Asteroids with "dotted" lines

DogP

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Hey,

I booted up my Asteroids cabinet today, and while it played fine, I noticed that the graphics had faint dark lines through them, like it was being drawn with discrete dots... almost like playing on a color CRT with a shadow mask or something (mostly noticeable on moving objects like the asteroids). I quickly grabbed my DMM and checked the voltage... 5.05V at the chips, so probably OK.

To me, it looks like a PCB problem, not a monitor problem - but it'll be a few days before I get time to grab the scope and dig in. This is an Owl Eye Asteroids cabinet w/ G05-801 monitor, running the Braze Asteroids Multi. It claims to pass the self-test.

My initial impression is a bad LSb of both X and Y DACs, but that seems strange that both would go out at the same time. Maybe there's a shared X/Y counter, bus, etc. upstream?

It's been quite a few years since I've worked on an Asteroids PCB, so figured I'd drop a post here and see if anyone has ideas where I should look first.

Thanks,
DogP
 

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This thread had the same problem. No solution posted though:


I'd be inclined to suspect something in the Z circuit.

However I'll also say it now, even though it doesn't intuitively look like it from what you're seeing, and how you're analyzing it (which I think logically makes perfect sense). However I've done enough of these to have learned the lesson that just when you think it isn't the DAC's, it's always the DAC's.

(At least to the point where I'd socket and swap them both first, just to rule them out. Even if you're wrong, socketing the DAC's is never wasted effort. You're just paying it forward for the next guy.) :)
 
Ah... yeah, I was suspecting X/Y since e.g. the moving asteroids traveled "through" the dark lines (the dark lines seemed static like a monitor's shadow mask, and didn't move with anything drawn on the screen, like a missing DAC bit)... but maybe Z makes sense. I'll definitely have to check it out on the scope.

I doubt I have any new DACs in my hoard, but I believe they use the same DAC as Omega Race... and I've got plenty of those parts boards. Thanks!

DogP
 
Just be sure to give us an update!

(I should talk, as I know I've seen this one before on my bench, but I don't remember what fixed it. And I don't take notes on every board.)
 
Well, rather than doing things I should have been doing this AM... I grabbed the scope. I think I'm convinced it's X/Y, but I'll try replacing the DACs and see.

On a side note - the CH2 knob on my analog scope is broken internally, so I've got another thing to fix. :-/

DogP
 

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thinking if it has something to do with the z section I would use a scope and measure the signal output of pin 7 d10 and pin 7 a10. these are control signals for valid x and y outputs to turn the z axis on and also b8 pin 8 which combines the two then I would follow through the z output path starting with k9 and h10 of course the transistors q8 and q9 and q7 in case they have slipped out of spec.
 
Thanks for the tips guys... I'll be sure to post an update with what I find once I dig into it.

DogP
 
Finally got back to this... and yep:
Looks like bad LSBs on the X DAC...

I confirmed that there weren't any stuck bits on the digital side, so I installed a new X DAC and it looked correct again. I swapped the Y DAC as well just to make sure there wasn't anything wrong with that, and it was fine (I guess with X jumping bits, it made Y seem more "dotted" on the diagonal lines).

And I fixed the knob on my scope while I was at it. :)

Thanks,
DogP
 
This thread had the same problem. No solution posted though:


I'd be inclined to suspect something in the Z circuit.

However I'll also say it now, even though it doesn't intuitively look like it from what you're seeing, and how you're analyzing it (which I think logically makes perfect sense). However I've done enough of these to have learned the lesson that just when you think it isn't the DAC's, it's always the DAC's.

(At least to the point where I'd socket and swap them both first, just to rule them out. Even if you're wrong, socketing the DAC's is never wasted effort. You're just paying it forward for the next guy.) :)
That is one of my biggest pet peeves. Never seeing a solution. Can't tell you how many times I've searched threads and see one that comes up with what seems like the issue I have. Scrolling though it just see it drops off to nothing from the OP as to what they found if anything.
 
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