I am putting these games back together, and I discovered a factory test for doraemon. If pin 35 is grounded (pulled high) at power-up it will go through a display and audio test. There's a pad connected to the pin but it doesn't go anywhere, so it looked highly suspicious. turned out I was right.
Speaking of test modes, when I was little I found a sound test of sorts in the first Konami TMNT LCD handheld, which would play every sound one after the other in a loop. You can easily access it by fiddling with the batteries so that there's just a brief power cut, but there may be a more official way to access it as in the Doraemon game.
So... whenever those handhelds are supported, that may be something to look into.
