Thanks @Deadeye for your pics, I got my tester yesterday.
I’m planning to solder an arduino on to of the existing controller, just to be revertible if it doesn’t work.
For reference, I attached a datasheet overlay on your pics, I hope I got the pins right.
The chip on the keyboard says HS6620 and the datasheet is HS6620D, but it seems to have the same pins.
I just have to sort to which rows/cols out each GPIO correspond.
