Sega System 16b Decryption and Conversion

sabrewulf69

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I have a Tetris (5358) System 16b board with a suicided FD1094. I was looking into the process of replacing the FD1094 with a 10mghz 68000 and doing the necessary steps to convert it to an unencrypted Alien Syndrome, and I wanted others opinions on the process to make sure I understand it correctly.

From what I gather looking at the following 2 sites....


&


replacing the FD1094 with a 10mghz 68000
only additionally requires replacing the encrypted roms with unencrypted (unprotected) roms, so in my case of converting to alien syndrome, I need a full set of 256kbit 27C256 and 512kbit 27C512 eproms and then move the jumpers and install the eproms in the correct positions as in this photo of a alien syndrome 5358 board...

1000024579.jpg

One thing I don't understand however is this part of the converting process from arcade-projects...

"The main program ROMs (A5 and A7) have to be non JEDEC 1mbit EPROMs (unless the game uses a 512kbit EPROM) - 27C1000 or 27C301 are the type you will require. The other ROMs are all JEDEC type"



Any additional input would be greatly appreciated!
 
One thing I don't understand however is this part of the converting process from arcade-projects...

"The main program ROMs (A5 and A7) have to be non JEDEC 1mbit EPROMs (unless the game uses a 512kbit EPROM) - 27C1000 or 27C301 are the type you will require. The other ROMs are all JEDEC type"

27c010 has /CE and /OE at pins 22 and 24, and A16 at pin 2 (JEDEC standard pinout)

27c1000 has /OE and A16 swapped.

There are 28-pin masked ROMs with a single enable, with A16 at pin 22 (24 on a 32-pin) and VCC at pin 28 (30), that would drop in in place of a 27c1000.
 
27c010 has /CE and /OE at pins 22 and 24, and A16 at pin 2 (JEDEC standard pinout)

27c1000 has /OE and A16 swapped.

There are 28-pin masked ROMs with a single enable, with A16 at pin 22 (24 on a 32-pin) and VCC at pin 28 (30), that would drop in in place of a 27c1000.

Do you know what those roms would be? And how would that 32-pin 27c1000 they suggested even work in a 28 pin socket? Vcc would be on the NC pin and Vpp on A15?
 
Not really sure why they're talking about 1Mb roms... the alien syndrome MAME set appears to be all 27256 and 27512.

That ROM board only has 28 pin sockets, so 1Mb EPROMs won't fit.
 
Not really sure why they're talking about 1Mb roms... the alien syndrome MAME set appears to be all 27256 and 27512.

That ROM board only has 28 pin sockets, so 1Mb EPROMs won't fit.
That's why I was confused, I also found this here on klov. @caius mentioned it.


"They are used to replace 28pin non-JEDEC 1Mbit MASK ROMs
You can find 27C301 ( or most of times 27C1000) on few boards like Sega System16 or Namco System 1 but, as said, most of times MASK ROMs are used instead."
 
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