It looks like the FB2's HMOVE circuit isn't fully bug-compatible with the TIA.
I'm kinda thinking that way now too, a multicart based on a CMOS eprom shouldn't care about a 4.2v VCC and the wires weren't that long. Other people have posted and sent PMs along that line. Here are screenshots of Galaxian and Cosmic Ark, I'm not sure the TIA circuit is all there (still a great product for the price though).
OK....I have worked on TIA myself....not the one in Flashback, but one for the public to use since I wasn't too thrilled with the "public" one being pulled a few years ago. I am in no way complaining about Flashback 2....in fact, I friggin LOVE the machine...for $30 the case and the joysticks are worth that alone! Moreover, I am begging you not to interpret this criticsm or me bashing "competition" ... I am not that petty (except when it comes to that friggin "RetroGames" design...sorry).
My best guess is that there are problems due to the designers using a lot of asynchronous logic and not closing timing properly. In fact, I would bet that they simply copied the schematics without taking a more modern CMOS process into consideration. Moreover, if there is process drift, you'll see strange behavior from chip to chip. You can use a lot of async. logic (by this I mean latches and the like) and get *something* to work...however, if something gets routed differently when building the chip or if temperature changes or if the process changes, you will get a broken circuit. Trust me...one build I had, if certain clear signals were not routed on global routing in FPGAs, you'd get really cool things happening like the lower 40 scanlines of pitfall being skewed and the like...
My FPGA solution seems to be very stable now (actually has been for the past two months)...it was not until I made everything synchronous and spent hours of debugging every little friggin detail in TIA. I kid you not, if you don't get the timing down perfect on every single subcircuit, throw out your design....it will break with one of the 500+ games out there. These programmers exploited evry little nook and cranny of that chip. Moreover, you absolutely need a debugger like Z26 running on the side to verify every single cycle....I cannot see how anyone could develop a chip without paying that much attention to detail. I was a 1/2 cycle off on HMOVE circuitry once that broke Enduro!
So, for a $30 product, buy about 6 Flashbacks...I guarantee you the next one will be even better...this thing will sell a ton regardless. They are going to be awesome Christmas gifts and nobody should think they'll be disappointed with it! Think about what you are getting for the $30....two brand new, quality joysticks, a killer case, and 40 (well in my case 39) games that are pretty much dead on!
However, I don't think you should get your hopes up thinking that you can make portables out of this. I am sure compatibility will be sky high of 75% of the games...however, based on the problems I have seen, I don't think 100% compatibility is a reality.
Finally, please take none of this as bashing of the chip...there were deadlines and schedules to meet...trust me...working for big companies suck.
PS Yes, I will get my FPGA solution out there...please have patience...and no, I am not going the "pirate your ass of with a USB interface"....but close ;P ! I am hoping the developers will like some of the features I am adding...
PPS As a quick test, try spraying some electronics freeze spray on the new 2600 chip with Galaxian running....I am half tempted to try that with my buggy Secret Quest and Radar Lock....that might fix the problem in the near term for a few frames...