Re: tempest PCB only some vectors shaky

For such a small problem, you are likely to be better off substituting
parts one at a time in the output section of X and Y, op-amps, switches,
dacs possibly. I have had any combination of these cause weird
abberations that you just can't find in the normal manner.

I'm betting its an op-amp, it feels like that sort of thing if you have
already replace all electrolytics.

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

On 06/06/2012 15:58, Joey Oravec wrote:
> 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
> <mailto: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 12:21:05 2012