Mission Complete!! After doing extensive testing during the weekend, I can confirm that the capacitor replacement completely fixed all the audio issues. I ran trough every game at least a couple of minutes (including Xeno Crisis and Hypernoid), played a lot of matches of Windjammers, Neo Turf Masters, Baseball Stars 2 and League Bowling, and completed the whole Metal Slug series. All of this without any single audio issue, system crash/freeze/reboot, or visual glitch. Everything is 100% perfect and stable now.
Regarding the original capacitors, I measured them and both are 49pF, so if they are supposed to be 47pF, the value is correct. Maybe they are low quality and another parameters, as the ESR, are off, I can't tell. I just think that some combinations of cartridge and MVS (mine is a MV1ACHX) may require a bigger value to fine tune the timing, but it is just an assumption.
I found this to be a very enjoyable and rewarding mod, as long as you have the required tools and skills (could be very frustrating otherwise). Cause of this, I would like to share some tips and ideas of the process, I hope this can help someone in the future, both on the hardware, and the software side.
On the hardware side
- The most frustrating part of the process, for me, was extracting the daughterboards. The good thing, is that there is no need to be much careful at this step. The daughterboard can be completely destroyed on the process without any problem, as new ones can be made easily, as long as the main board and the flash chip are not destroyed on the process (which is very difficult, as the heat is applied on the bottom side of the board, an the chip is on the top side side of the daughterboard, there is a big gap for the heat to dissipate). Building new daughterboads, with new gold plated pin strips, is recommended in any case, because the old daughterboards with tin leftovers on the pins are very likely to have connection issues with the female headers. When I did the mod, I totally destroyed one the daughterboards and slightly damaged the other two, but I was going to build new ones anyway.
- Several pages before, there was discussion about what vacuum de-soldering gun and what nozzles to use. My answer here is clear: none. I don't recommend to use a vacuum de-soldering gun at all, I don't even have one, as I don't like them much. For extracting the daughterboard, use a hot air soldering station and the process described by @rewrite here (https://www.arcade-projects.com/thr...lticart-upgrade-build-guide.27994/post-404691). The preheating station is no really needed, it will make the extraction process easier, that's for sure, but not strictly needed (I don't have one). Once the daughterboards have been extracted, for removing the tin leftovers inside the holes, I keep heating with the air station and when the tin is melted, I quickly put my mouth as close as I can above the board and throw a short but intense blow (I know, not very professional, but it works nicely). By this method you can easily clean 2x5 holes per blow, but be careful because the tin will fall on the table. With and air compressor maybe this can be done quicker and easier, I didn't test it as I don't have a compressor.
- For the new daughterboards, the mangled castellated holes doesn't need to be fixed, as they can be soldered just the way they are, but I found that fixing them, although time consuming, is worth it, cause it makes soldering the chip easier and gives better results. For fixing them, I put them on a solid and stable surface and, with a very sharp surgeon knife, I made two well directed and firm cuts, on both sides of the holes, to cleanly rip the unneeded half of the ring. If doing this, always check with a microscope or magnifying lens that there are no bridges between the castellated holes.
- After soldering the 22x2 male pin stripes on the daughterboard, check that all the pins are correctly aligned and if not, align them with fine tweezers, before inserting them on the female header. These connectors are very flaky and the heat applied while soldering is very likely to slightly unalign them. I didn't check this on my first daughterboard and partially damaged one hole of the female header when trying to insert it. Luckily I was able to put it back in place and didn't have to replace the whole header. Also, before inserting the daughterboard in the female header, be sure that there are no flux leftovers on the pins, as it could cause connections issues later, and could very hard to clean inside the holes.
- This point is important, I mentioned it before. If after completing the mod everything works fine, but there are occasional sound issues, in the form of wrong or louder notes, or missing or incomplete sound samples, remove capacitors C4 and C5 on the PROG board and replace them with new 100pF ceramic capacitors. This totally fixed the issue for me.
- Another important point, if your MVS board has the M68K NEOBUF replaced with a FPC yellow bridge, is very likely to cause troubles. When I bought my first 161-in-1 several years ago, I had very frequent crashes and reboots, and I got them totally fixed by replacing the bridge with a NEOBUF equivalent PCB. I mean replacing this (https://wiki.neogeodev.org/index.php?title=File:Neo-buf_bypass.jpg), with this (https://www.tindie.com/products/furrtek/neo-buf-replacement/).
- And last, but not least, I HIGHLY recommend using a good digital microscope for this work. It can be done without one if you have good eyesight, I did similar jobs on the past, but my eyes are not as good as they used to be, and now that I have a microscope, the difference is like day and night. It makes everything much less frustrating, and very easy to spot and fix mistakes like shorts, bridges or unsoldered pins. Also it is nice for taking pictures and videos, for documenting purposes. I use one like this: https://es.aliexpress.com/item/4000901809079.html
On the software side
- A few pages ago, before I started the mod, I launched a question about the compilation of the CPLDs code, but I didn't get a clear answer, so I had to test myself. Depending on the number of games and how they are sorted on the list, Quartus may give an error about not being able to fit the CPLD code. In that case, just change the fitting strategy from Speed to Area, it is totally safe to do it and won't cause any issue. The option is in "Assignments -> Settings -> Analysis & Synthesis Settings".
- For the ROMs, I made the following modifications:
- For KOF 2000, I used the ROM Kof2000nrxfix.zip from this post (https://www.arcade-projects.com/thr...rtridge-to-change-rom-games.15069/post-409161). It still has S layer corruption, but texts are far more readable, and in-battle graphics are almost perfect. This is maybe the best we can get. To use this ROM take S, M and P (concatenate p1 and p2 together) from the mentioned ZIP file, and C and V from the kof2000b ROM on the Vortex archive.org repository.
- For Garou MotW, the prototype is the best we can get, but I found a patch for the P ROM that fixes the crash when doing the Kim Jae Hoon TOP attack, plus other minor cosmetic changes to make it look closer to the final version. The ending sequences are still missing, and the Tizoc Arena TV monitor glitch is still present, but the game is 100% playable. I will attach a xdelta patch at the end of this post, for the P ROM of the garuoub ROM set on the Vortex archive.org repository.
- For Irritating Maze, I found a patch that allows the game to be controlled with the directional stick, plus B, C and D buttons to change the speed of the rod. Is not the ideal way to play this game, but at least is playable, otherwise this game is totally useless. I will attach a xdelta patch at the end of this post, for the P ROM of the irrmaze ROM set on the Vortex archive.org repository.
That's everything that comes to my mind right now, but if anyone is currently doing the mod, or is trying to decide if do it or not, and have any questions, feel free to ask. I will try to do my best to help, as the rest of the users on this thread.
Finally I would like to share some pictures of the process, as they can help another users to have things clearer, and the mentioned xdelta patches.
