Yes: a ZX81-compatible computer could be built from newly sourced parts in 2022, but not by using the original custom ULA. The documented approach recreated that chip’s logic with 74-series components. It is a modern recreation, not a Sinclair-built ZX81, and a successful build depends on matching the project’s board files, component list, keyboard, clock circuit, video and power arrangements.
What the 2022 all-new-parts build changes
The original ZX81 relies on a custom Ferranti ULA, which the 2022 project account says was unobtainable for its build. Instead, the design reproduces the ULA’s functions with discrete 74-series logic. Hackaday describes the board as the size of the original and notes a separate tactile-switch keyboard PCB: Hackaday’s account of the 2022 build.
This substitution makes a new-parts recreation possible without sourcing the original custom chip. It does not mean every component is guaranteed to be available today, nor that a historical parts list is a turnkey current bill of materials. Builders still need to source and assemble the board, clock circuit, keyboard, connectors and case, and make compatible video and power choices.
Choose the right kind of build
| Approach | Logic replacement | Best suited to | Important distinction |
|---|---|---|---|
| 2022 all-new-parts build | Discrete 74-series logic replaces the original ULA | Recreating a ZX81-compatible computer from newly sourced parts | Use the exact project board files and bill-of-materials revision for the build. Source |
| ZX81+38 clone | Standard logic ICs replace the ULA | A DIY build using shared board, case and keyboard files | Motherboard and keyboard revisions must match; its author also documents a clock-circuit component correction. Project account |
| Issue 3 replacement board | CPLD replaces the ULA; the design also specifies a Z80A, 27C64 EPROM, 681000 SRAM and 74HC04 clock circuit | Repairing a faulty ULA machine or modernizing an existing ZX81 in an Issue 3-style layout | This is a separate redesign, not the same discrete-logic build. Replacement-board project |
| Packaged kit | Bundled ICs and other parts; the vendor page does not establish that it uses either recreation design | A buyer seeking a more complete supplied package | The page describes a 110 V supply and says UK/European supplies and manuals were unavailable there; current stock is unverified. Kit page |
Files, revisions and fabrication
The ZX81+38 project account says its shared materials include KiCAD design files, case and keyboard STL files, and information for ordering the keyboard PCB. That gives builders a path from board fabrication through enclosure and keyboard assembly, but file compatibility matters: the author reports that the keyboard connector layout changed with motherboard revision 1.9. The newer keyboard layout is intended for revision 1.9, while an earlier layout is described as better suited to motherboard revision 1.6. Check the repository and confirm the motherboard and keyboard revisions agree before ordering boards or printing parts. See the ZX81+38 build account.
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Clock-circuit example: why the BOM revision matters
In one ZX81+38 build account, the assembled computer initially showed a black screen because the clock was not being generated correctly. The builder traced the problem to two capacitor values carried over from an earlier bill of materials: 15 pF had been used, while the newer project version specified 4.7 pF. The builder reports that replacing them with the newer values restored the expected screen display. This is a specific account of one revision and one build, not a universal ZX81 component value or a guarantee that this fault will occur. Project account.
When a CPLD replacement board makes more sense
The separate Issue 3 replacement-board project takes a different route from the 74-series recreation: it uses a CPLD in place of the ULA and lists a Z80A CPU, 27C64 EPROM, 681000 SRAM and 74HC04 clock circuit. Its designer describes a modern 5 V DC supply and footprints for either a modulator or composite output. The project is presented as a way to repair a faulty ULA-based computer or modernize an existing machine while retaining an Issue 3-style board layout; do not treat its parts list as the ZX81+38 BOM. Read the replacement-board description.
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Check power, video and kit limitations before committing
- Power: Confirm the chosen project’s supply requirements, connector and polarity. The packaged kit page specifies a 110 V supply and says it did not offer UK/European supplies on that page, so that package detail cannot be assumed compatible with other regions. Kit details
- Video: Identify the output supported by the selected board and what display connection your setup requires. The CPLD replacement project specifies footprints for a modulator or composite output; that is not evidence that every recreation board provides both. Board description
- Keyboard and case: Check whether the design uses its own keyboard PCB and case files, and match those files to the motherboard revision before fabrication. ZX81+38 files and revision notes
- Packaged kit: A historical vendor page lists a UK keyboard, case, PCB, passive components, connectors, ICs, cables and assembly instructions. It says the kit was aimed at South America and notes the regional supply and manual limitations; this page does not establish present availability. Kit page
Use original documentation as historical reference, not a modern BOM
An assembly manual lists a Sinclair Logic IC, 2364 ROM, Z80A or D780C1 processor, and either two PD2114LC RAM chips or one MK4118, along with other components. That list describes historical assembly documentation; it should not be substituted for the current bill of materials of a 74-series clone or the distinct CPLD replacement board. ZX81 assembly manual component list.
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