Zerosquare

Not to mention the elephant in the room: the JagGD already exists, and it doesn't require owning a JagCD in the first place. Sure, it doesn't work reliably for everyone (at least, not yet), but the real JagCDs don't either.

I can't find it at the moment, but I have the DOS version somewhere, and I'm almost certain that the CD case is the one shown in the upper picture. It also includes the same CD audio tracks that were featured on the Tempest 2000 soundtrack CD. I don't remember if the Windows version is on the CD as well. No idea on what's on the CD in the bottom picture.

You need this: https://hackaday.com/2022/09/26/tiny-dongle-brings-the-hard-drives-song-back-to-updated-retrocomputers/

That would work as well ; the contact that needs to be isolated is the third one from the left on the bottom side of the DSP port (when viewing the Jaguar from the back side). It may work, or may not if the board uses the +5V supply from the DSP port to power something else. Worth a try, anyways. I'd use a piece of paper instead of electrical tape, as the latter leaves sticky residues.

Okay, so there's two ways you can work around the issue: 1) unsolder the two ICs that handle networking: or 2) cut this track on the bottom of the board: Choose the one you're most comfortable with. Of course, in either case, networking won't work any more.

@Songbird: in case diagnosing the broken controllers is too time-consuming to be worth it for you, some people could be interested in buying them as non-working and getting a shot at fixing them themselves.

I don't think the jumpers on the bottom are for disabling the networking part ; they're too far from where the chips that handle those (U1 and the one to the left of it). With a good photo of the other side of the PCB, it'd be possible to figure out which component(s) should be removed to avoid the conflict.

No, the Jaguar wasn't popular enough for that. I think there's only one third-party pad that was released back in the day, but it's a 3-button one, and those who tried it say it's bad.

OpenMPT is a module tracker that can import MIDI files: https://openmpt.org/

The 93C46 is a 16-bit wide EEPROM. When read from/written to a binary file, there's no universal standard on which byte order should be used (MSB first or LSB first, aka big-endian or little-endian). So if your programming software has a setting for this (or something like "swap odd and even bytes"), try flipping it and reprogramming the chip to see if it helps.

Where did you buy the SD card from? If it's eBay or Amazon, the card may be a counterfeit (this happens regularly). You can use software like https://h2testw.org/ to check whether your card is working correctly.

The metal shield is for preventing radio interference, it's not used for cooling. I remember someone (probably SCPCD) mentioning that with the shield removed, nearby devices such as the JagCD could be affected and not always work correctly. I don't think the Jaguar itself was affected.

As long as there's clear distinction between : - what's officially documented - what's known to be wrong (i.e. it's been confirmed that real hardware doesn't work like that), with corrections - what's been conjectured by testing, but without definite proof that it works the same on all versions of the hardware (i.e. things that are officially documented as undefined or reserved, or not documented at all) I don't see the issue.

I'd suggest making the color palette "cyclical" if you can -- that is, making sure that entries #255 and #0 are almost the same, to eliminate those black fringes.