Space Invaders Duplicate Graphics

That would make sense if the two banks of RAM are interleaved from top to bottom where the top 4 lines of characters are rendered from bank 1 and the second 4 lines from bank 2, etc.

Bank1-A (Top of Screen)
Bank2-A
Bank1-B
Bank2-B
Bank1-C
Bank2-C
Bank1-D
Bank2-D (Bottom)

If the chip select was stuck, it would render the same bank twice.

Bank1-A (Top of Screen)
Bank1-A
Bank1-B
Bank1-B
Bank1-C
Bank1-C
Bank1-D
Bank1-D (Bottom)

They not.
Odd rows are in one bank, even in the other.

A0 drives the bank select logic:
1761403737888.png
 
to translate for @HudsonArcade he is showing you the schematic for a 2 board space invaders. you are using a 3 board taito. the control chips he is referring too are actually on the rom board aa017749 should be chip 9 for the what he has as b6.
 
Alright so to clarify on I want to check pin 17 of the ram chips on the cpu board, and chip 9 on the rom board?
 
to translate for @HudsonArcade he is showing you the schematic for a 2 board space invaders. you are using a 3 board taito. the control chips he is referring too are actually on the rom board aa017749 should be chip 9 for the what he has as b6.

To actually translate, I was demonstrating that the post I was quoting was completely full of shit and shoudn't be confusing the issue.

Without knowing of the many versions of Taito ROM boards he's got, it's useless to quote chip #s.
 
To actually translate, I was demonstrating that the post I was quoting was completely full of shit and shoudn't be confusing the issue.

Without knowing of the many versions of Taito ROM boards he's got, it's useless to quote chip #s.
My rom board is aa017749, are there more differences within that revision number?
 
he said what it was earlier. thats how I knew which chip you were refering too.

interesting board. looking at the layout it should be chips 1,2,3,4
f5 translates to chip 3 on your board. the chips maybe blacked out but a qtip with alcohol usually can clean them so that you can see a label.
believe e5 is on another board. my stash of plans get a little fragmented on this setup. do you have rom board aa017756
my rom board is aa017749

edit chip 3 on my board is a sn7442an

message #11
 
Ok I probed pin 17 on the ram chips and things have gone from bad to worse.

Pin 17 on every chip was perfectly in sync and look the same across the board.

Now though the board isn't running correctly at all.

First it added a third row of duplication to the graphics, now the video signal is either extremely glitches, doesn't display at all, or the game doesn't seem to play right.
 

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not familiar with that scope. is the voltage set to 500 mv? I can't remember exactly but the signal should be closer to 7. is your probe set wrong for your scope. the frequency doesn't look right the shape looks close but I think the frequency setting on scope is distorting. there is no way that pin 17 can be in sync on every pin 17 since they come from 2 different pins. you can't see them in sync unless you use 2 channels on scope and compare
 
After @HudsonArcade pointed out my assumptions on how the memory is laid out was incorrect, I'm not so sure that the chip selects are the original problem. You should still continue to verify they are working properly. If they are, I would suggest circling back and look at the address lines again. A dead A7 might explain the repeated graphics. I *think* that would make it repeat the first 0-32 lines twice, then 64-96 twice, then 128-160 twice, and 192-224 twice.
 
After @HudsonArcade pointed out my assumptions on how the memory is laid out was incorrect, I'm not so sure that the chip selects are the original problem. You should still continue to verify they are working properly. If they are, I would suggest circling back and look at the address lines again. A dead A7 might explain the repeated graphics. I *think* that would make it repeat the first 0-32 lines twice, then 64-96 twice, then 128-160 twice, and 192-224 twice.

Still wrong.
 
Still wrong.
Ok, I see where A7 is wrong? A4? Or do I not know how the video works? I thought in the background, RAM was shifted out serially to the display. If A4 was stuck low, when the address tries to advance from 0x1F to 0x20, it would effectively roll back to 0x00 and count up until it hit 0x1F again, then jump to 0x0040, loop twice, then jump to 0x80. If it doesn't work like that, how lost am I?
 
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