galaxian jitters

paul400

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stars have not been flowing smoothy, very jittery and choppy. rest of the game plays nice and smooth.checked all connections and everything seems tight and voltage is good.
 
stars have not been flowing smoothy, very jittery and choppy. rest of the game plays nice and smooth.checked all connections and everything seems tight and voltage is good.

It is probably a connection problem with a custom chip or bad custom socket. If it is like a Galaga the 54xx chip is the one that generates the star field but it could also be a weak ram chip also.
 
it test mode the stars seem fine, smooth flow. getting no ram errors either, dont know if its a custom chip, galaxian and pacman use almost identical pcb boards, unlike galaga two board set.
 
it test mode the stars seem fine, smooth flow. getting no ram errors either, dont know if its a custom chip, galaxian and pacman use almost identical pcb boards, unlike galaga two board set.

I will look at my Galaxian board today. I am just waiting on some rom chips that will be here today.

Many time the ram will test good but if it is weak or constantly running it will slowly start to fail.

You might want to check the voltages while the game is running. This is one of the stragest boards I have looked at. This board wants 7,10 and 36 volts ac.

Just check the chips for +5.
 
Galaxian doesn't have any custom chips :)

The starfield generator is a LFSR, or linear feedback shift register, which is a pseudo-random number generator comprised of two shift registers and a few gates. If you look at the schematics, it's on the upper right part. I'd start there...

-Y
 
Galaxian doesn't have any custom chips :)

The starfield generator is a LFSR, or linear feedback shift register, which is a pseudo-random number generator comprised of two shift registers and a few gates. If you look at the schematics, it's on the upper right part. I'd start there...

-Y

Yep. Also the 36vac is for my Dig Dug board which is my other project at the moment.
I just had a brain fart.

Mine had very strange mods done to it. It had pins 25 of 1h 1l cut and a jumper wire going to pin 1 of 3k I think. The rom board had 2732 chip and a different board all together.

I need a pic of the board with the two rom chips and crystal with the chip right next to it solder side and component side.

The strangest was a wire going from a pin, not sure which pin but I think it was pin 1 of a 74ls368, going to the case of the crystal. Since I cut that wire I have no clock.
 
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