Re: tempest PCB only some vectors shaky

  well, the problem we have of understaing is that you say the 'blue
line' and the 'red line' are different...

  I think you are trying to make it simpler to describe which line is
which by labeling them with colour.. but this has muddied your analysis
and description of the fault... One poster thinks you actually mean its
supposed to be red or blue. (they go on to assume incorrectly that
different colour lines are drawn by individual channels of hardware -
maybe they should at the bare minimum read some schems before comenting
*nudge* ;)

  The problem is, you're displaying the test screen on some LCD screen
based test equipment, very far removed from original hardware.

  I can tell you that the bottom left of your 'blue' line is where the
beam either starts drawing the screen frame or ends (inclined to sat
start). Looking at the other lines on your screenshot, i am seeing the
gradual fuzziness of some other lines, depending on how far they are
from the start point. I think this a gradual thing, but because the
start point is up against some lines near the end point, you are seeing
a high contrast in fuzziness.

  Personally, i think you are seeing a problem that isn't there, i think
its your test equipment and its display depth getting noisier toward the
end of the drawing frame.

Show us what it looks like on the real hardware, i'd put money on the
fact there's no problem at all.

Stop me if i'm wrong, but in the absence of any other response i think
this explanation fits.

Andrew Welburn
http://www.andys-arcade.com

On 05/06/2012 00:21, Joey Oravec wrote:
> Howdy -
>
> I'm trying to figure out why some, but not all, of the lines are shaky
> on my Tempest PCB. I set my oscilloscope to XY-mode with 1 sec persist
> and captured a screenshot. I'm not sure if it's allowed to send an
> attachment to the list, so here's a link:
>
> https://picasaweb.google.com/lh/photo/CYke3MLZ4e94Cf5vb2UUPkuaTiHWm12LLNxmPUaffgU?feat=directlink
>
> This is one corner of the diagonal line + alphabet self-test. Notice the
> blue line is solid but the red line is quite noisy. Predictably on the
> XY monitor the blue line is rock solid but the red line is shaky.
>
> I've already replaced the TL082s just in case. I don't suspect the DACs
> since the lines are both in the same corner and I'm not seeing
> stair-step error. Does anybody else have a theory of what makes those
> two lines different, and why one might be rock solid and the other one
> shaky?
>
> -joey
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Received on Wed Jun 6 07:46:27 2012