SOS--Brown Spots on Leaves

[twostride]

Hi! I'm a newish orchid person. This is my first post, so hello everyone. I wish I were writing under better circumstances!
I just divided an orchid for the first time, one I have had for two years and had outgrown its pot (plus, I suspected the material had broken down).
Upon repotting, one part is doing quite well, while the other is developing brown spots on its leaves. What do I do? I know the pot I put it into is a bit too big. But is that really what has caused this? It has only been in its new pot for about a week. Most of the spots are showing up on the newest growth.
Thanks for any help you can offer!!!