Y-unit boards not only have security PAL chips on them, but I've also found that they have wire jumpers on the solder side too... I tried switching around my bad Smash TV to a MK board and started listening to people on here about jumpering resistors and wound up fucking up the RAMs on two different boards. that's when I noticed the jumper wires on the back, they run to various roms and PAL chips. I just never bothered trying to match up the jumpers the same.
the T-unit shit's all interchangeable, I guess. the small chip numbers are all the same on my MK1, MK2 and NBA Jam... kinda weird that Midway did that, but only really 3 games were ever made for it, and I already listed them, and NBA Jam TE. the noticeable differences are that NBA Jam has the Player 4 header and MK2 will have the memory board sockets, so maybe that's how they schemed it. lol