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File:Sinclair ZX Spectrum Issue 3 circuit diagram.png

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Description Sinclair ZX Spectrum Issue 3 main board circuit diagram. This is the board the body of the Sinclair ZX Spectrum Service Manual describes. It shows the PWR socket feeding C50 (22 uF) and the 7805 with C34 (22 uF) on its output; the TR4/TR5 inverter with its toroidal coil; D15 (BA157) and C44 (100 uF) producing +12 V for the 4116 RAM, with R62 and C45 giving the quieter +12VA rail for the colour circuits; and the C46 / D11 / R55 / D16 (5V1) / D12 / C47 chain that produces -5 V. It also carries Sinclair's own edge-connector pinout table and the note that the Issue 3B board changes R60 to 270R, C49 to 560 pF and adds C77.
Source Sinclair Research Ltd; mirrored in the Sinclair ZX Computers Archive at k1.spdns.de.
Date
Author Sinclair Research Ltd
Licence Used for archival / educational purposes with attribution.

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current17:28, 22 September 2026Thumbnail for version as of 17:28, 22 September 20264,055 ร— 2,781 (870 KB)Josh (talk | contribs)Sinclair ZX Spectrum Issue 3 circuit diagram