Gallag/Galaga game speed and freezups

HHaase

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This is an intermittent problem. Sometimes I can play for hours with everything running just fine. Then, sometimes, all the enemies will suddenly get much much faster. Other times, they just stop moving totally. Bullets, mine and theirs, follow suit..... I.E. when THEY get fast, the bombs/bullets get fast. When they stop, the bombs/bullets stop moving.

However, the player ship speed stays normal in both cases, as does the starfield backdrop. Meaning that when the enemies stop, I can still move my ship back and forth and the starfield still moves. If I don't have 2 shots in the air at the time, I can still fire (with sound) until there are two shots visible...... but then they would just appear where my ship is but never move upward at all. I can reset the game using either the slam switch or the test switch, and it goes back to operating normally.

So, my assumption is that there's something wrong in whatever sets the pace of the game speed but not that of the processor speed.... so for now I'm going to rule out the system clock. I suspect that one of the Z-80's is likely the problem, as the graphic images are unaffected, neither is the sound, nor the control inputs. I could just replace all 4, and IF that's the problem I'd be done with it, but I'd rather know a bit more about what actually controls the speed of the enemies, as if my guess is wrong I'll have to start tracing the problem in further detail.

As a side note: Anybody that can explain to me if there's any pattern to the chip locations on the board. I have the schematic, but how can I determine which chip is 4E or 10P or 8M if there's no markings on the board?

-Hans
 
It's a Gallag board, not a galaga, it doesn't have any of the custom chips on it.

My fault, I wasn't clear enough in the post itself when describing what I have.

-Hans
 
Does it do this randomly or does it do it after it heats up?

If it's after it heats up then use component cooler to help isolate where the issue is.
 
No, it's pretty much random and doesn't seem heat related that I can tell. Sometimes within 30 seconds of powering up and starting, other times it can go hours with no issue. And if I reset it, then play again right away, it also goes away for a while.


-Hans
 
I did find the +5v to be way out of whack today..... I honestly don't remember if I had checked it before. It was 5.8v at the power supply, and 5.5v at the filter cap. I adjusted it down to 5.02v at the filter, not a very fine adjustment screw it was as close as I could get.
I also finally got around to replacing the power cord for the machine,as the old one was missing the ground prong.

Seems more stable now, hasn't locked up yet anyway.

-Hans
 
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