Sinclair ZX Spectrum +2 Capacitor Replacement Guide

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 +3-family Z70830/Z70833 boards with a completely different power architecture.

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.

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. 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.
• 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.

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:

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 a dead RS-232 port rather than the 48K machine's white screen — the video, sound and UHF modulators run from +5 V), 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.

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 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

1. Unplug the power, remove the six case screws and separate the halves, disconnecting the keyboard ribbons and tape deck connector.
2. Lift the board out so it is supported flat.
3. Record value, voltage and polarity for every electrolytic before removing it.
4. Add fresh flux and solder to both joints and let it mix with the old solder.
5. Lift one lead at a time with the joint fully molten; clear the hole with wick.
6. Fit the replacement the correct way round; solder and trim.
7. 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

1. 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.
2. Confirm the 128 menu appears.
3. Check the rails: +5 V, +12 V, −12 V and −5 V.
4. Verify the clocks are clean and jitter-free: 17.73447 MHz at IC37 pin 6 and 3.54689 MHz at IC2 pin 6.
5. 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