Zerosquare

https://en.wikipedia.org/wiki/Metroidvania

If your cartridge connector has poor or dirty contacts on the EEPROM pins, the EEPROM contents can be corrupted, which can cause scores to be erased.

I don't have one, but from I understand, it should work the same.

Spinner mode isn't enabled by default in Tempest 2000. See the "Enable Rotary Mode in Tempest 2000" paragraph on this page: https://www.retrorgb.com/jaguartempest.html You only have to do it once -- the setting is saved in the cartridge.

Since the (S)catbox includes networking, it probably drives the UARTI signal all the time. And according to @SainT, the JagGD needs UART communication to work. Unfortunately, the way the Jaguar is designed means that the UART signal from the DSP port has precedence over the one from the cartridge. One way to fix it would be to modify the Scatbox to add a switch in series with pin 3B:

Unfortunately, it doesn't seem to happen to copies of Supercross 3D.

♫ Albert's making a list, and checking it twice... ♫

Club Drive is so ridiculous it can be fun if you don't take it seriously, and the design has a few interesting ideas. Checkered Flag is just... tedious.

Spoiler: it never does.

I hope it's just a capacitor problem. I had a Jaguar with similar crashing and audio issues that I couldn't fix - replacing the capacitors didn't help.

Upon seeing Checkered Flag for a first time, a friend who's a Megadrive fan described it as "this is basically Virtua Racing, but done wrong". So it's pretty surprising you like it, given how much worse it is compared to the "original".

Try converting the files into ROMs using Jiffi: http://reboot.untergrund.net/new-reboot/jiffi.html

I doubt CJ's ports include any original TOS code ; there would be little reason to, when rewriting the few TOS functions games actually use is both simpler and use less ROM space.

The internal UARTI signal is connected directly to the expansion port, but is connected to cart pin B30 thru a 1k resistor. So in theory, if the device connected to the expansion port has strong enough output drivers, it should override the JagGD's signal. Maybe it could be possible to make "buffered" JagLink adapters for people who already bought a JagGD. (They'd have to hotplug it after launching the game, if the GameGD needs UART comms to run the menu.)

Does installing a reset switch on the console itself work? Or would it just restart the current game?

I'm pretty sure LinkoVitch's interpretation of the pointer rules is correct, and that it's not where the problem is. The documentation has an interesting paragraph about the CLUT:

Mouse support requires reading the joystick registers very frequently (ideally about 2000 times per second), as opposed to only once per frame for the standard joypad. It may not be easy to integrate this into the Doom source code without causing performance impacts. Still, an interesting idea indeed.

The BJL ROM is free and can boot games:

You don't need the boot ROM to run games anyways. The only thing it does is initialize the hardware, check the cartridge's digital signature and display the boot animation.

If you say so. Why don't you port a NeoGeo game to the Jaguar and show all of us wrong?

...if you're willing to disregard the massive difference in price, both for the system and the cartridges. And the fact that this difference is the reason why the NeoGeo hardware could achieve what it did back in 1990 or so. Because its design is closer to the Jaguar hardware: it doesn't require huge ROMs with fast and random access, instead the graphics data is loaded from CD-ROM and kept in RAM. A cartridge Jaguar game would load it from ROM instead (so the load time is negligible), but once it's done, the result is the same. My point is: don't expect the Jaguar to achieve what the NeoGeo CD couldn't do, despite having twice as much dedicated memory than the Jaguar has in total. I could, if I had hours or days to spend doing benchmarking on both machines. Which I don't. But I could ask the same: where's your data? What code have you written on the Jaguar? Constraints on modern hardware are completely different from constraints on retro hardware, so the comparison makes little sense. SNK didn't use the multiple bus approach just because they were lazy. They used it because they couldn't have achieved the same performance otherwise.

If you want to compare the Jaguar to the NeoGeo, you should compare it to the NeoGeo CD. The latter has 4 MB of RAM just for the graphics and several separate busses (while the Jaguar's total amount of RAM is only 2 MB, with a single bus). And even with that, it can't pull off all of the cartridge-based NeoGeo games.

You still need the original custom chips. Best Electronics sells them, but I don't know how much they have left, nor how expensive they are.

I disagree. There are several rB+ games that are more fun to play than some of the commercial releases.