Galaga Graphics Issue

jhend

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Feb 21, 2012
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Georgia
For whatever reason, the sprites on my Galaga are all pink squares. Some of the sprite data shows up inside the pink squares and some of it is just completely missing (just pink squares only). Some of the characters are missing and are replaced by a giant white horizontal bar through the screen. I've cleaned the 02xx custom chip twice and replaced the socket, along with replacing the crappy resistor packs. I verified that the EPROMs are good and I've also replaced the 74ls245 at 2K and the 74ls377 at 2M with no luck. I have been probing with my oscilloscope and found that the line labeled as "obj" in the manual is stuck low. It comes from pin 2 of 2M Not sure if that's normal or if it's not working correctly. Any suggestions?

Thanks
 
Do you have any activities @Pin3 (DB5A) of 2M?
If no, check RAM @1K.
What about the PROM @2N?
Also check the LS157 @5A.
 
I'll check that when I get home later. I might actually be swapping the board with a working one for free. I'll be sure to post back what I find. Thanks for the input.
 
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