The equals button does not work. Any soulution?

There is no equals button. Do you mean the ENTER button? Does it not do anything, but all of the other buttons work properly? Did you have any batteries leak acid inside the battery compartment?

When I found it today it was really corroded. Yes I do mean the enter button. I tried my best to clean it and I got most of it out. Any advice? If you can help me thank you! I'd love to get this working agsin

I had this same problem with my TI-81 and TI-82 a while back. I used a conductive ink pen to reconnect the corroded traces. I will have to disassemble my TI-81 and do the repair again, so I can write a tutorial on what to look for and how to fix it once I get some parts. The post I linked, despite being the relevant project thread, doesn't provide much detail. Basically, I used an X-Acto knife to scrape away the lacquer over the traces around where the damaged traces were to expose the copper, and drew over the damaged trace with a CircuitWriter pen. I filled corroded vias with conductive ink, as that was one of the more damaged areas in my TI-81. To protect the traces, I covered them with Scotch tape; it's not the best solution, but it's easy to undo and hasn't failed since I made the post nearly three years ago. If the traces aren't covered, the key mat will wear the ink away.

where do you get the circuit marker?

You can find them online for about $25. Cost tends to vary with the price of silver. I got mine at RadioShack for $30, but online is probably cheaper. Make sure you aren't buying a sealer pen instead of the conductive ink pen, and don't buy them used.