Acknowledgements – ZX sizif 512K Project – all credits to Eugene Lozovoy.
The first order is to get the PCB made; the Gerber files are readily available on Github; make sure you choose the latest version (rev.D1). I used JLCPCB to manufacture the PCB as I am familiar with them. The boards came in under a week.
Sourcing for components isn’t that easy; with the rising cost of chips, an EPM1270 cost SGD$70, the video encoder about SGD$25 on major online electronics distributors. To keep the cost low, almost everything I ordered was from China auction sites (Taobao); the problem with these sites is that there is a risk the chips are a dud, remarked or a total fake.
In total, based on the BOM, I ordered all the parts from 20 plus vendors; 3 or more pieces for ICs from different vendors if available.
- CPU – Z84C0020PEC – these are all used at about $3 each, modern version for the Z80A, likely remarked from old Z80As. Out of 3 pieces 1 is a dud, the other 2 works fine.
- RAM – AS6C4008-55PCN – used static RAM for about $4 each, ordered 5, 2 not working.
- ROM – SST39F040 – used Flash ROM about $2 a piece, ordered 3 pieces all working.
- Sound Chip – AY-3-8910 – These are hard to source in China, ordered 3 pieces all dead. Still cannot find a good source for it.
- Video Encoder – AD724 – These are still in prodcution, got it as new chips, no issues with them.
- ULA – EMP1270 – These are new parts, most sellers won’t ship without you commiting to a minimum order, need some back and forth wtih sellers to get it.
The rest of the parts are ok, except the 28Mhz crystal; it is sold without specifications that causes issues during the build.
Connectors and switches are a hit and miss; you buy them by looking at the picture of the item, which some might be misleading; most of them fit, but they gave me a short tactile switch instead of the long one.
The keyboard connectors are from Digikey; it would be tough to get them from China. It might be cheaper to get it from the regular UK retro parts vendors.