im working on my Amiga 500. with a multimeter i measure 5 volts at the keys respective Y row pins on the keyboard ic when they are pressed. so i believe the switches are working
i replaced the keyboard pcb with a reported working one to rule out a problem with the keyboard ic and other electronics.
i swapped the cia chips to try to rule that out.
the system has an adram 540 ram expansion. i can try pulling that completely out.
but what should i check next?