ZX Spectrum Servicing Manual (Thorn EMI Datatech, 1984)
The ZX Spectrum Servicing Manual hosted here is the original loose-leaf service manual, prepared by Thorn (EMI) Datatech Ltd for Sinclair Research Ltd and dated March 1984, copyright Sinclair Research Ltd. 67 pages. It was OCR'd for the Sinclair community by Andy Dansby.
The wiki already hosts the re-typeset Revision 1.3 edition, which is more legible and includes both of Sinclair's later supplements. This edition is hosted alongside it because it carries two sections the re-typeset edition does not, and those sections are the source of a large amount of the field-service advice that circulates about this machine.
What it has that the other edition does not
[edit | edit source]Service Data
[edit | edit source]A short set of modification and adjustment notes:
- The earplug modification — a 330 Ω resistor between the signal and earth leads so the earplug can be left in place while saving.
- An explicit warning that inserting or removing a joystick or other interface, especially via a Kempston, with the machine switched on will damage the power resistors and the regulator.
- The voltage-generator modification — a 22 µF capacitor between TR4 and D15 where not already fitted, R60 changed to 270 Ω on early models, and C74 fitted if missing.
- The manufacturer's advised modifications for early versions, including replacing C46 with a high-temperature 1 µF part.
- Tape and sound circuit check: 5 V pk-pk at the ear socket for 2 V pk-pk at IC1 verifies IC1.
- Colour alignment for early boards — 130 mV at IC4 pin 4 via VR1, −75 mV at pin 2 via VR2, and TC2 set for a 4.433619 MHz subcarrier.
Repair Data, symptoms 1 to 14
[edit | edit source]A field-service symptom list added by T.I.S. (Technical Information Services), whose other repair manuals are advertised in the same volume. It is the origin of:
| # | Covers |
|---|---|
| 1 | General repair procedure — check the heatsink first on any reported fault, look for dry joints, cracked print and boards, badly fitted ICs and tarnished contacts; inspect add-ons; suspect a blown TR4 and/or destroyed RAM if a Kempston was used |
| 2 | Will not load from a recorder — azimuth adjustment, and the point that a recorder can play music perfectly and still be misaligned for a Spectrum |
| 3 | No coil buzz, −5 V absent — TR4, TR5 and the coil are not uncommonly all faulty together; and the ten-second wait before removing a bypass test RAM |
| 4 | Direct check for a single faulty RAM, with the POKE 85 / POKE 170 bit-to-IC table |
| 5 | No coil buzz, 7805 open circuit — check the heatsink and the print around its screws before replacing the regulator |
| 6 | Continual failure of power supply transistors |
| 7 | Keyboard faults — check the 5 V supply reaches the keyboard before replacing the ULA; the commonest cause of a wholly dead keyboard is a faulty 10 kΩ resistor in the R65–R69 group, identified by which column has failed |
| 8 | Faults which appear only when warm — heatsink first, then the ULA |
| 9 | Intermittent faults — check the board for hairline cracks and breaks, especially radiating from the heatsink screws |
| 10 | A Texas SN1889 fitted in the IC14 position instead of an LM1889, which should be replaced |
| 11 | Power supply good, computer not working correctly — the +5 V distribution order IC1, IC2, IC24, IC23, IC3, IC4, IC26, IC25, IC5; and sound as an indicator of the ULA |
| 12 | Making a permanent IC checker for logic-probe use |
| 13 | Flickering white background |
| 14 | Spare parts suppliers, as of the date of printing |
How to cite it
[edit | edit source]The Repair Data is not Sinclair's own text. It is T.I.S. field-service material bound into a Sinclair manual, and its opening claim — that "some 50% of new ones" were reportedly returned for replacement — is reported at second hand and is not a Sinclair figure. Cite the Repair Data as a third-party field-service source and the numbered sections 1 to 5 of the manual body as Sinclair's own.
One further caution: symptom 4 reproduces the RAM bit-to-IC table with "IC16 gives 158", where both this manual's own body text and the re-typeset edition give 168. Use 168.
Download it here: ZX Spectrum Servicing Manual Thorn EMI Datatech 1984.pdf
Related pages
[edit | edit source]- Sinclair ZX Spectrum Service Manual — the re-typeset Revision 1.3 edition, with both supplements
- Sinclair ZX Spectrum
- Sinclair ZX Spectrum+
- Sinclair ZX Spectrum+ Troubleshooting Guide
- Sinclair ZX Spectrum Troubleshooting Guide