RGBeter

@leo__oliveira @krikzz To my knowledge, no available program tests Word RAM DMA to VRAM. It's more a mega drive test on the main CPU side. I have a few units where all the hardware is good, but FMVs and the spinning logos in the BIOS screen break because of this issue and no test can catch it.

@RGBeter32X @krikzz I think I already commented with you at Discord that testing only from MD side is very limited for testing the CD and recommended you Fabio's testing tool which tests using the CD CPU. The only thing that tests more things is the tool Krikzz made to research CD for MD ED PRO...

Although in this case it was obvious that the problem was the video RAM, megadoctor can sometimes even distinguish between the symptoms of a faulty chip and a damaged PCB trace, or identify exactly which chip or trace is defective. I'm glad to see that megadoctor is doing its job

@krikzz @leo__oliveira If mega doctor is already testing DMA and reading back VRAM. Would it be possible to add some Sega CD tests like Word RAM DMA. I have some system combinations mostly with Fujitsu ASICs with graphical errors on a Sega CD, but all diagnostics pass.

@leo__oliveira It would probably be possible to run the DMA test after all the other tests, and if the system hangs at that stage or data copy errors occur, it would indicate a problem with the signals involved in DMA operation.

@heathy1337 @PointerFunction I knew someone had to have done it before, might be easier to find 2MB chips on old gpus too, using CS0 as another address line then ANDing the two for the new CS is very elegant.

@RGBeter32X @PointerFunction See here, I even made a quick tutorial: (For both the 16mb ram and 2mb VRAM) archive.org/details/pu18_1…

Found out it's possible to upgrade the VRAM on most PS1s. Stack two SGRAMs except for pin 28, solder a 22Ω resistor onto pin 28 and wire that to pin 121 of the GPU. Thanks @PointerFunction for helping me test it. Hopefully someone can make use of it.

@AversiveC @PointerFunction Got tempted by an unused chip select line. No PS1 homebrew uses it right now. Namco system 12 does though.

@RGBeter32X @PointerFunction …ok, but why? For home brew roms?

@gaab75 @PointerFunction Here's the link to what I was pointed to and used: github.com/spicyjpeg/ps1-…

@RGBeter32X @PointerFunction Is that test program available for download?

@shmoopyyyy @PointerFunction Nope! Nobody's made any homebrew (to my knowledge) that supports it yet, really just wanted to write it down so the info was out there. Namco system 12 used 2MB of VRAM+2MB of work ram (same amount of work ram as stock) so maybe some ports are possible in higher quality.

@RGBeter32X @PointerFunction is this mod useful? are there games that take advantage of the increased vram?

@Jackhead_ASG @PointerFunction Yes but it'll work on most PS1s, late PU8 through to some early PSONEs. As long as you DON'T have CXD9500 or CXD8514 as your GPU.

@RGBeter32X @PointerFunction Was the mod done on a PU18?

@Dean_Woodyatt @leo__oliveira @PointerFunction Kinda sorta, there were some talks in a server where it was mentioned VRAM would be useful, and I went looking into system 12 to find it. Supposedly a few others have done it before and nothing really uses it yet.

@RGBeter32X @leo__oliveira @PointerFunction Hmm, was there a YouTube video recently that may have inspired this upgrade thought :-p

@leo__oliveira @zaxour @jeffqchen Absolute worst case, 150 ohms is the same E series as 68, for the AES, the extra cent would be doable. Then snk DID get 75 ohm resistors for 3-5. I hate the input divider more though, 1.5v max is way above the 1vpp in the datasheet.

@zaxour @RGBeter32X @jeffqchen Made to order resitors did exist at the time, what didn't was the will to procure them at SNK.

I had no idea the DAC and encoder circuit on the Neo Geo AES was so terrible..... Binary weighted DAC without proper resistor ratios, resulting in poor linearity Encoder inputs driven WAY too hot (1.3-1.5V) 68 ohm series output resistance on some units (reflections!)

@leo__oliveira @zaxour @jeffqchen To ME the worse issue is that, looking at the schematic, it looks like AES overdrives the 1145, 5v*(3k/3k+6.8k)=1.5v, and older systems used a 2.2k instead resulting in 1.2v, which is still too hot for the 1145, then used 68 ohms instead of 75 on the output. Why did SNK do this?

@zaxour @jeffqchen It's about using the cheapest possible you can get away with, no? On the first AES model they used 100uf capacitors instead of the 470uf capacitors SONY recommended for the CXA1145 outputs...

@KytorIndustries At least the 1981 exists, and it wasn't the last of its kind.

Oh boy, the TI LM1881 has been marked EOL. Not great.

@illusionrip More interested in that PRO B0 😂

Alternative topshell for your future AES+ 😉 #neogeo #snk

Got tempted by a cheap MV4 and learned the hard way these are not fun to work on. That color ram chip tested good but led me to find PRO B0 is dead (PA5 is internally disconnected). If anyone has a source for one that'd be super helpful.

@zaxour That's a normal Fujitsu one, but the one in your more recent post looks different, when I showed Leo that kind of package on my X'eye he said it looked Yamaha.

@RGBeter32X They are all like this one here

Soon

@iVirtualPlays @Villahed94 Ironically a modern screen requires more parts to drive it, not less. Region is handled on main, you'd need to run wires to the jumpers to do that. Sub has a lot more freedom, at the expense that pretty much every custom chip can and should be replaced.

@RGBeter32X @Villahed94 I would love to see the Sub board also get replicated and customised. The Sega CD audio can be integrated into it along with a Region Free mod and all of the original circuitry cut out for the OG screen. I realised that the Oleg Endo board has been out of stock for a while.

Nomad Main is finally ready: github.com/RGBeter/SegaNo…

@iVirtualPlays @Villahed94 You gotta generate the gerbers yourself using KiCad, if enough people ask I can make some up and add to the repo. I have a set that JLC likes but different board houses might want them in different formats.

@RGBeter32X @Villahed94 That sounds awesome, how do I order this off of PCB Way or Osh Park? The files aren't working.

@iVirtualPlays @Villahed94 Yes, the MAIN board can. You can get all the parts from a VA1-1.8 or VA3 model 2. 315-5660, 315-5487, 315-5700 and 315-5708 are all pin compatible and can be used.

@RGBeter32X @Villahed94 Does that mean the Nomad can be built from scratch? Using parts from a Model 2?

@MathijsNilwik @Villahed94 I usually just, don't use the grid with repros, I set it to the minimum for most of them, and use free routing mode when I have to. Your reference becomes your scan, and what JLC will allow you to make.

@RGBeter32X @Villahed94 Nice work! I was working on a Venus MAIN replacement myself. One of the things what somehow stopped me with this project was the strange grid SEGA was using. Retracing the board is a a nightmare. How did you solve this?