I've had this question for many years now. I'm hoping someone far brighter than I can offer me an explanation. I have a Australian PAL MegaDrive, model 1600-03, which exactly matches the descriptions here: http://info.sonicretro.org/Sega_Mega_Drive..._New_Zealand.29 http://en.wikipedia.org/wiki/Variations_of...and_New_Zealand It was purchased new back in 1992, and still to this day plays most MD titles flawlessly. The only titles it can't play are the Sonic the Hedgehog series (tested 1, 2, 3 and Sonic&Knuckles). Symptoms when running Sonic games include (and these happen totally at random points in the games - sometimes combined, and sometimes independent): game crashing (hard lock and/or black screen), graphic/sprite errors, sound errors ("crunchy" sound, or corrupt samples), no sound at all, and occasionally the total inability to boot the system at all while the Sonic cart is plugged in. Again, this is limited ONLY to Sonic games. I've tested a number of other titles over the last 17 years and they work fine. Similarly, I've bought other PAL MD units over the years (a 1601-03, and several MD2 units) and they play the Sonic games perfectly. At first I thought it was the Sonic cartridge I purchased in 1992. I had it replaced under warranty days after purchase, and the effect was the same. As mentioned, when Sonic 2 was released, it had the same effect. Ditto for the other Sonic games over the years. I've collected multiple Sonic cartridges over the years, and the results are always the same. I've asked a wide variety of (usually self-confessed) technical people why this might occur. The answers I've had range from dubious to plausible, but never with any backing of technical explanation. The dubious include people claiming the Sonic games "overclock" the MD unit to provide the speed the game needs (I know MDs can be overclocked, but AFAIK it requires a physical replacement of the oscillator onboard). The plausible explanations include people claiming Sonic "exploits" certain hardware functions of the CPU to leverage functions and features outside of conventional programming. This sort of thing is well known across other hardware and software in the console world, but again doesn't give any insight into actual specifics in this particular case. I also know that at least one other game is known to have problems with certain versions of MD hardware. Back in the day the PAL publishers of "Populous" issued a statement saying that the first release of their game had issues with certain MegaDrives, and that they would replace the cartridge for those that had issues. I've not had the chance to test a PAL version of Populous on my various MD units, however. So can anyone shed light on why the Sonic games don't like my 1600-03? Does anyone know specifically if there are low-level differences between the 1600-03 and other models that would specifically affect Sonic titles? And if so, what are they? Or is it just a simple case of my console being faulty? But if so, what ultra-specific fault would affect only Sonic titles, and not any other game? Does Sonic just push the MD harder than the "average" game, and the M68K on board is a bit flaky? Again, this is a question I've had for almost two decades now. If anyone could offer explanations, I'd appreciate it greatly. If I ever get the time (a luxury I'm very short on these days), I'm tempted to replace the M68K and oscillator of my 1600-03 with newer chips to see if the problem goes away. I much prefer my original MD1 for both audio and video quality (the MD2 units seem to use really nasty parts). But it would be interesting to see if that solves the issue.