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ZX Spectrum Servicing Manual (Thorn EMI Datatech, 1984)

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The ZX Spectrum Servicing Manual is Sinclair Research's service manual for the 16K and 48K Sinclair ZX Spectrum, "prepared by Thorn (EMI) Datatech Ltd for Sinclair Research Ltd", dated March 1984. It is written for authorised dealers and engineers and covers the Issue 2 and Issue 3 boards, with the Issue 1 board in its modification history. The hosted copy has a supplement by T.I.S. (Technical Information Services) bound at the end: General Data, Service Data and a fourteen-item Repair Data list.

The hosted file

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The PDF (67 pages) is not a facsimile. It was made in 2002 by Andy Dansby with ABBYY FineReader OCR: the text pages are the OCR output set in ordinary fonts, and only the figures, circuit diagrams and board layouts are scanned images, at 150 dpi black and white. The first page carries Dansby's credit and a statement that the content is Amstrad's property.

OCR errors are present in the text. Spaced-out letters ("f a u l t s") are cosmetic, but some digits and symbols are wrong:

  • Repair Data symptom 4 prints the RAM test result as "32767 or 85535" and the IC16 code as "158". Sinclair's own memory check in section 4 (pp. 4.8–4.9) of the same file gives 65535 for a 48K machine and 168 for IC16. Use 65535 and 168.
  • µ is read as "W", "y" or "u" in the parts lists (C74 appears as "4.7WF", C65 as "lOOyF"), and "lO" stands for 10 throughout.
  • Section 1, paragraph 3.2 has the data bus as "D7-D10" (D7–D0).

Check any figure taken from the text against the scanned figure pages or another edition before relying on it.

Contents

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Contents of the hosted PDF
PDF pages Printed pages Content
1 – OCR credit
2–4 (i) Title, list of contents and illustrations, "Prepared by Thorn (EMI) Datatech Ltd for Sinclair Research Ltd, March 1984"; introduction; safety measures
5–21 1.1–1.10 Section 1, System description: architecture, Z80A, memory organisation, input/output, power supplies (paragraphs 6.1–6.3). Fig. 1.1 block diagram (PDF p. 7), Fig. 1.4 Issue 2 circuit diagram (pp. 9–11), Fig. 1.5 Issue 3 circuit diagram (pp. 12–14), Fig. 1.2 expansion RAM timing (p. 17)
22–23 2.1–2.2 Section 2, Disassembly and assembly
24–26 3.1–3.3 Section 3, Setting up and system test: voltage check, colour adjustment (VR1, VR2 at IC14), sub-carrier and 14 MHz oscillators, system test
27–48 4.1–4.22 Section 4, Fault diagnosis and repair: test equipment, modification history (Issue 1, Issue 2 and Issue 3B changes), 32K extension memory, Hitachi and NEC ROMs, power supply unit (p. 4.7), initialisation, memory check (pp. 4.8–4.9), keyboard structure (p. 4.10), fault-finding guide (pp. 4.11–4.16), Fig. 4.2 speaker load waveforms, Table 4.1 IC14 (LM1889) pin signals, repair, 16K to 48K upgrade, Fig. 4.3 expansion memory IC locations, Fig. 4.4 Issue 3 RAM links
49–56 5.1–5.6 Section 5, Parts lists: notes to Table 5.2, Table 5.1 case assembly, Table 5.2 board assembly in Issue 2, Issue 2 modified and Issue 3 columns. Fig. 5.1 Issue 2 layout (PDF p. 49), Fig. 5.2 Issue 3 layout (p. 52)
57 – T.I.S. General Data: case versions, dismantling, edge connector, RAM links
58 – List of other T.I.S. manuals
59 3 T.I.S. Service Data
60–66 4 onwards T.I.S. Repair Data, symptoms 1 to 14, with a generalised circuit diagram and early and later board layouts (pp. 61–63)
67 – Blank notes page

Figures that differ between editions

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The re-typeset Revision 1.3 edition hosted as Sinclair ZX Spectrum Service Manual differs from this one in at least two values:

  • Power supply (section 4, paragraph 2.2, p. 4.7). This edition: at 215 V AC input and 1.4 A output the trough must not fall below 7.0 V; at 265 V AC and 600 mA the peak must be less than 13 V. The re-typeset edition gives 14 V.
  • C74 on modified Issue 2 boards. This edition gives a 4.7 µF electrolytic in both the modification history (section 4, paragraph 1.3(h), p. 4.4: R60 changed from 100 Ω to 270 Ω and a 4.7 µF electrolytic fitted between TR5 emitter and base) and Table 5.2 (4.7 µF, 5 V minimum; note 3 makes C74 essential on all Issue 2 boards). The re-typeset edition's parts list prints 47 µF.

The T.I.S. supplement

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The supplement is not Sinclair's text. Repair Data symptom 1 opens with the claim that "some 50% of new ones" were "alleged" to have been returned for replacement, which T.I.S. itself reports at second hand. The Service Data page (PDF p. 59) gives:

  • a 330 Ω resistor across the earplug lead so that it can stay connected while saving;
  • a warning that plugging or unplugging joysticks or interfaces, especially a Kempston, with the power on damages the power resistors and the regulator;
  • the voltage-generator modification: a 22 µF capacitor between TR4 and D15 where not fitted, R60 changed to 270 Ω on early models, and C74 fitted if missing;
  • for early boards, axial capacitors in place of the ceramics and a high-temperature 1 µF part at C46;
  • a tape and sound check: 5 V peak to peak at the EAR socket should give 2 V peak to peak at IC1;
  • colour alignment for early boards: 130 mV at pin 4 via VR1 and −75 mV at pin 2 via VR2 (the text says IC4; Sinclair's section 3 uses IC14, the LM1889), and TC2 set for a 4.433619 MHz sub-carrier.
T.I.S. Repair Data symptoms
No. Heading and main points
1 General repair procedure: check the heatsink first, then for dry joints, cracked print, badly fitted ICs and tarnished contacts; check add-ons; suspect TR4 and the RAMs if a Kempston interface has been used
2 Will not load from a recorder: adjust the recorder's head azimuth
3 No inverter buzz, −5 V absent: replace TR4 (ZTX650), but check TR5 (ZTX213) and the coil, which can fail with it; check for damaged RAMs; wait about ten seconds after switch-off before removing a substitute RAM
4 Direct check for a single faulty RAM, using POKE 85 and POKE 170 (see the OCR note above)
5 No inverter buzz, 7805 open circuit: check the heatsink and the print around its screws first
6 Continual failure of the power supply transistors
7 Keyboard faults: check +5 V reaches the keyboard before changing the ULA; names a faulty 10 kΩ resistor (R65 to R69), identified by which column has failed, as probably the commonest fault
8 Faults only when warm: heatsink, then IC1 (ULA)
9 Intermittent faults: holders, dry joints, and hairline cracks in the board, especially around the heatsink screws
10 A Texas SN1889 fitted instead of an LM1889: replace it
11 Supply good but computer faulty: check +5 V reaches IC1, 2, 24, 23, 3, 4, 26, 25 and 5 in that order; missing sound points at IC1
12 Making a reference table of logic probe readings from a good machine
13 Flickering white background
14 Spare parts suppliers at the time of printing

What it does not contain

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  • Fig. 5.3, the Issue 3B component layout, is listed among the illustrations but is not in the file.
  • No Issue 4, 5 or 6 boards and no Spectrum+. Sinclair's supplements for those are in the re-typeset edition at Sinclair ZX Spectrum Service Manual.
  • No 128K machine; see Sinclair ZX Spectrum 128 Service Manual.
  • No facsimile of the text pages, so typography and OCR errors cannot be checked against the original within this file.
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Fig. 1.4 (Issue 2) and Fig. 1.5 (Issue 3) in this file are 150 dpi scans. Larger prints of the same boards are in the Ferranti Archives 2026: Sinclair's Issue Two circuit diagram (SRC 102, 16 August 1982) and Timex's Issue 3 drawing (drawing 356-201891-02, June 1983). The Timex drawing shows the expansion RAM select links, marked H, L, 3, 4, TI and OKI, that the T.I.S. General Data page lists.

Pages that cite this document

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Download: ZX Spectrum Servicing Manual Thorn EMI Datatech 1984.pdf

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