Sinclair ZX Spectrum 128 Service Manual
The Sinclair ZX Spectrum 128 Service Manual is Sinclair Research's service manual for the ZX Spectrum 128 "toastrack". The copy hosted here is Revision 1.1 of a re-typeset edition edited by Brendan Alford for the Spectrum For Everyone website, 46 pages. It covers the 128's main board and its numeric keypad at component level, with a parts list giving the designator, value and rating or type of every capacitor, resistor, diode, transistor and IC.
Contents
[edit | edit source]| Section | Title | Page |
|---|---|---|
| 1 | System description: architecture, Z80A CPU, memory organisation and bus arbitration, input/output (TV picture and sound, keyboard scanning), tape interface, programmable sound generator, RS232/MIDI interface, keypad scanning, power supplies (1.10) | 4–21 |
| 2 | Disassembly/assembly | 22–23 |
| 3 | Setting up and system test | 24 |
| 4 | Fault finding and repair: test equipment (4.1.1), fault diagnosis techniques, power supply unit, initialisation and basic checks (4.2.1–4.2.3), symptomatic faults (4.2.4), repair (4.3) | 25–32 |
| 5 | Parts list: notes to Table 5.4 (5.2), case assembly (5.3), main PCB components (Table 5.4), keypad PCB components (Table 5.5), part number references (5.6) | 33–42 |
| 6 | Appendices: PCB rear foil layout, digital schematics, analogue schematics, block diagram | 43–46 |
What it contains
[edit | edit source]- The main-board capacitor list (Table 5.4, pp. 35–39), including which of the positions C1–C130 are not used. Thirteen of the fitted capacitors are electrolytics; the rest are ceramics. Table 5.4 does not say which board version it describes. Spectrum for Everyone's community list has the same thirteen for the Spanish Version 2 and 2-1 boards and a fourteenth, C131 (47 µF), on the UK Version 6K, 6U and 9G boards.[1]
- The supply rails and their loads (section 1.10, p. 20): +5 V from a 7805 for the logic, the ULA and the sound and UHF modulators; +12 V from the TR4/TR5 inverter, rectified by D15 and smoothed by C44, for the RS-232 driver IC33 and the keypad; −12 V from the charge pump C111, C112, D28 and D29 for IC33; and −5 V from that rail through zener D19 for the expansion port.
- The basic-check table (section 4.2.3, p. 28): +9 V ±2.0 V at the positive side of C50, +5 V ±0.25 V at C34 and IC15 pin 8, +12 V ±0.5 V at IC33 pin 14, −12 V at IC34 pin 1 and −5 V at the D19 anode; and the clocks, 17.73447 MHz at IC37 pin 6, 3.54689 MHz at IC2 pin 6 and 8.8 MHz at IC1 pins 46 and 47, all with no jitter.
- The RAM specification (section 5.2, note 1): 4164, 150 ns access time, 128-row refresh, with ten approved makers.
- The external power pack specification (section 4.2.2, p. 27): with 215 V AC mains and a 1.4 A load the trough must not fall below 7.0 V; with 265 V AC and 600 mA the peak must stay below 13 V.
- The disassembly and keyboard reassembly procedure (section 2, pp. 22–23) and the spare part numbers (section 5.6), including the 9 V 1.85 A power supply UK1850 (X-1220).
What it does not contain
[edit | edit source]Section 3, "Setting Up and System Test", is printed as "TBD", so there is no alignment procedure for the sound carrier. Section 4.2.4, "Symptomatic Faults", is also printed as "TBD", with an author's note that the table would follow when production and in-service history were known. Sinclair therefore published no symptom-to-cause table for the 128. The PCB component layout drawings referred to as figures 5.1 and 5.2 are marked by the editor as missing from the available documentation.
The manual does not cover the grey +2 or its Datacorder. Amstrad issued its own 12-page Spectrum +2 Service Manual for that machine, with an electrical parts list, circuit diagram, PCB layouts and the cassette mechanism; it is hosted as File:Amstrad Spectrum +2 Service Manual.pdf. The +2A, +2B and +3 are not covered by either.
Original circuit drawings in the Ferranti Archives
[edit | edit source]Ferranti's file on the 128's ULA, now part of the Ferranti Archives 2026, contains Sinclair's own circuit drawings for the 128 and the production redraws made by Timex in Dundee. They are clearer than the low-resolution schematics in this manual's appendices.[2][3][4][5]
| Drawing | Dates and issues | Contents |
|---|---|---|
| Sinclair analogue circuit (SPEC128-SIN-SCH-021) | Dated 24 May 1985; issue 2, 1 November 1985 | The 17.7345 MHz oscillator (X1, IC37 74S04), the TEA2000 colour encoder (IC36), the RGB socket drive, the composite video buffer, the UM1233 modulator, and the MC1376 (IC38) that puts the ULA and AY sound onto the TV signal as an FM carrier |
| Sinclair logic circuit (SPEC128-SIN-SCH-023) | Dated 23 July 1985; mod 1, 27 August (D32 and R138 among the parts added); mod 2, 3 September (C129 added); mod 3, 7 November 1985 (TR13, TR15, R139 to R143, R145, R146 and C132 added) | The Z80A, ROM, the ULA (labelled "7C ULA"), both banks of 4164 RAM, the ZX8401, the 10H8 paging PAL, the 74LS174 bank register, the AY-3-8912A, the 1488 and 1489, the 7805 supply, the +12 V converter and the negative rails. Its notes say that the address connections to the edge connector are "all as in the Spectrum 6A" and that the 5 V regulator is connected "as in the QL" |
| Timex logic circuit (SPEC128-TMX-SCH-026) | Issue 01, 17 February 1986; 02, 27 February ("IC27 mod"); 03, 5 March 1986 (keyboard and membrane connections for GRAPH, CAPS LOCK and "."; IC34 pin 4, was pin 9; R123 180 Ω, was 100 Ω). Stamped "PROVISIONAL" | A hand-lettered redraw of the Sinclair logic sheet, with an edge-connector pin table, a table of membrane connections for each key, and transistor lead views. R73 and C129 are circled and marked "removed" in another hand. The bottom edge of the scan cuts off the drawing number and the last rows of the tables |
| Timex analog circuit (SPEC128-TMX-SCH-027) | Drawing 375-281001; issue 01, 21 February 1986; 02, 5 March 1986 (R101 and R102 180 Ω, were 820 Ω; IC36 pin 18, was pin 8; note added). Stamped "PROVISIONAL" | A redraw of the Sinclair analogue sheet, with pin diagrams of the TOKO coils, transistor lead views, front and solder-side views of the RGB socket, and a note giving C120 and C124 for Kony and C.S.I. crystals |
The edge-connector side letters given in brackets on the Timex logic circuit do not agree with the side headings of its own pin table, so check against a board before relying on either.[4] The same file holds the data pages kept for two of the 128's analogue ICs: an application circuit for the MC1376 from a D.A.T.A. book (SPEC128-EXT-DAT-024) and a distributor's catalogue page on the TEA1002 and TEA2000 encoders (SPEC128-EXT-DAT-025). Ferranti's own documents on the ULA are described on the Sinclair ZX Spectrum 128 ULA page.
Where the drawings differ from this manual
[edit | edit source]| Item | This manual (Table 5.4) | Archive drawings |
|---|---|---|
| R101, R102 (oscillator) | 820 Ω | 820 Ω on the Sinclair drawing; 180 Ω on Timex's issue 02[2][5] |
| C120, C124 (oscillator) | 100 pF and 20 pF | Timex: 150 pF and 20 pF for a Kony crystal; 10 nF and 22 pF for a C.S.I. crystal[5] |
| AY mixer and RGB vertical sync (TR15, R139 to R143, R145, R146, C132) | Not listed (the table stops at R138 and C130, and lists TR13 as a BC239B) | Added at Sinclair's mod 3, 7 November 1985[3] |
| R132 (AY sound to the MC1376) | 39 kΩ | 18 kΩ on both analogue drawings[2][5] |
| C103 (CAS delay, upper RAM) | Not used | 25 pF on both logic drawings[3][4] |
| C131 | Not listed | 47 µF 16 V on both analogue drawings[2][5] |
| R73, C129 (CPU clock) | Listed (1 kΩ, 100 pF) | On the Sinclair drawing; circled and marked "removed" on Timex's print[3][4] |
| IC1 | "7C001" (Ferranti) | "7C ULA" on the Sinclair drawing; Ferranti's type 7K010[3] |
The capacitor differences are set out in the Sinclair ZX Spectrum 128 Capacitor Replacement Guide.
Pages that cite this document
[edit | edit source]- Sinclair ZX Spectrum 128
- Sinclair ZX Spectrum 128 General Maintenance: disassembly, keyboard, rails, power pack and RAM specification
- Sinclair ZX Spectrum 128 Troubleshooting Guide: basic checks, rails and clocks
- Sinclair ZX Spectrum 128 Capacitor Replacement Guide: Tables 5.4 and 5.5
- Sinclair ZX Spectrum +2, Sinclair ZX Spectrum +2 Troubleshooting Guide and Sinclair ZX Spectrum +2 Capacitor Replacement Guide: the shared 128 architecture
Download: ZX Spectrum 128 Service Manual.pdf
Related pages
[edit | edit source]- Sinclair ZX Spectrum Service Manual, for the 16K, 48K and Spectrum+
- ZX Spectrum Servicing Manual (Thorn EMI Datatech, 1984)
- Sinclair ZX Spectrum 128 ULA, the Ferranti 7K010
- Ferranti Archives 2026
References
[edit | edit source]- ↑ "Capacitor Lists (128K Range)", Spectrum for Everyone (accessed 2026-10-16). Community list of electrolytics: the "Version 6K/Version 6U/Version 9G (UK 128K)" list adds C131 47 µF 10 V to the thirteen positions on the "Version 2/Version 2-1 (Spanish 128K)" list.
- ↑ 2.0 2.1 2.2 2.3 Sinclair Research, Spectrum 128 analogue circuit, drawing dated 24 May 1985, issue 2 of 1 November 1985, dyeline print, Ferranti Archives 2026 (SPEC128-SIN-SCH-021).
- ↑ 3.0 3.1 3.2 3.3 3.4 Sinclair Research, Spectrum 128 logic circuit, drawing dated 23 July 1985, mods 1 to 3 (27 August, 3 September and 7 November 1985), dyeline print, Ferranti Archives 2026 (SPEC128-SIN-SCH-023). Source for the mod 2 and mod 3 parts, the notes on the edge connector and regulator, and the "7C ULA" label.
- ↑ 4.0 4.1 4.2 4.3 Timex Corporation, Dundee, Spectrum 128 logic circuit, drawing 375-28100? (last digit cut off), issues 01 (17 February 1986), 02 (27 February 1986) and 03 (5 March 1986), stamped "PROVISIONAL", photocopy, Ferranti Archives 2026 (SPEC128-TMX-SCH-026). Source for the issue descriptions, the R73 and C129 "removed" marks, and the edge-connector, membrane and transistor tables.
- ↑ 5.0 5.1 5.2 5.3 5.4 Timex Corporation, Dundee, Spectrum 128 analog circuit, drawing 375-281001, issues 01 (21 February 1986) and 02 (5 March 1986), stamped "PROVISIONAL", photocopy, Ferranti Archives 2026 (SPEC128-TMX-SCH-027). Source for the issue 02 changes and the crystal note.