I've not even seen one of them.
Best thing to do is crack it open and start probing.
Most Vtech's will either have a clock control resistor or coil.
If it's a res, you can do the pitch drop/raise by removing and replacing it with a potentiometer.
If it has a coil, it will more than likely glitch out.
It's all trial and error but you should just dive right in.
It's the best way to learn.
