If you have an Issue 1 ZX Spectrum that does not have its 32K daughterboard, and you wish to use it as Sir Clive (or at least Richard Altwasser) intended, it is relatively easy to construct a DIY 32K version using a 62256 static RAM IC and a single 74LS00 logic IC.
- Suitably sized perfboard
- Soldering iron
- 62256 static RAM (Farnell link)
- 74LS00 logic IC (Farnell link)
- Pin header strips (Farnell link)
- Kynar wire or similar
Step 1: Planning
The schematic for the circuit you are about to implement is as follows:
The pinout of the daughterboard sockets on the Issue 1 PCB are as follows:
Start off by cutting your pin header strips to size and inserting them into the PCB sockets. You can then trial fit some perfboard and trim to fit.
Once you have a suitably sized piece of perfboard with headers in place, you can solder these in, making sure they don’t fall out of place. Don’t be afraid to trial fit before and after each header strip is soldered.
Step 2: Wiring the circuit
A certain amount of proficiency is assumed here, in order to perform the point to point wiring required by the schematic. Once complete, you should end up with something like this:
Step 3: Testing
Carefully insert the new daughterboard into the PCB sockets, and perform checks with a multimeter to verify that there are no shorts to ground or 5v of the address/data/control lines according to the schematic and layout. If all is well you can power on, and test if you have your full 48K of RAM either by verifying that PRINT PEEK 23733 is 255, or by using your favourite diagnostic program:
Once you’re satisfied all is well, apply some hot glue to any loose wires to hold them in place, reassemble the machine and enjoy your newly expanded Issue 1.