Modification to a COCO 2 model 26-3026 to go from 16K to 64K RAM memory
I had a COCO 2 with 16K RAM memory. I wanted to updgrade it to 64K. So here is the modification I made. My board was from a model 26-3026. This board has 8 chips of DRAM with 1-bit data line. So obviously they are really 16 kilobits memory. Basically the modification consists two things: remove the 16 kilobits chips and replace by 64 kilobits change and second thing is to add a jumper connection in a position labeled W1.
The chip to replace were in sockets in my case and they are located under the keyboard. So first, we need to remove them from their socket.
Then, place the 64 kilobits chips.
The original 16 kilobits memory chip were labeled "8040517" and it is apparently a "Tandy house number" as a regular 16 kilobits chip at this moment was the 4116 and 4116 needs so special voltages and not working only on a single 5V supply like the 8040517 chip and also like the new one to install, the 64 kilobits, with 4064 part number.
The other modification to do after is to solder a jumper wire and make a solder bridge between two pads on the board so the software is aware that 64kilobits chips are installed.