One thing I just found which is a bit strange with the one GB Boy I kept to test, in Pokemon Yellow the all music is completely wrong, the lower notes seem to be right, but the mid and high notes are way off in timing and pitch.
This isn't the cart as I tested it in a GBC and it was fine, I also tested Pokemon Red and Blue both of which the music was correct in both GBC and GB Boy, I tested the same Yellow cart in an old built in games GB Boy I had and it doesn't do this.
I don't have any others in stock atm and it'll be a few weeks before my next lot comes through, can anyone else perhaps test Pokemon Yellow on their GB Boy (not a built in games model) also and post the results?
The biggest giveaway is when you are on your Bicycle, but all the other music is wrong also.
I'm just wanting to know if this is an isolated problem with this particular GB Boy or if they might all be this way.
EDIT: Never mind, for some reason when this cart is used in the GB Boy it sets the sound option to earphone 1 every time on boot, thus cutting out the left channel.
Paid.