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 Converting an irem m72 arcade pcb

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Drakon
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PostSubject: Converting an irem m72 arcade pcb   Fri Aug 09, 2013 12:41 pm

Okay I own a rare irem m72 dragon breed arcade pcb.  I've long since beaten dragon breed and as far as I'm concerned the game is just a quarter sucking machine which doesn't hold much replay value (but nice artwork).  Now that I have some hardware reprogramming experience under my belt I decided to look into just how hard it is to reprogram this arcade board with a different m72 game.  I decided the game I want to turn this board into is air duel.

The Irem m72 pcb has 3 layers.  Most of the rom chips for this board are on the top layer, then there's the middle layer with the jamma connector, and for some strange reason there's another row of rom chips on the bottom layer.

The Irem m72 pcb uses toshiba maskroms which aren't eprom pinout, here's the pinout comparison:



Now what caught my interest is that my particular pcb as well as many other m72 pcb pictures on the internet show the board using a mix of eproms and maskroms.  Upon inspection my board has a bunch of jumpers on it which lead me to believe these jumpers allow me to select between using eproms and maskroms.  I also found this m72 conversion guide:

http://www.paulswan.me/arcade/m82-m72.htm

In this guide the author explains how to change jumpers on the bottom layer to switch the chips from "MASK" (maskrom) to " EP " (eprom).  If you can use eproms on the bottom layer by changing jumpers and the top layer is already a mix of eproms and maskroms with a bunch of jumpers, there was a good chance I could change the top slots to use eproms as well.  To first test the socket I left the jumpers alone, burned a 27c010 eprom and installed it into a maskrom spot rewiring the eprom for the maskrom pinout, and it worked great!

Unfortunately I found one jumper that seems to control an entire row of chips, so I had to burn myself four 27c010s to replace the four maskroms on the top board.  Here's the picture of the rom area on the top board with jumpers circled, in this picture the jumpers are what I believe to be all set to eprom.  I added some extra decals to the jumper I changed to switch the row of slots from maskrom to eprom mode.



I numbered the maskroms and removed them:



Burned four 27c010s with the maskrom dumps and inserted them into the pcb with the jumper set to what I believe is eprom.  I had to guess with the jumper setting since there's no jumper information out there for the m72.  Fired the board up and.....





Win!

Some m72 games need me to reprogram a security chip too, luckily air duel doesn't seem to be one of those as the mame dump has no security chip file.  The only way to know for sure will be to burn the entire game which is on hold until more 27c010 chips arrive.  This board will need something around 20 27c010 chips to convert.  Now that I have the top board running completely off of standard off the shelf eproms I'm one step closer to having a convertible m72 pcb.
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Grambo

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PostSubject: Re: Converting an irem m72 arcade pcb   Fri Aug 09, 2013 1:09 pm

That's amazing. How convenient is it that they're just simple jumpers?
Stupid maskroms, lol.
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PostSubject: Re: Converting an irem m72 arcade pcb   Fri Aug 09, 2013 1:28 pm

Grambo wrote:
That's amazing. How convenient is it that they're just simple jumpers?
Stupid maskroms, lol.
Very convenient.  It would have been better if they used eproms I could have just reprogrammed the whole board, instead of ordering 30$ or so worth of eproms, oh well.  My gameboy devcart works the same way I wired in a switch to select between eproms and flash chips for address line differences.

Regarding inconveniences I learned about this board, r-type uses a special type of rom board which is different from all other m72 games.  Judging the difficulty of this conversion guide for turning one of these non r-type boards into a r-type:

http://www.paulswan.me/arcade/m82-m72.htm

R-type seems to not be compatible with the common style rom board.  Luckily I think the pc engine cd version of r-type is superior to the arcade version so I'm good with that game.

Other invonveniences is the custom mcu (I think that's what it is).  Certain games need me to reprogram some intel 8751 mcu chip on the board.  I need to read up on this chip.  To reprogram it I would have needed to buy a 15$ adapter for my willem and fiddle around getting that to work.  I've read a few people finding m72 boards converted into air duel and the mame dump of air duel is maskroms only so I'm hoping that will go smoothly with just 17 burned eproms and some jumper changes.  I'm very lucky that air duel is the m72 game I found most fun in mame, other m72 games looked more complicated when I looked at the romsets.  I'm hoping this will work with just a straight rom swap but there's only one way to know for sure.
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PostSubject: Re: Converting an irem m72 arcade pcb   Fri Aug 09, 2013 5:08 pm

Good luck with all that. Sounds like a bit of a task.

I've never played any of the M72 games before... they look pretty fun on YouTube though.
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PostSubject: Re: Converting an irem m72 arcade pcb   Fri Aug 09, 2013 8:26 pm

I discovered that my street fighter 2 world warrior pcb has a small army of 27c010 chips on it.  I burned the romset of air duel but it wouldn't start on this board.  After a google search is seems that the air duel security chip hasn't been dumped and the game won't run without that grr.  Since I can't convert this board into another game until the adapter comes for me to reprogram the security chip I decided to convert the rest of the board to run on eproms.  I burned the dragon breed mame romset, played with jumpers, and it works great!

Now I have the entire board 100% running off of standard off the shelf eproms.
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