Re: Overclocking in Dell

From: Brian (brian_at_beepbeep.invalid)
Date: 10/08/05 

Date: Sat, 08 Oct 2005 13:19:02 +0100

On Sat, 08 Oct 2005 02:37:24 +0000, Michael Black wrote:

>
> Brian (brian@beepbeep.invalid) writes:
>> On Fri, 07 Oct 2005 18:28:50 -0500, John Hasler wrote:
>>
>>> Poly-poly man writes:
>>>> I know; I have exploded a monitor with incorrect settings.
>>>
>>> This is no longer possible with modern monitors.
>>>
>> Quite.
>> I don't think it was even possible 10 years ago, except maybe on monitors
>> made by Urban Myth, Inc.
>>
> IN a monitor (or a tv set for that matter), the high voltage is generated
> by the horizontal sync signals.
>
Yep, I know. For my sins, I once repaired TVs/monitors.

> The horizontal deflection chain traditionally is designed for a very
> small range of frequencies. Move out of that range, and the horizontal
> deflection transistor can burn out because it's being asked to do more
> than it can. Some of the other components can go with it.
>
More a case that the frequencies it's happily following allow the HT
generating circuitry to oscillate at a higher frequency - usually at some
peak response outside the design range, which in the process consumes a
higher current and generates a corresponding increase in the HT - either
of which normally provide brief but spectacular effects.
It was once a fun pastime to occasionally sacrifice otherwise dead
monitors/TVs by deliberately driving the lightly modified line output
circuitry at some insane frequency, with the aim of generating a Jacob's
Ladder effect of a high-voltage arc travelling up the space between a
couple of brass rods - one earthed, one connected to the HT output of the
line transformer. Think of almost any "Frankenstein's lab" type of movie
and you'll have seen it.

But this assumes that the line sync present on the input is the sole
source of the line frequency used inside the monitor and from my
experiences, it's only used to synchronize a free-running oscillator which
left unattended, runs at or near the intended frequency. Otherwise things
could be auto-toasting just as soon as the input sync vanished (unplug
video cable, switch PC off first etc.) and the oscillator wandered off
doing its own thing.

So I'd take the "very small range of frequencies" to refer to a small
range of frequencies that the monitor's line oscillator would reliably
synchronize to (the design range) before it becomes so out of range as to
effectively become no signal at all - at which point the oscillator just
resorts to free-running at/near the intended frequency.

> The 6845 that was common in older computers (and right into the "IBM PC"
> age until the video boards got higher integration) was a programmable
> device, allowing one to output all kinds of sync frequencies.
>
A very useful chip, for its time. I used it on a couple of projects.

> Combine that flexibility with a fixed rate monitor, and yes, you
> did risk doing damage. Put the wrong values into the video generator,
> and the monitor couldn't keep up, and things start smoking.
>
I can't think of any instances where this has actually happened, although
I can see how it might with some of the /very/ early monochrome monitors
which arrived with the first floods of IBM-PC "clone" machines.
Some of those were very nasty with poor quality circuit design/components,
foul quality displays and were inherently unreliable anyway, never mind
problems caused by wayward sync frequencies. ;)

> And given how "smart" monitors have become
>
Yes - definitely much preferable to have a display saying "Signal out of
range" or somesuch instead of a mysterious blank screen. Many will even
display the frequencies in use, when asked - a much happier state of
affairs.

B. 

-- 
Time is what keeps everything from happening at once.

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