Editing Sinclair ZX Spectrum +2 Capacitor Replacement Guide

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[[File:Sinclair ZX Spectrum 128 circuit diagram (sheet 1).png|thumb|420px|ZX Spectrum 128 circuit diagram, sheet 1. The grey +2 is functionally a repackaged 128, so these diagrams describe its power and audio circuitry.]]

This guide covers the capacitors on the grey '''[[Sinclair ZX Spectrum +2]]''' (boards Z70500 Issue 3 and Z70700 Issue 1). It does '''not''' apply to the black +2A/+2B, which use the [[Sinclair ZX Spectrum +3|+3]]-family Z70830/Z70833 boards with a completely different power architecture.<ref name="sfe">[https://www.spectrumforeveryone.com/technical/zx-spectrum-models/ "ZX Spectrum Models"], Spectrum for Everyone. Source for the two grey +2 board revisions, the axial-capacitor note on the Z70700, the poor PCB quality warning, and the +2A/+3 differences including deletion of the DC-DC converter.</ref>

== ⚠️ Safety and board handling ==

There are '''no mains voltages inside the computer''' — it runs from an external supply and the highest rail on the board is +12 V, so capacitor work here is low voltage.<ref name="sm128">''ZX Spectrum 128 Service Manual'', Sinclair Research Ltd. Source for the on-board power supply description (7805, TR4/TR5 inverter, D15/C44, charge pump C111/C112 with D28/D29, zener D19), the rails and their loads, the supply tolerances and the repair notes.</ref>

The hazard is to the board. '''The Amstrad-built PCB is of notably poor quality and its pads and tracks lift easily''' — this is the single biggest risk in recapping a +2.<ref name="sfe" /> Follow the soldering rules in the [[Sinclair ZX Spectrum +2 General Maintenance]] guide: temperature-controlled iron, fresh flux and solder onto every old joint before removal, short dwell times, no flexing, and a careful inspection for splatter afterwards.

== Is the +2 a recap candidate? ==

The +2 has ordinary leaded electrolytics and is '''not''' a machine with a systematic capacitor plague. Given the fragile board, a blanket recap does more harm than good — '''replace on evidence, not on principle'''.

Recap where it is justified:

* '''Visibly failed parts''' — bulging, leaking, crusty residue or a cracked sleeve.
* '''Supply instability''' — random crashes, or rails that measure out of tolerance or show ripple.
* '''Audio hum''' — but check the grounding first. On Taiwanese-built +2s a constant hum is usually the tape PCB's grounding through the mechanism frame, cured by tightening the two screws holding the PCB to the mechanism. Do that before replacing any audio capacitors.<ref name="sfe2">Spectrum for Everyone, [https://www.spectrumforeveryone.co.uk/technical/servicing-2s-datacorder/ "Servicing your +2's Datacorder"]. Source for the grounding-related audio hum and its fix.</ref>
* '''Datacorder problems''' — almost always the drive belt and head, not capacitors. Service the mechanism first.

A useful capacitor test carried over from the 48K machines: if the display shows '''wavy lines''', press down on each electrolytic in turn — if the lines clear while you press one, that is the faulty part.<ref name="sm48">''ZX Spectrum Service Manual'' (48K), Sinclair Research Ltd — fault-finding guide.</ref>

== Where the capacitors matter ==

Amstrad did not publish a service manual for the grey +2, so there is no official per-designator parts list for these boards. What ''is'' documented is the '''power supply circuit''', which the +2 inherits from the Spectrum 128, and that identifies the capacitors that actually matter:<ref name="sm128" />

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Key capacitors in the +2 / 128 power circuit'''
! Reference !! Role
|-
| '''C44''' || With D15, rectifies and smooths the square wave from the TR4 collector and the inverter coil to produce the '''+12 V''' rail
|-
| '''C111 / C112''' || The '''charge pump''' which, with D28 and D29, derives the '''−12 V''' rail from the same square wave. The −5 V rail is then taken from −12 V via zener D19
|-
| Regulator input / output capacitors || Around the '''7805''' producing the +5 V logic rail
|}

These are the parts to check first if the ±12 V rails are wrong (which on a +2 shows up as video or RS232 faults rather than the 48K machine's white screen), or if the +5 V rail is rippling.

'''Board difference worth knowing:''' the UK-built '''Z70700 Issue 1''' uses '''mostly axial capacitors''' and other UK-sourced parts, whereas the Taiwanese '''Z70500 Issue 3''' uses a different component set. Check which board you have before ordering — the physical form factor differs even where the values match.<ref name="sfe" />

== Reading the values off your board ==

Because no published +2 parts list exists, the correct procedure is to '''read each capacitor's value, voltage and polarity directly off the fitted part''' and record it before removal. The [[Sinclair ZX Spectrum +2#Circuit diagrams|128 circuit diagrams]] hosted on this wiki show the circuit positions and can be used to confirm what each capacitor does.

This guide deliberately does not reproduce a per-designator table for the +2 rather than risk publishing values that were never officially documented for these boards. Where a value is legible on the part or the silkscreen, that is the authority.

== Choosing replacements ==

* '''105 °C''' aluminium electrolytics, equal capacitance, equal-or-higher voltage.
* Match the '''form factor''' to the board — axial on the Z70700, radial where radial was fitted.
* Low-ESR parts are appropriate for the supply rails; ordinary grades are fine elsewhere.
* Do not substitute for the small ceramic and film capacitors; they are stable and rarely fail.

== Replacement procedure ==

# Unplug the power, remove the six case screws and separate the halves, disconnecting the keyboard ribbons and tape deck connector.
# Lift the board out so it is supported flat.
# '''Record value, voltage and polarity for every electrolytic before removing it.'''
# Add fresh flux and solder to both joints and let it mix with the old solder.
# Lift one lead at a time with the joint fully molten; clear the hole with wick.
# Fit the replacement the correct way round; solder and trim.
# Given the board's fragility, '''inspect every pad under magnification''' for lifting or ring cracks before reassembly, and repair any broken track with an insulated wire link.

== Post-recap verification ==

# Power up on a '''current-limited supply''' set to about 1.5 A. A healthy +2 draws roughly 800 mA–1.2 A; immediate current limiting means a short, not a capacitor problem.<ref name="tyne">Tynemouth Software, [http://blog.tynemouthsoftware.co.uk/2017/06/spectrum-128k-2-grey-repairs.html "Spectrum 128K +2 Grey Repairs"]. Source for typical current draw and diagnostic practice.</ref>
# Confirm the 128 menu appears.
# Check the rails: +5 V, +12 V, −12 V and −5 V.
# Verify the clocks are clean and jitter-free: 17.73447 MHz at IC37 pin 6 and 3.54689 MHz at IC2 pin 6.<ref name="sm128" />
# Test AY sound and the beeper, a tape load and save, both joystick ports and the full keyboard.

If a previously-working function fails after the recap, check the polarity of every replaced electrolytic first.

== Related pages ==

* [[Sinclair ZX Spectrum +2]]
* [[Sinclair ZX Spectrum +2 General Maintenance]]
* [[Sinclair ZX Spectrum +2 Troubleshooting Guide]]
* [[Sinclair ZX Spectrum+ Capacitor Replacement Guide]] — the 48K machine, which does have a published parts list
* [[Sinclair ZX Spectrum Capacitor Replacement Guide]]
* [[Capacitor Failure Symptoms]]

== References ==

<references />

[[Category:Sinclair Computers]]
[[Category:Capacitor Replacement Guides]]