Sega Naomi Maintenance: GD-Rom Swaps (Error 24) and Arcademodbios

Naomi Error 24/GD-Rom Swaps

So a couple days ago I got a new Naomi game in the mail, popped it in and was greeted with a nice Error 24 (GD-ROM NOT FOUND). I figured something wasn't hooked up properly so I reseated all of the connections from the psu to the GD-Rom, as well as the SCSI cable going from the GD-Rom. Nothing worked? I reseated the Dimm board as well as cleaned the disc and laser lens. Error still persisted. I read online that this error is either the lid on the drive is not closed properly (which wasn't the case), the disc wasn't present, or the drive died. I was kind of mad now that I would have to spend another $75-$150 on a "new" Naomi GD-Rom drive.

Of course me being as I am and not giving up on anything until every repair option had been exhausted I did some research. I learned that the laser assembly from a Dreamcast could be swaped into the Naomi GD-Rom unit and it would usually work. So I threw both of them on the table and proceeded to take them apart. I removed the GD-Rom drive assembly from the Naomi unit, and repeated the process on the Dreamcast. I heard there are two different drives used in a Dreamcast, Mine was a Revision 1 so the drive was 100% the same as the Naomi Unit. The ribbon cable in the Naomi unit must be reused as the Dreamcast's ribbon is much to short. The power cables (2 small connectors) make the trip with the gd-rom assembly as they are the same on both systems. The hardest part was getting the ribbon cable from the Naomi into the Dreamcast's laser assembly. A trick that I figured out was to undo the screw holding the metal rail in place that the assembly glides on. You pull the rail out, slide the laser assembly off of it making it much easier to get that ribbon cable inserted into it. Once done I placed the assembly back on track (ensuring the small spring that was under the rail was put back in place), and reinstall the rail and screw.

I was figuring it had almost no chance of working as I do not consider myself an expert by any means. So I went back to my Naomi setup and hooked up the drive. Turned it on and sure enough, no Error 24. The system went right into checking memory, and started loading from the GD-Rom drive. In a minute or two I was seeing Lupin III The Typing on the screen again (figured I would use that game as I knew it worked). Just incase you were wondering, when the error would happen it would quickly say Naomi GD-Rom System and then go right to Error 24 without checking memory. So now, all I have to do is replace a $10-$30 Dreamcast, which is much more common then a Naomi GD-Rom unit. So if you ever have this problem, grab a Dreamcast and fix it yourself.

Naomi Arcade Mod Bios

Other then this problem, Which had just happened a couple days ago, I had another "problem" with Naomi. Some games that I own (such as: Virtua Fighter 4 Evolution Ver B, Guilty Gear XX # Reload, Melty Bloody Act Cadenza Rev A) needed to be run on Japanese Bios and some games (Such as the Initial D Games, since they are the English exports) Need to be run on USA bios. Also some games will change a bit depending on what Bios is installed (example Gunspike (Japan) becomes Cannon Spike (USA) and Moero! Justice Gakuen (Japan) becomes Project Justice (USA)). Plus most of the games that are compatible with the Dreamcast controller ports need Japanese bios. My solution I had in place was to buy a Japanese bios chip and swap them when needed. Only problem here is every time I pulled out one of these chips I bent the pins a little and had a feeling that after a while one of them would break or I would do damage to the Naomi 2 board in a botched attempt to remove the bios chip.

Enter ArcadeModBios. This is a bios chip for the Naomi or Naomi 2 which allows you to switch regions with a combination of dip switches 3 and 4 (which are unused otherwise). I had heard about this because someone on KLOV forums was selling a Naomi unit which hard these bios and briefly mentioned how it worked. I of course had no interest in getting his Naomi 1 unit but quickly found out that there was a version for Naomi 2 as well. The cost was about $30 for the chip shipped. Took a good month and a half to get here because unfortunately the first one he had sent got lost in the mail, but you know, those things happen. Finally got the bios chip on this past Saturday and all is well. I can easily switch from Japan Mode (3 and 4 off) to USA Mode (3 on 4 off) with just the flip of a switch without needing to completely disconnect the Naomi system or rip the bios chip out every time. So I highly recommend if you have a Naomi or Naomi 2 system at home and have games that require different bios, get yourself a Naomi Mod Bios chip.

Arcade Mod Bios dip switch settings (I received version 1.15)


Update: Many days later for the heck of it I plugged in the Dreamcast which now had the "bad" Naomi GD-Rom drive installed in it and to my surprise it works without problem. I tried about 5 Dreamcast games and all load and play without problem. I also tried Bleemcast Tekken 3 disc and even that worked without a problem. I can honestly say I can not understand why it works, perhaps there is something wrong with the GD-Rom drive that makes it not work in Naomi but does not prevent it from working on a Dreamcast console. Go Figure.