I don't have access to an actual 78 PCB to go hands on, but i can say that in your top image it's likely the 2nd largest chip is the flash memory module (marked Samsung). The largest one is certainly the CPU, marked Garmin & ARM. The third largest is probably the RAM module. If you are intending to replace the flash chip you can do so using a scavenged part from a similar donor board or google the part number to source a compatible new replacement but as i said doing the actual replacement isn't hard for an electronics tech, it's then re-programming the new chip for the individual device that's the problem.

You can read more about successfully replacing a failed flash chip in a nuvi 1410 with one from a nuvi 205 (related series, similar PCB) in this thread here: [Only registered and activated users can see links. ]. In that case the chip was only required to be reflashed with the correct fw to work. That's because the region layout is the same and so full reprogramming wasn't required.

It's not feasible or even appropriate to give detailed guidance for such a delicate procedure here of course. I recall reading some years ago about a tech from a (non-official, perhaps) Garmin repair centre in Eastern Europe who managed to replace a failed flash chip with a microSD using jumper wires from its board connections to the card somehow. No idea how that's possible but maybe the card was the same brand as the chip and had same controller, etc .... Dunno really, but he'd have needed to reprogram it for sure.