After a lot of work ( months of testing and modifications to the basic schematic ),

a final version of this 128Kb RAM expansion card appears. With the help of the great

technicians from PCBWay, i have a PCB that i can connect to a Cobra motherboard

( a thousand thanks to the artists of the PCBWay ) . This board converts a normal

64Kb Cobra into a 128Kb Spectrum +3 compatible one .

https://i.postimg.cc/xCjKTwWx/cablaj-01.jpg

https://i.postimg.cc/QtNpx2RY/cablaj-02.jpg

https://i.postimg.cc/26j48sPT/cablaj-03.png

https://i.postimg.cc/yd6FYMwv/cablaj-04.png

https://i.postimg.cc/tTrF1rbV/extensia-128k-cablaj.png

In short, the scheme is as follows :

https://i.postimg.cc/26HnqHYZ/extensia-128k-schema-001.png

https://i.postimg.cc/SsZcXZ4W/extensia-128k-schema-002.png

https://i.postimg.cc/Px61L6H1/extensia-128k-schema-003.png

for the following PCB :

https://i.postimg.cc/nzVvcy6W/cablaj-05.jpg

https://i.postimg.cc/W3pMbBQC/cablaj-06.jpg

https://i.postimg.cc/Jn7b4ffL/cablaj-07.jpg

https://i.postimg.cc/wvxhTCC8/cablaj-08.jpg

The gerbers are here :

https://drive.google.com/file/d/1flJjWZuWv7nqgZoccNkuzhdbcLaeFNVk/view?usp=sharing

I have prepared 2 boards : a "standard" version with normal sockets with blades

and a "DELUXE" version with augat pins, which I will connect to a Cobra that has

been waiting for this extension for a long time : 

https://i.postimg.cc/FRFjsMMh/cobra-01.jpg

https://i.postimg.cc/pTVDXwwr/cobra-02.jpg

Unfortunately, the project is still a work in progress and I will be back with the

PROM, GAL and EPROM loads, and other construction details after the project is completed :

https://i.postimg.cc/509wNhht/cobra-03.jpg

https://i.postimg.cc/fLHY3HsN/cobra-04.jpg

https://i.postimg.cc/vBP51Pym/cobra-05.jpg

https://i.postimg.cc/2jxCWVVM/cobra-06.jpg

https://i.postimg.cc/VsFztdd2/cobra-07.jpg

For more details please also look here :

https://nicuflorica.blogspot.com/2025/11/cobra-128k-compatibila-spectrum-3.html

PS : added BOM files ( bom.bom , bom.csv , bom.html , all 3 in zip file )

https://drive.google.com/file/d/1E7waXNFSTgD5srHs2fDv5t9bBLs378b2/view?usp=sharing

Many thanks for your patience .