Sega Naomi help


Hey guys. I got a problem with my Sega Naomi. It isn’t giving me any picture or sound even when I plugged it in directly to a PC monitor. When I plug it into Jamma via Sega I/O, I get nothing. The dipswitches are set correctly when I plug it into the Jamma (1 up; 2,3,4 down). I know the Jamma is working fine because I plugged it into my SF2WW and it works.

I am using a ATX PSU with adapters to power on the Naomi. I check the voltage for each socket and its giving me the correct or very close to the correct voltage. I replaced the 0.1F supercap and check the continuity for the 8 pin bios chip and there is signal for every one of them.

I have 2 Naomi MoBo that actually does the same thing so it must be something in my end. Any suggestions?


PheNOM, which IO board are you using?


Sega I/O. The monitor detects the video signal but no picture.


Have you tried a different VGA cable? Make sure the dipsettings 1234 are all set to off before powering it on. Naomi also takes awhile to bootup. Not all LCD’s support naomi resolution.


I have tried 3 different VGA cables. Actually, I used a working CRT monitor that I had lying around. I do realize that it could take like 30 seconds to boot up but I left it on for 30 min and its still didn’t work.


My guess is probably the PSU you’re using…Maybe increase the voltage slightly, i know i have to do this for certain games, this might be the case.WARNING Only do it if you’re willing to risk possibly frying your board. What are your current voltage readings?


Red - 11.97v
Yellow -5.18v
Brown - 3.44v

I should add that the setup that I have currently has worked before but now it isn’t.


Those numbers seem ok a bit high on the last two…How are you connecting the VGA cable, straight to the naomi board? If so, try connecting it through your Sega I/O instead.


Yup, directly to the monitor from the Naomi. When I plug to Sega I/O to Jamma, I get the same results, detection but black screen. The only thing interesting that happen is if I the dipswitch to all off. Then it gets all white and fuzzy which it supposed to do on a 15hz monitor.


The dips should be all off for 31k, so make sure those are set before powering on the Naomi to your computer monitor. Im guessing this is your Sega i/o try connecting your computer monitor to the VGA in instead of straight from the naomi mother board.


When I connect the Jamma I am using the 15hz Monitor in the arcade cabinet that I have. When I plug the VGA directly I am using the PC monitor.

So when I use the Jamma, switches are 1-on, 234 off and when I use the PC monitor, switches are all off. I also make sure to change the switches before I turn on.

Going back the PSU, do you think voltage is affecting the Naomi from working properly?


Its a strong possibility its the voltage because when it comes to other games like CPS2 or Atomiswave, you have to have certain amount for it to work or wont power properly. Try to adjust it to 12v, 5.1v, & 3.3v as close as possible. I cant think of anything else since you say the I/O works when using jamma…Maybe the filter board might need to be replace. I hear these are faulty quite often but i haven’t experienced it. You should try posing at or neo-geo tech forum or maybe even Very knowledgeable people there when it comes to arcade stuff.


Thanks for you help. I have posted on those forum the same time as this thread was created but with no response.