Asteroids PCB "warmup" issue

danweb

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I am having an issue with my Asteroids PCB.

When the vectors first start to appear on the screen I get very little deflection. As the game warms up the X and Y output voltage increase, and the deflection increases, and images start to "grow" and slowly become the various screen elements. This is both in the horizontal and vertical. After a minute or so the screen is complete and the game functions normally. The effect is actually pretty interesting and I have uploaded a youtube video of it:

http://www.youtube.com/watch?v=ORPk-b9K5A4&context=C3b16db4ADOEgsToPDskI8k1c2ECvCeEUgZTpVI759

I went thru the Asteroids repair encyclopedia and various logs online, but couldn't' find this exact situation. I would apprecaite any input.

Thanks,
Dan
 
Based on the description, I though it might be a monitor issue. But watching the video... that's certainly a PCB problem.

You hope it isn't the DACs... Looks to me like something in the "X AND Y POSITION COUNTERS" section of the schems (bottom right corner of sheet 2A). The details of that section kinda depend on your PCB dash-number and revision, but you might try piggybacking some of those LS374s, or the LS191 counters.
 
...As the game warms up the X and Y output voltage increase, and the deflection increases, and images start to "grow" and slowly become the various screen elements...

If the voltages are off then start to increase as the game warms up then you need to fix the power supply section first.

This must be rock solid for you to step onto other avenues of troubleshooting.

Start with that.
 
I swapped in an asteroids DLX PCB and it doesn't have any of the same issues, so its definitely on the main PCB.
 
There's a seperate 5V supply, ON the game PCB, just for the DACs. It's labeled "5VDAC" on the schems. It's generated by a 7805 regulator off of the +22V (which is in turn derived from 36VAC). Should be the only 7805 on the board. Anyhow, it supplies power to both DACs, and your problem appear to occur on both axes... so it seems worth checking early.
 
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