Hi
I’m not too familiar with casio keyboards but I have worked on Roland’s and a couple other brands and here’s what I usually find works:
When you say you cleaned the contacts that usually work but only if it has gold plated contacts
If they are black that means that they are carbon contacts and to help them work you need to clean them then get a pencil and draw some carbon dust back onto it to help it become more responsive
If that doesn’t work I would start looking towards the main board and have a look for anything off looking (for example burned or blown components or corrosion) as it could be a dodgy or faulty component on the board that may need replacing or you could just replace the whole board and sell the old one for parts
If the above doesn’t work please let me know and we can further look into your issue
Hopefully this helps
Any questions please ask
Thanks:-)