Board repair experts: What failed component causes sprite color shearing?

ifkz

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Board repair experts: What failed component causes sprite color shearing?

I have a couple of otherwise playable boards that have and odd color faults from 1986 on up. Basically the colors keep shifting and are shearing on sprites. The shearing and color changes are not static, they change as long as the object is on screen. I'll see if I can get a good picture of it:
sh.jpg


I've circled two sprites with problems. The pointer shows a little of the shear.
 
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"Palette rams?" Can some one give me some good examples of this type of chip? I've found one example, a 6116 "skinny dip." Another example, "2018 that is compatible with a 6116 (from another repair log)." Pictures would be nice too.

Once I know what chips to look for, what is the best way to track this down. Start piggy backing chips?

How do I know what common ram sizes are compatable by manufacturer number? Is there a chart of types and manufacturer codes somewhere for the novice board repair tech?
 
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Could be RAM, ROM or TTL I'm afraid.

As for what chip is what? SRAM is SRAM is SRAM there is no specific type for pallete ram. 2018/6116 are used as system RAM, sprite RAM, sound CPU RAM, background RAM and pallette RAM, as are practically any chips going.
 
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I tried some piggy back tests with identical RAM I had around, no changes for better or worse. Looks like my boards have TTL problems, I am likely in scope territory; at least they are still playable as is. I guess I will either (1)find an inexpensive board repair person or (2)learn enough to fix them on my own. So far I have slightly faulty Splatterhouse, Wonderboy, Aero Fighters, and Rolling Thunder (not playable) PCBs. Not exactly easy boards to replace.

Any reference point to the sizes and common manufacturing codes for types of RAM used on arcade boards? Or will I be thumbing through datasheets for each ram chip I find?

I have noticed RAM is usually in the slim rectangular package, but some look to be the size of EPROMS. Is this larger ram just in a different "package," or does it have another function I'm missing?
 
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You may want to go with actual socket replacement (add a socket and replace) instead of piggybacking. When I had a sprite issue on a DK, I tried piggybacking, but it didn't help much (if at all). When I replaced the chip completely, the issues went away.

Might not be the fix in your case...
 
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