Josh: Add the relevant circuit diagram already hosted here

2026-09-27T08:34:00Z

Add the relevant circuit diagram already hosted here

← Older revision		Revision as of 09:34, 27 September 2026
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	The copy hosted here is the re-typeset '''Revision 1.1''' edition prepared by Brendan Alford for the Spectrum For Everyone project. '''46 pages.'''		The copy hosted here is the re-typeset '''Revision 1.1''' edition prepared by Brendan Alford for the Spectrum For Everyone project. '''46 pages.'''

			[[File:Sinclair ZX Spectrum 128 circuit diagram (sheet 1).png\|thumb\|420px\|Sheet 1 of the three-sheet circuit diagram reproduced in this manual's appendices.]]
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Josh: New documentation page for the newly hosted ZX Spectrum 128 Service Manual: contents, what it settles, and the fact that its symptomatic-fault table was never completed

2026-09-27T08:21:07Z

New documentation page for the newly hosted ZX Spectrum 128 Service Manual: contents, what it settles, and the fact that its symptomatic-fault table was never completed

New page

The '''Sinclair ZX Spectrum 128 Service Manual''' is Sinclair Research's official service documentation for the [[Sinclair ZX Spectrum 128|ZX Spectrum 128]] "Toastrack". Like the [[Sinclair ZX Spectrum Service Manual]] and the [[Sinclair QL Service Manual]] it is written at full component level, so '''every capacitor, resistor, diode, transistor and IC on the main PCB and on the numeric keypad PCB is documented by designator, value, rating and manufacturer'''.

That makes it the primary reference for [[Sinclair ZX Spectrum 128 Capacitor Replacement Guide]], [[Sinclair ZX Spectrum 128 General Maintenance]] and [[Sinclair ZX Spectrum 128 Troubleshooting Guide]], and — because Amstrad published no service manual for the grey [[Sinclair ZX Spectrum +2|+2]], which is a repackaged 128 — the closest official documentation for that machine too.

The copy hosted here is the re-typeset '''Revision 1.1''' edition prepared by Brendan Alford for the Spectrum For Everyone project. '''46 pages.'''

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== Contents ==

{| class="wikitable styled-table" style="width:85%; text-align:left;"
! Section !! Covers
|-
| Section 1 || System description — Z80A CPU, memory organisation and bus arbitration, I/O, TV picture generation and sound, keyboard scanning, tape interface, the AY-3-8912A programmable sound generator, the RS232/MIDI interface, keypad scanning with its reset and bit-transfer protocols, and the on-board power supplies
|-
| Section 2 || Disassembly and assembly
|-
| Section 3 || Setting up instructions and system test
|-
| Section 4 || Fault finding and repair — test equipment, diagnosis technique, power supply unit, the initialisation check sequence, and repair notes
|-
| Section 5 || Parts lists — notes to Table 5.4, case assembly (Table 5.3), '''main PCB components (Table 5.4)''', '''keypad PCB components (Table 5.5)''' and part-number references
|-
| Section 6 || Appendices — PCB rear foil layout, digital schematics, analogue schematics and the block diagram
|}

== What it settles ==

* '''The complete main-board capacitor list''', including which of the C1–C130 positions are unpopulated. Thirteen electrolytics; everything else is ceramic.
* '''The rails and what each one feeds.''' +5 V from a 7805 for all logic, the ULA and the sound/UHF modulators; +12 V from the TR4/TR5 inverter (rectified and smoothed by D15/C44) for the RS232 driver IC33 and the keypad; −12 V from the C111/C112 charge pump with D28/D29 for the same driver; and −5 V from that rail through zener D19 for the expansion port.
* '''The basic-check test points''': +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, −5 V at the D19 anode.
* '''The clock frequencies''': 17.73447 MHz at IC37 pin 6, 3.54689 MHz at IC2 pin 6, 8.8 MHz at IC1 pins 46 and 47, all specified with no jitter.
* '''The RAM specification''': 4164, 150 ns access time, 128-row refresh, with ten acceptable manufacturers named.
* '''The external supply specification''': at 215 V AC mains and 1.4 A the trough must not fall below 7.0 V; at 265 V AC and 600 mA the peak must stay below 13 V.

== What it does not contain ==

'''Section 4.2.4, "Symptomatic Faults", is empty.''' The table is printed as "TBD" with an author's note that the details would follow once production and in-service history were known — and they never were. There is therefore '''no manufacturer symptom-to-cause table for the 128''', which is why this wiki's 128 troubleshooting guide draws its symptom tables from the 48K manual's equivalent section and from community repair experience.

It also carries no service history for the [[Sinclair ZX Spectrum +2|+2]] or the +2A/+3, and no Datacorder information.

<pdf> File:ZX Spectrum 128 Service Manual.pdf </pdf>

Download it here: [[:File:ZX Spectrum 128 Service Manual.pdf|ZX Spectrum 128 Service Manual.pdf]]

== Related pages ==

* [[Sinclair ZX Spectrum 128]]
* [[Sinclair ZX Spectrum 128 Capacitor Replacement Guide]]
* [[Sinclair ZX Spectrum 128 General Maintenance]]
* [[Sinclair ZX Spectrum 128 Troubleshooting Guide]]
* [[Sinclair ZX Spectrum +2]]
* [[Sinclair ZX Spectrum Service Manual]]

[[Category:Sinclair Computers]]
[[Category:Service Manuals]]

Sinclair ZX Spectrum 128 Service Manual - Revision history

Josh: Add the relevant circuit diagram already hosted here

Josh: New documentation page for the newly hosted ZX Spectrum 128 Service Manual: contents, what it settles, and the fact that its symptomatic-fault table was never completed