When I was testing all of my Atari 2600 games for that auction, I found several that were bad. All of the carts USED to work, but after a decade or so I found several that don't work any more.
First up is Shootin' Gallery. This has a mask ROM and bits 1/2 are both stuck "high" for every location. I dumped it and that's what was wrong.
Next was Strategy-X. This game had a bad mask ROM too. 4 or 8 of the locations near the end of the ROM are bad. The symptom was the game would sorta work but was all screwy.
Finally is Time Pilot and Smurfs Save the Day. Both do not work on the 7800. I resurrected my ancient Atari 2600 cart dumper I made some time in 1995 or 96 and fired it up and tried to dump both of those games, and both came back as 4K instead of 8K.
These two games use the same PCB inside, and have an EPROM along with 4 TTL chips to do F8 style bankswitching. There was quite a bit of corrosion on the PCBs, so I decided to desolder the 4 TTL chips, clean the board and solder new chips on I had laying around for fun.
I also traced the circuit out to see how they did it. Not too surprising but interesting they made a set/reset FF out of two cross coupled NOR gates instead of using a flipflop.
After all this, I checked with the meter to make sure there were no open routes, and fired both of them back up on the 7800.. still nothing! Dumping the boards again produced the same result- 4K of ROM data only, and the carts seemed to be triggering on 1FF6/1FF7 instead of 1FF8/1FF9!
I finally broke out the 2600 and tried both on there and they work fine! I read up about which games were incompatible with the 7800 and sure enough, one of those games is Time Pilot. My Smurfs Save the Day doesn't work on the 7800 either, and both use the same board so I'm guessing maybe the problem is with the circuit design itself instead of the game data.
Does anyone else have Smurfs Save the Day and a 7800 and can test to see if it (and maybe Time Pilot) work?
Thought I'd post what I found in case someone else found it useful or informative.