A new way to replace the ZX Spectrum ROM without modifying the motherboard.
With this simple adapter, you can install a 27C256 in place of the original 128 ROM, allowing two ROM images to be stored in the memory.
This means you can use both the original ROM and a diagnostic ROM in the same chip, and select between them using a switch.
Construction:
The build is simple. First, solder the passive components such as diodes and resistors. Then solder the headers for connection to the motherboard.
Finally, solder the EPROM directly, without using a socket.
There is very little space under the keyboard, and using a socket would raise the EPROM too high, making it impossible to close the case.
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Components:
R1,R2: 10K Ω
D1,D2: 1N4148
U1: AT27C256
Video: youtu.be/FNNIXsdO9ps