Hey there,
This is my first time attempting to really clean or repair anything electronic, so perhaps I made some hasty first timer mistakes. Someone gave me a Yamaha Portatone PSR-540 that they bought in 2008 recently. I played around on it and found a significant number of dead keys, perhaps 20%, and decided to dive in and fix it. After watching a few videos on youtube of other keyboards, I began digging in and through a long painful process of lack of proper tools/discovering how to take this specific keyboard apart.. I did.

Here's what I did:
-Cleaned both contact strips with contact cleaner and a tack nonstick painting towel (the towel might have been an issue) and cotton swabs. I didn't use gloves for most of this (oops?).
-Removed all the keys and cleaned them with water, paper towel, cotton swab.
-Shook off the rubber contact strips
-Air dusted everything
-Wiped down all plastic insides with a paper towel for dust removal etc

I put it back together, and unfortunately now 85-90% of the keys are dead.

What could have gone wrong/how might I be able to salvage this?

I'm really at a loss right now.

 

get a used USB controller with MIDI.