Re: tempest PCB only some vectors shaky

Thanks for the response. I probably wasn't clear enough in my
explanation. In the real game (PS + PCB + WG6100) some vectors are rock
solid and other vectors jitter by a few mm on-screen. I don't own a video
camera that is able to record a first-hand view.

I used the oscilloscope for two purposes. First it helps to diagnose if the
problem is coming from the PCB or the monitor; since the PCB testpoints
demonstrate the problem, before it even hits the monitor, I can be
confident that the monitor isn't involved. Second the oscilloscope is
configured for persistence and shows that one stroke is dead-on while the
other stroke varies by maybe 100mV. Capturing 1 second of screen refresh
with a test-pattern was my best idea to demonstrate how the stroke varies
over time.

And to double clarify -- as far as I've seen, for an individual refresh
frame, the strokes are not stair-stepped or fuzzy. Image is fuzzy on the
oscilloscope because it's overlaying the past 1sec of refreshes. On an XY
the phosphor fades quicker so this looks like a shake; sometimes the line
is drawn a little higher, sometimes a bit lower.

Right now I'm thinking the positive-slope versus negative-slope is a hint.
I don't know which direction the beam is drawing but maybe the signal is
noisier when it's slewing upward versus downwards. Perhaps the old
capacitors are less consistent when charging or discharging? Also
considering the 1495s since they're introducing BIP and LIN.

-joey

On Wed, Jun 6, 2012 at 5:42 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/**CYke3MLZ4e94Cf5vb2UUPkuaTiHWm1*
>> *2LLNxmPUaffgU?feat=directlink<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 10:58:39 2012