Centipede - Very Wrong Colors. Not monitor.

dabone

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I'm helping a guy out with his centipede, and he's not a technical person, and first off, he tried to replace his big blue.
The first time I saw the game, this is how big blue was wired.

bigblue.jpg

After sorting that out, (and finding the correct screws for the replacement cap....)
The board came up with 10 beeps, so I replaced the ram at n5, and that brought the machine back to life.

But.. the colors were wrong...

Now the original reason I was called upon to help is that his monitor had died, and he took it to a local guy, that hooked it back up, it ran for a day, then smoked and died.... (k4900 I'm trying to find a chassis for)
I took a extra g07 I had on the shelf, but hadn't tested in years over to the location, and put it in and noticed to colors were bad, so I thought the monitor was bad and I forgot to label it.
So I grabbed my old faithful K4600 out of my Multiwilliams (It looks fine, colors are great), and took it over tonight, and same bad colors.

Here's the attract screen.

Attractmode.jpg

And here's the colors when I'm cycling the colors in test mode.

testscreens.jpg



Any suggestions?
The game seems to play fine, the sprites are there, collision detect is working fine.
Also the wiring harness seems to be unmolested.

(Also, anyone have a link to the schematics???)
 
Thanks... after much digging, I verified the russian chips I have in my sram drawer are 82s25 clones, and I've ordered the other chips in the circuit from mouser along with my other real work parts I needed to finish ordering tonight.
 
You should order a logic probe if you don't have one, and do some poking around fist, before shotgunning a bunch of chips.

You're more likely to cause new problems just replacing stuff, which makes finding the original problem even harder.

The Elenco LP-560 is a good cheap one most of us have. It'll run you about $25 on Amazon.
 
I've got a probe and a scope, I'm just grabbing all I may need before I go down there again. I don't have a way to test it at home, so I'm planning on just one more trip over there.

My money is on the color ram....
 
Gotcha.

Yes, that's one possibility. But it's worth probing around the color section. You might get lucky and find something dead or stuck.
 
Gotcha.

Yes, that's one possibility. But it's worth probing around the color section. You might get lucky and find something dead or stuck.
Mark's going to probably come in and flex how large his brain is when I don't even fix Centipede boards, but how is the color generation performed on these?
 
You should order a logic probe if you don't have one, and do some poking around fist, before shotgunning a bunch of chips.

You're more likely to cause new problems just replacing stuff, which makes finding the original problem even harder.

The Elenco LP-560 is a good cheap one most of us have. It'll run you about $25 on Amazon.
Btw... for a laugh... I've had this in my tool bag for years... It's helped with fixing a few arcades, and lots of Commodore pets, vic and 64s... along with other stuff.
 

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(Probably should not respond from a plane…)
There is a color PROM on Centipede. I've had that and the color ram cause the issues. I looked though my repair logs and had a color ram failure with that exact same color screen
 
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(Probably should not respond from a plane…)
There is a color PROM on Centipede. I've had that and the color ram cause the issues. I looked though my repair logs and had a color ram failure with that exact same color screen

There is *no* color PROM on Centipede... only the RAM.

You're getting all 4 color combinations in the background, so AREA1/0 aren't the problem.

It's likely that the high data bit coming off the 82s25 is bad, so you're getting the "modified" colors through the weak pulldown paths, but it could be a bad '175 or '07 giving the same effect as the ram output being stuck high.
 
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There is *no* color PROM on Centipede... only the RAM.

You're getting all 4 color combinations in the background, so AREA1/0 aren't the problem.

It's likely that the high data bit coming on the the 82s25 is bad, so you're getting the "modified" colors through the weak pulldown paths, but it could be a bad '175 or '07 giving the same effect as the ram output being stuck high.
Right. New rule. Don't post from memory on a plane 🤦‍♂️
 
It's likely that the high data bit coming off the 82s25 is bad, so you're getting the "modified" colors through the weak pulldown paths, but it could be a bad '175 or '07 giving the same effect as the ram output being stuck high.

Actually check that...

You're not getting black at all, so I'd suspect the '175 or the '07 before the RAM.
 
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