I'm not sure which model you're talking about. Not a lot is known about the circuit boards. Actually, the circuit board may be different between two of the same model, depending on when or where you bought them.
The V5 & Familitchi have the same function, but some have region-assignment jumpers, and some don't. I've seen three different circuit boards. The ones from North America, and from Asia/Australia have jumpers, but the one from UK doesn't. (The region-assignment jumpers can be used to set the region: North America, Asia/Australia, or Europe. On this model, you can get a special character by mating two from different regions.)
On the TMGC+C, Tamagotchi iD, and Tamagotchi iD L that I have, JP1 can be used to enable debug mode. (This may not be the case for different production batches, so don't blame me if you try something and it doesn't work, or you end up wrecking your Tamagotchi.) Some earlier Tamagotchi iD had the copper pads exposed, but the later ones have the copper pads painted over, so it's necessary to carefully remove this paint before you can set the jumper.