Using 2x 27C322 Eproms to replace a bad 64mbit prom? (C rom)

bytestorm

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Is it possible to replace a 64mbit toshiba prom with 2x 27C322 eproms? Do they even have the same pinout? (TC5364205AP)

I saw a post somewhere about combining 2x 27C322 to replace a broken/bad 64mbit toshiba prom in a mvs cart.

How to connect them 2 eproms to get them to act like a 64mbit prom? Just piggyback and lift some pins pins?

I found this picture, from another forumpost.

"If the PCB decodes the ROM with /CE, attach your decode circuit to /CE, if it uses /OE attach circuit to /OE."

decoder.png

Could anyone shed some light on this please?

I have a RBFF2 that gives me constant jailbars :(
 

bustedstr8

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I have never tried, but can you even close a cart with a piggybacked chip?
 
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jesesfbi

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I have never tried, but can even close a cart with a piggybacked chip?

You can, you put one on topside and another on the solder side. If you look at a strikers bootleg you will see stacked m27c322 lol.
 

HMG

H = Heinously, M = Massive, G = Gonad,
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An easier option would be to get a 64Mbit flash chip on a 42 pin adapter.
 

bytestorm

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You can, you put one on topside and another on the solder side. If you look at a strikers bootleg you will see stacked m27c322 lol.

Allright, nice to hear that there could be a solution in case of a broken prom. Was afraid these big ones were not replaceable.
Going to heck the solder joints at work today and see if there could be a microscopic crack somewhere hopefully :/

Thanks for the tip!
 

HMG

H = Heinously, M = Massive, G = Gonad,
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You could also just reflow any suspect chips before you get hasty and replace a chip.
 

Xian Xi

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Is it possible to replace a 64mbit toshiba prom with 2x 27C322 eproms? Do they even have the same pinout? (TC5364205AP)

I saw a post somewhere about combining 2x 27C322 to replace a broken/bad 64mbit toshiba prom in a mvs cart.

How to connect them 2 eproms to get them to act like a 64mbit prom? Just piggyback and lift some pins pins?

I found this picture, from another forumpost.

"If the PCB decodes the ROM with /CE, attach your decode circuit to /CE, if it uses /OE attach circuit to /OE."

View attachment 11768

Could anyone shed some light on this please?

I have a RBFF2 that gives me constant jailbars :(

What kind of Jailbars? It might not even be the C roms and instead the S rom or just a connection.
 

bytestorm

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What kind of Jailbars? It might not even be the C roms and instead the S rom or just a connection.

The jailbars is on top of everything, like 5mm wide vertical, covering all the screen, with even spacing.
Tried to clean the contacts but still there :(
 

Xian Xi

JammaNationX,
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The jailbars is on top of everything, like 5mm wide vertical, covering all the screen, with even spacing.
Tried to clean the contacts but still there :(

If it affects the fix layer then it isn't the C roms. Can you post a picture?
 

bytestorm

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Oh this is wierd. When I get home from work the game is perfectly fine!? I haven't done anything except taking it apart and checking under a microscope.. I did push the Roms I think but nothing is resoldered or anything, it just works! Argh :(..
Maybe I should start the game without the cart shell, and push the Roms a bit when the game is running?
To see if I can get the bars back? :/ I don't want them back but I have a feeling that they can be back anytime is I don't find the source :(.
 

bytestorm

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Could be a cracked solder joint or lifted leg on a flat chip.

Yeah, that's what I'm thinking.. And it's not that many chips so it's probably better to try and find it.. Even thou it's working now.. Thanks for the tips everyone! Hopefully I can reproduce the problem and reflow the solderjoints.

The bars was in top of all graphics, any suggestion wich chip could cause that? Wich chip holds tha front most data, or controls it?
 

smkdan

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We have a guide on the wiki with glitch images for reference:

https://wiki.neogeodev.org/index.php?title=Graphic_glitches

If the bars were on top of everything with all odd/even pixels affected then it sounds like S ROM data (bottom of that page). If that's the issue, then the S1 ROM on the cart has pins D0~D7 leading straight to the cart edge so it should be simple to check.

The bars was in top of all graphics, any suggestion wich chip could cause that? Wich chip holds tha front most data, or controls it?

All non-transparent graphics from the S1 ROM (FIX layer) has priority over all sprites. Most status bar content comes from the S1 ROM so if that's affected by the glitches too, then it's definitely an S1 issue as the C ROM data (sprites) always has lower priority and can't affect it. A photo would help confirm it for sure though but that's the general rule.
 
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