Re: tempest PCB only some vectors shaky

For what it's worth, I've tried using my Tek digital scope to view the
output of Star Wars and Tempest on that LCD and it looked horrible,
about what it looks like on your image. Using an analog scope with a
CRT has been the only suitable replacement for a monitor for my
testing purposes.

As Andy said, you may be chasing your tail unless you see an actual
problem when using a real vector monitor.

Joel
Sent from my iPhone

On Jun 6, 2012, at 7:47 AM, Andrew Welburn <andy@andysarcade.net> wrote:

> 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 09:25:57 2012