Help! Brown/Yellow Spots
 

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.
Strangely, despite the fact that the leaves are doing poorly, it put out two new flower spikes within this week. Oy. I'm so confused.
Thanks for any help you can offer!!!

It looks like it's a fungal attack.
I would trim off the affected leaves. Identify the brown spot area closest to the base of the leaves, then cut at least one inch away from that area into healthy tissue.

If you leave them as they are, the fungal spores will continue to spread and these annoying spots will be everywhere! stop it early helps.

Some of my oncidiums are affected by these fungal problems. I usually cut affected leaves off and then spray the affected plants.
Unfortunately, over time, these fungal problems find their way back.

It's just that different fungal disease have different stuff that works well to fight against, and just by looking we don't know what fungus is being a bad boy.

Since yours is affected on the new leaves, I think trimming off should take care of the problem.

Many people here just take spotting on oncidiums as natural part of their life as it is so common, or they simply just given up on them.

Funny thing is that these plants seem to grow and flower fine even with the spottings as long as spotting issue does not get too serious.

I personally do not like to see spots and potentail spread of these issues on to my other orchids freaks me out, so I take spotting very seriously.

What fungicide to use?
 

Wow. Thank you both so much.
I have other orchids, and so I am pretty freaked out.
Could you suggest a fungicide?
I will trim the plants ASAP.
Thank you!!!

Well, I try not to use chemicals. I normally cut spots that progress rather fast. Usually that takes care of the problem for a while.
If the same spotting issue comes back, then either toss the plant or do something about it (only if the affected plants are valube or rare variety).
There are lots of different chemicals to control fungal diseases, but for home use, I think there are about two, cleary 3336 and Thiomyl.
It is recommended that different chemicals are used each time to keep the resistance as low as possible.

For tiny black spots that do not seem to spread, I just leave them unless there are way too many and ugly to look at.