[Already resolved ]Regarding a strange phenomenon that occurred with my DIMM for NAOMI

Hello to all fellow arcade board users.

My DIMM has 256MB of built-in memory and BIOS version 3.17. Yesterday, an additional 256MB stick I bought from an online shop arrived, so I installed it into memory slot 2.

However, after inserting the new memory, the NAOMI system refused to boot up entirely—there was no video output and not even a boot-up sound.

I suspected issues such as poor contact between the cartridge and motherboard, loose internal DIMM connectors, or cracked solder joints within the DIMM unit. I should mention that the NAOMI system boots up without any problems when the DIMM unit is removed.

I tried visually inspecting the solder joints, reseating the connectors, and cleaning the connectors multiple times, but nothing worked; there didn't seem to be any physical hardware failure.

After spending over six hours on this, I was ready to give up and sell the DIMM unit online.

Then, I remembered something: this strange issue had started right after I swapped the memory.

I removed the stick from slot 2 and turned the power back on. To my surprise, the system booted up successfully, and the DIMM check passed without issues.

Thinking the newly purchased memory might be defective, I swapped the memory in slot 1 with the new stick.

Surprisingly, the system booted up and passed the DIMM check perfectly; the memory appeared to be functional.

I then inserted the original memory stick into slot 2 and turned the power on again, but the system failed to boot entirely, leaving me with a black screen.

It seems my DIMM unit prevents the system from booting at all if memory sticks are inserted into both slots 1 and 2.

I couldn't find any information about this specific problem online, so I decided to share my experience here.

I plan to buy a 512MB memory module to test further, though that likely won't happen for a while. Please forgive any awkward phrasing, as I am using Google Translate.

I would appreciate it if anyone who knows how to solve this problem could reply.

Could just be dirty contacts on the formerly unpopulated Dimm slot… try reseating the ram a few times, see if that clears it…

Here's a thread dedicated to upgrading DIMM memory- it may have information relevant to you.
https://www.arcade-projects.com/threads/naomi-net-dimm-256-mb-to-512-mb-upgrade.20952/

You've already tried the troubleshooting tip I would've recommended, which is to swap the known good stick with the new one. Since that worked as well, the next step is to consider the socket. With that in mind, take some contact cleaner (like DeoxIT) and thoroughly clean the socket. Once dry, firmly (but gently) resocket the RAM stick and attempt another boot.

In the meantime, the original poster of the thread I mentioned identified that regardless of their efforts, they were unable to get both slots to work; however, they did find that upgrading the single slot to 512 MB (like you're intending to try) did work. In their case, the memory format that worked for them is quoted below:

---- Translated (please forgive any errors by the translation software.) ----

DIMMメモリのアップグレードに関するこちらのスレッドに、参考になる情報があるかもしれません。
https://www.arcade-projects.com/threads/naomi-net-dimm-256-mb-to-512-mb-upgrade.20952/

正常に動作することが確認されているメモリと新しいメモリを入れ替えるという、私がお勧めしようと思っていたトラブルシューティングは、すでにお試し済みですね。その方法で動作したということは、次はソケットの状態を疑ってみる必要があります。そこで、接点復活剤（DeoxITなど）を使ってソケットを丁寧に清掃してみてください。乾燥したら、RAMモジュールを（力を入れすぎないようにしつつ）しっかりとソケットに装着し、再度起動を試みてください。


なお、先ほどご紹介したスレッドのユーザーの一人は、あらゆる手を尽くしても両方のスロットを動作させることはできませんでしたが、片方のスロットを512MBにアップグレードすること（今回あなたが試そうとしている方法）には成功したと報告しています。そのユーザーの場合、動作したメモリの仕様は以下の通りでした。

DCrosby said:

512MB PC133 133MHZ SDRAM
168PIN HIGH DENSITY
Non-ECC Memory

Click to expand...

幸運を!

I am writing to report that this issue has finally been resolved.

To begin with, the reason the Naomi system wouldn't boot when I installed two memory modules was simply that the voltage was too low.

When I raised the voltage slightly, it booted up successfully, but an "Error 27" appeared.

It turned out that the problem wasn't dirty memory slots or a hardware failure.

It was a compatibility issue between the memory modules themselves.

I never would have suspected that was the cause until I found this site: (https://www.dentsubo.net/~nosuke/diary/diary.php?y=2026&m=2&d=26&n=26&x=26)

It stated that if memory modules from different manufacturers or with different model numbers are installed in the two slots, the system fails to recognize any of the memory.

Acting on this information, I purchased 256MB memory modules from the same manufacturer and with the same model number, and tested them today.

To my surprise, all the memory was recognized correctly, totaling 512MB.

Games like *Melty Blood: Actress Again* and *Rhythm Tengoku* also booted up without any issues.

This specific problem had not been mentioned anywhere else, including other sites or discussion threads.

That blog contains other useful information regarding arcade boards, so I highly recommend checking it out.

I hope this thread proves helpful to anyone else struggling with the same issue.

Thank you.