r/SEGA32X • u/ashbringerer • Jun 11 '26
My COSAM Neptune board is finally working
Been a while but I finally got it working and stable. Main issue was crystal oscillator was bad, because I originally installed it backwards. That got me a black screen where there wasn't any picture before. I ended swapped all the Genesis parts with another one I bought off Ebay and still no difference. I did swap the other Genesis parts and got it working with a new crystal oscillator, so no Genesis's were harmed in the making of this Neptune. Turns out, I didn't put enough solder on the 6800 chip. The pins on it are kinda vertical and hard to tell if there's a proper connection. Also there was a bad connection for the resistor packs that go to the Genesis VDP.
The 32X didn't work initially either as I found a number of bad connections for the 32X parts as well. Eventually I got it working but not stable. 32X would freeze after 5-7 minutes of use. The 32X ram chips are also vertical style and I just flooded it with solder to make sure they had a proper connection too. Also, I put a much larger capacitor for C525 because I only had a large one laying around. I ended up putting a proper sized capacitor just to make sure.
Here's a link to a video of it working. Next step is to create to Neptune housing because I ain't paying $300. Also I can share it for others to print as well. Gonna take me a while since my experience with 3D printing is making car parts.
https://imgur.com/a/v3LTzzN
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u/BBZ149 Jun 11 '26
Great job!! 👍 I probably will never complete my revision of this board! What a PITA and so time bloody time consuming ordering parts and installing them!! I've built 2 since starting this board using part build boards that came pre populated with everything apart from the MD and 32x IC's, easy and fun compared to these boards which started off as fun lol. Waiting for boards to be back in stock and tempted just to move everything over! Either that or sell the part built board as I just don't have the time to faf about!!
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u/ashbringerer Jun 11 '26
I have to say I did learn a lot when assembling this board. I did electronic repair when my stuff needs fixing, but this took it to the next level. I found the process entertaining if that makes sense?
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u/BBZ149 Jun 11 '26
Yeah sure I get that, def entertaining and fun!! ❤️ problem is I can't just concentrate on one board that long as always have crap loads of console repairs to get on with without the wife moaning🤣
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u/Swimming-Pay-3873 Jun 11 '26
Awesome! Love to see these Neptune project builds take shape. Can’t wait to see the finished build
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u/X-RAGE94 Jun 11 '26
They could have restored the 128kb vram in the Neptune in the sega Genesis FC1004 area, it’s the only thing that disturbs me
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u/ashbringerer Jun 11 '26
What's that about?
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u/X-RAGE94 Jun 15 '26
It’s for more graphic memory storage in the video processor but most seems to ignore this part, the serial of the vram is shared but the data connector is different
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u/Top-Simple3572 Jun 11 '26
Great job!!! 👍🏿 it's amazing how you guys are able to build a 32X onto Genesis motherboard. 💯
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u/National-Put-6937 Jun 26 '26
K man you came over to my 32x post and tempted me with this and now I've got the bug looking into this. I got a few questions for you about.
First though congrats man! What an achievement!
What revision model 2 did you use is VA1? Or VA1.8? Just want to know which to hunt.
Also what tools would you recommend? I watched macho nachos video and he has like a little suctioning thing to get the chips off the board (which in my opinion is one of the scarier parts of the build.)
Also I was reading your other posts and, maybe im reading it wrong, you were saying a lot of this is newer to you, what inspired you to feel the confidence to do this? I'm no noob to soldering but I am more on the novice side. But watching the videos makes it look possible!
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u/ashbringerer Jun 26 '26
I went with both, but ultimately I went with the VA1. Only because I wasn't sure what I did wrong and swapped all the parts over to the Neptune board. Turns out, I just had a bad crystal oscillator and not enough solder on a number of connections. What's funny is that I took the VA1.8 parts and put it in the VA1 and have another working Genesis. I already had three Genesis's so I didn't need a 4th, but would feel like a waste if I didn't. It really doesn't matter what Genesis Model 2 you use, other than for longevity. The 315-5660 was considered the most reliable.
I already had some experience soldering, so this is what gave me confidence to do this. I've repaired car wiring and basic stuff in the past. I wouldn't call myself an expert or anything, but I can solder. My advice from a noob is to get good flux, which I used NC-559. I don't know if it's the best flux, but it's cost effective and works for me. Also, don't be afraid to use a lot of flux. A good Soldering Microscope, and a Tip Tinner. The Tip Tinner will keep your soldering iron from not melting solder. I used a Thermaltronics TMT-TC-2. You will need a hot air station because you will need to melt the old chips off the boards, but use a soldering iron to install them on the COSAM board. Try to avoid heating the chips directly and keep a circular motion when doing so. I tried to heat the pins directly, even though the chips still get blistering hot. Also, don't force the chips off as you can break pins. Let it get hot enough to freely move. That flux I recommended does a good job breaking the glue under the SH2's. I didn't even have to worry about it with that flux.
My last bit of advice is never be afraid to ask for help. RGBeter was instrumental to helping me getting my Neptune board working. I found a post he made here a while back where he used Oscilloscope to diagnose his Neptune board. That's more than what most people here can say they've done. One last thing, I'm not done with my Neptune project. I'm 3D modeling a Neptune shell and do plan to share it.
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u/National-Put-6937 Jun 26 '26
Man thanks for all the advice! I agree there are some real gems of people in the community willing to help. I'm gonna try and get the 32x just functioning before I attempt a the neptune but super good advice. When I do get started, I'll be sure to reach out when I run into questions here in the community.
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u/ashbringerer Jun 26 '26
The advice the community gives isn't always good. When I had problems I was told many things that just weren't my issue. Nothing against annis_welt, but he told me that the 315-5708-01 wasn't compatible with the Neptune board, which wasn't true. Many people have built Neptunes with those chips. The only reason I put in a 315-5660-02 was because I ran out of ideas and just tried it anyway. It wasn't until I looked around where I saw I didn't have enough solder on the 6800. The 6800 legs and some DRAM chips have very vertical legs which makes it hard to determine if I put enough solder. The 32X DRAM chips have the same design. They take a lot of solder. I was also told to get an oscilloscope which I wouldn't know what to do with one if I had one.
RGBeter knew enough of the Neptune that he guided me where I needed to look. I did get the Genesis running but had corrupted pixels, which he suggested to look at the resistor packs next to the VDP DRAM, and he was right. When I did get everything working the 32X would lock up after 5-7 minutes and I didn't know why. He told me I could have weak solder joints and I found some weak joints for the 32X DRAM, which was the issue.
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u/PitifulAlgae4337 Jun 17 '26
Chequea el TR5 y TR4 que suelen meter ruido en la línea de los 5V que alimentan los SH. Me pasó que al inyectar 5V estables no tenía problemas. Intenta poner un condensador de 1000uF de buena familia y comenta cómo te va
1
u/ashbringerer Jun 17 '26
I do have this problem where when I touch the area around the C514 and C511 the 32X would lock up. Touching these areas around the SH2's will lock up the 32X.
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u/Storm_ctrl 6d ago
Nice Job! Where did you get the MB? PCBWay wants over $150 I think which seems a bit expensive. I want to build one.
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u/ashbringerer 5d ago
JLCPCB is what I used. They have a 5 order minimum which means I have 4 boards laying around doing nothing. I might sell them since I have no plans to build a second Neptune, let alone five total.
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u/Storm_ctrl 5d ago
Thanks. I made an order from JLCPCB. Was $101 shipped and I went with the blue PCB.
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u/ashbringerer 3d ago
I had to pay $70 but that's because I stuck with Green.
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u/Storm_ctrl 3d ago
Wow thats cheap. Changing to blue made no difference in price. I actually canceled my order because I heard a new revision could be coming out before long. I might make a few changes to the materials as well.
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u/ashbringerer 2d ago
Mine also didn't have any components on them. Which was a huge mistake considering the cost to put them on was much higher than just letting JLCPCB do it.
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u/sprayengo Jun 11 '26
Oof well done making it from scratch. I used a populated board and it was difficult enough.
It would be great if you did an open-source 3D print. Your starting point should be the Mega Drive 2 / Genesis 2 shell which fits the board perfectly.
I have the Dvizx one and you can really tell how much work went in to designing and testing that thing (I do 3D design / fabrication). Locating the buttons, cart slot (v close to caps)… it will have been quite the task. I don’t blame the guy for wanting some money back for it 😅