Weird centipede sprite glitch!!?!

Vectorman

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Guys,

Anyone seen this? What causes it?

Thanks,
John
 

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Looks like your tube convergence is off.

Yes, that is true. But that's not the problem I can't figure out. Look at the shape of the numbers. There are some that are shaped correctly, but some that aren't - and the problem follows the board, not the monitor.

For example, look at the ZEROs in the bottom three scores, and compare them with the ZEROs in the two above the bottom three.

Look at the difference between the first S and the last S in "SCORES"

Weird, huh?

John
 
Centipede Glitch

Thanks John for the post! This is a picture using a different monitor. Any help is greatly appreciated!
 

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I don't think it's a ROM issue. I saw this once a long while back. I believe it's a problem somewhere in the Vertical Motion Object circuit.
 
I thought the sprites ("motion objects" in Atari-speak) were the independantly movable graphics, like the centipede, the player's ship, shots fired, etc. This appears to be jacked up in the alpha-numeric graphic layer (look like there is only "playfield" other than "motion objects" in centipede).

I tend to agree that is doesn't look like a graphic ROM problem... I'd expect that to mess up the same letter in the same way each time it is displayed.

From the schematics: "The picture data ROM output D0-D7 on F7 and H/J7 are multiplexed by F8,H8, J8 and K8 and shifted out serially by H9 and J9. This serial output is latched by F9..." That's where I'd be sticking my logic probe first... (all but the ROMs F7 & H/J7)
 
I think that might be too far downstream. The outputs from the MOV circuit feed the lower address bits of the char ROMs. IIRC that's where the problem is. I almost want to say it's one of the adders H6 or F6 (since they're prone to fail) but the memory is too fuzzy.


I thought the sprites ("motion objects" in Atari-speak) were the independantly movable graphics, like the centipede, the player's ship, shots fired, etc. This appears to be jacked up in the alpha-numeric graphic layer (look like there is only "playfield" other than "motion objects" in centipede).

I tend to agree that is doesn't look like a graphic ROM problem... I'd expect that to mess up the same letter in the same way each time it is displayed.

From the schematics: "The picture data ROM output D0-D7 on F7 and H/J7 are multiplexed by F8,H8, J8 and K8 and shifted out serially by H9 and J9. This serial output is latched by F9..." That's where I'd be sticking my logic probe first... (all but the ROMs F7 & H/J7)
 
Wow, you guys know your stuff. I feel like an ignoramus. I should know this stuff - I've got an EE degree. But I just played Gameboy in all my classes and never studied, so my degree is virtually meaningless.

Thanks for the suggestions. I welcome others if anyone else knows where to look.

John
 
Wow, you guys know your stuff. I feel like an ignoramus. I should know this stuff - I've got an EE degree. But I just played Gameboy in all my classes and never studied, so my degree is virtually meaningless.

Don't feel bad-

Most of this stuff is application specific. I know that you can read schematics. Look around and there are a lot of similarities among these old games. Program RAM and ROM feeding the CPU and video RAM being loaded up and clocked out to the monitor.

As time went by, the video circuitry got more advanced over the years and I guess everything went to the PC world. To be honest, I haven't seen many schematics for stuff after the 80's.
 
So how did you actually pass for the degree then ?

I actually graduated with about a B average. How? I'm a GREAT test taker. I'm also a great crammer. I would skip class for 4 weeks, then just pull an all-nighter staring at the books and the formulas, and then go in and scrape by. Everything was graded on the curve, so sometimes I could get 50% right and still get a B because there were so many people who did even worse.

Believe me, I wish I could do it over again. I'd either skip school completely and get right to business, or pay attention and try to learn something.
 
Sorry, no it didn't. I just gave up and put in a different Centipede board.

Thanks for asking though,
John
 
Sorry, no it didn't. I just gave up and put in a different Centipede board.
Out of curiousity, would you want to sell that board? Feel free to PM me if so .. I'd be curious to take a look and see what's wrong with it (I love debugging obscure problems like this)

LeChuck
 
Out of curiousity, would you want to sell that board? Feel free to PM me if so .. I'd be curious to take a look and see what's wrong with it (I love debugging obscure problems like this)

LeChuck

Next time I have a Centipede in the shop I'll try to find it. I put it back on the shelf with 30+ other Centipede boards and now I can't remember which one it was. I normally label them but for some reason forgot with this one.

Thanks,
John
 
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