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Reply-To: "fred bartoli"
From: "fred bartoli"
Subject: Re: *standard* VGA sync levels ?
Date: Mon, 2 Dec 2002 11:41:01 +0100
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NNTP-Posting-Date: 02 Dec 2002 11:38:18 MET
a écrit dans le message :
> fred bartoli wrote:
> > Hello,
> > The fire brigade (I) have to design some protective device (will be a
> > of dongle) that will be insterted between the video output and the
> > cable to prevent a badly designed video output (our nice work) to
> > latchup in fields (about 5% every two weeks... eh eh, not so bad).
> A badly designed video signal would not cause lockup, with any moderately
> recent monitor.
> It may well cause it to go into self-protect, and stop displaying stuff.
> What do you mean by latchup?
By latchup I mean latchup. My pb isn't a monitor one but a video CRT
controler pb, i.e. from parasitics *incoming* signals.
Due to the use of an external monitor (separate PSUs with the "computer
side"), the lack of protections (or use of rather symbolic ones) and a
stupid "nice wiring advice" provided in the appnote of the CRT controler,
the CRT video controler outputs goes latchup on some mains transients
Just for information, the weird advice given in the appnote is to separate
the chip DAC-GND region from the DIGITAL-GLOBAL-GND side with a 1.5uH
inductor, probably to provide a "quiet ground" for the video output. This
was nicely over-done by the board disgner who "improved" the inductor value
changing it to 4.7uH. The net result is that on common mode transients
between the CRT and the video controler, the video chip has its DAC-GND
region biased wrt the normal GND zone.
Of course, thousands of boards already dispersed everywhere...
> http://inquisitor.i.am/ | mailto:email@example.com | Ian
> "I am the Emperor, and I want dumplings." - Austrian Emperor,
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