It looks like things are not as bad as they looked a few days ago when I discovered the issue with the soldermaks in the keyboard combs. Have been thinking about solutions and tried Velostat (unsuccessfully). There is of course always the option for chemical treatment but I wanted to see first if there is some more user-friendly way. So the good old Microchip came to save the day once again :-)
Just received from them a box with sample chips for unrelated project. The chips have no connection here, but the box caught my attention, and especially the black foam inside.
So I took the scissors and cut two pieces to fit into the key holes in the PCB0 frame board. The miracle happened - the keys worked perfectly fine! In fact so well that I started feeling sorry that I was so quick to revise the board, and even considering whether to make this the standard way for building ELLO keyboards.
Obviously now the challenge in front of me - to identify where to buy this foam and more especially to have it with the right thickness (0.5-0.7mm) and cut into small square and rectangular pieces as per given specs. Searching and welcoming any information about it.
Getting really close to the finish now...