I tried both Kool Aid Man ROMs listed here at AA (NTSC & PAL) and both are not playable on my "Production" model. Yes, you have to hit the game reset button to start the game on real hardware, but if you hit the reset button on the portable, it goes to the Kool Aid Man crashing into the wall scene. Once the game starts, Kool Aid Man is stuck in the upper left hand corner and is not playable.
Kevin, is yours a "Pre-Production" model? Maybe that's why it works on yours?
No, mine is a production model, but with the screen swapped out from a Genesis portable. It looks to me like the same screen was used in the Genesis portable as in the pre-production Atari portables, and yes, the screens are interchangeable (as mine demonstrates). However, I have the same screen migration issues with the larger screen as with the smaller production screen. We need someone who has both models to compare the PCBs, as I suspect they were changed. It could be a software change, but I'm guessing there's a hardware change that if we can spot, perhaps we can modify to be like the pre-production models for better compatibility.
Does that same happen for the Kool Aid Man Hack that fixed the glitch when Stella was a young'un?
I just ran a compare of that hack with the ROM that was on my SD card, and they are the same. I may have unknowingly picked up that ROM in the past, but I could have sworn it was the one from the ROM pack uploaded by DoctorClu in the other Flashback Portable thread. Anyway, that ROM works.