After a few (actually many) attempts, I can finally write to the EEPROM (AT28C64E) in a reliable way. It took some additional reading, reverse engineering and finding other’s schematics and sources.

I also got some help from Henry S. Courbis from ReactiveMicro.com/UltimateApple2.com. He pointed me to the right way to create the /CFFF latch. I used a 74LS74 flip-flop for the Set-Reset circuit, but had the D and Clk pins bound to ground, as I found it in numerous schematics.
Henry pointed me to the fact that he had to pull the D and Clk high. This actually did it and I can write now to the EEPROM to corresponding page, for the slot the card is in.

Apple II EEPROM POC

First test schematics (Proof of Concept)

Next step was to fully decode the $CFFF address using a 74HCT 133.

A2 EEPROM Logic Full Decode.png

Fully decoded $CFFF

This allowed me to read/write to/from the $C800-$CFFE ROM address range.

Next I found that the EEPROMs I ordered through AliExpress are counterfeit/defective. Writing to some addresses resulted in errors when verifying. This meant I had to order some other EEPROMS. Unfortunately the 28C64E aren’t produced anymore, so I had to settle with the 28C64B, which have a slightly slower write timing.

I ordered some PCBs and SMD parts, which I already have received. I soldered one card and programmed the EEPROM. I can say it is a success. (Although I had to cut two traces and lay some wires).

Next step is to implement /DEVSEL.