

[Jim Cornette]

Gene Heskett wrote:
> 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.
> 

Thanks for the info Gene. The explanation seemed clear to me and quite 
detailed. Not a Certified Electronics Technician though.

Jim

-- 
Every young man should have a hobby: learning how to handle money is
the best one.
		-- Jack Hurley