Galaxian Video Problem

prc69

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Oldenburg, Niedersachsen, Germany
Hi everyone!

I have a problem with my original Namco Galaxian board. It was modded with the four play roms and worked fine when I got it. But after two hours the video output was strange. I saw only the starfield ... no missle, no shells, no letters and numbers ... just the starfield and the stars are kind of flickering.

When I turn it off and on again I see the menu of the four play mod for the blink of an eye but then again nothing. The game plays fine (as far as I can tell). It coins, the sounds are all good.

I studied the shematics and checked the color prom which was dead on the inputs. The 74LS273 also dead on the inputs. I saw the 74LS174 on position 1U is missing ... I tried to put one in but that doesn't change anything.

I suspect some kind of timing problem. If only the color Prom was the problem I should see the missle and shells, right? Does somebody have a clue what could be wrong on this one?

cheers, prc
 
Last edited:
Yeah, I checked the logs and the troubleshooting guide already ;) There is an entry for "stars only" ... I changed the ic on that position but that didn't help, because the signals are not reaching that point. There must be something happening before. On my way back in the schematics I stumbled over the missing ls174 on position U1 as I mentioned in my first post.
But adding that one didn't change anything ...

The flickering stars make me think of some timing issue ... I will provide further data tonight when I slapped it on the bench once more ;)

cheers, prc
 
Are the stars OK? Are they moving down the screen at the normal pace or are they fast? Are they moving UP instead of down?

Does the game play blind?

If stars are OK then according to the troubleshooting guide check:
74LS86 at 6B
74LS139 at 4D

RJ
 
Yes, the game plays blind. All sounds and stuff are good. I think the stars move in the right direction. I will check the parts you mentioned tomorrow! Thanks for the tips ;)

cheers, prc
 
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