RetroTechCollection

Sinclair ZX Spectrum Capacitor Replacement Guide

Replacing the electrolytic capacitors (“recapping”) in your Sinclair ZX Spectrum is a crucial maintenance step to ensure long-term reliability, stable video output, and protection against power-related failures. Aging capacitors are a common cause of instability, random resets, video artifacts, and audio noise.

Visual Inspection & Failure Signs

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  • Bulging or leaning capacitors – especially the large power filter (C9 on Issue 2/3 boards).
  • Leaking electrolyte – brown or green crust at the base of a capacitor.
  • Corrosion or PCB staining – green residue or darkened areas around caps.
  • Video or audio glitches – rolling picture, loss of sync, or buzzing audio may indicate dried-out decoupling capacitors.
  • Intermittent resets or boot failures – often caused by high-ESR or failed timing capacitors.

If any capacitor shows signs of failure, it is strongly recommended to replace all electrolytics on the board.

ZX Spectrum Capacitor Lists

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The original ZX Spectrum was produced in several board revisions (Issue 1–6A). Capacitor values are generally consistent, but always verify against your board’s silkscreen.

ZX Spectrum 16K/48K (Issue 2, 3, 4, 4A, 5, 6A)

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ZX Spectrum Mainboard Electrolytic Capacitors
Ref Capacitance Voltage Purpose / Rail
C1 1 µF 63 V Composite video coupling
C2 22 µF 16 V 5 V decoupling (ULA)
C3 1 µF 63 V EAR/MIC input coupling
C5 22 µF 16 V 5 V decoupling (CPU)
C6 1 µF 63 V EAR/MIC output coupling
C7 22 µF 16 V 5 V decoupling (RAM)
C8 22 µF 16 V 5 V decoupling (RAM)
C9 1000 µF 16 V Main 5 V power filter
C10 22 µF 16 V 5 V decoupling (ROM)
C11 22 µF 16 V 5 V decoupling (logic)
C12 22 µF 16 V 5 V decoupling (logic)
C27 1 µF 63 V MIC output coupling

Some early Issue 1 boards have minor differences; always check your board.

ZX Spectrum+ and 128K Models

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The ZX Spectrum+ uses the same mainboard as late 48K models, with identical capacitor values. The 128K “Toastrack” and +2 add a few extra capacitors for the sound circuit, DC-DC converter, and RAM.

ZX Spectrum 128K/+2 Additional Electrolytic Capacitors
Ref Capacitance Voltage Purpose
C46 470 µF 16 V DC-DC converter smoothing
C47 100 µF 16 V +12 V RAM supply
C48 22 µF 16 V +12 V RAM supply
C49 10 µF 16 V +12 V RAM supply
C50 1 µF 63 V Audio coupling
C51 1 µF 63 V Audio coupling
C52 1 µF 63 V Audio coupling

The +2A/+3 models use a different PCB and power supply; consult their specific service manuals for capacitor lists.

Recapping Procedure

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  1. Disassemble – Remove case screws, carefully separate keyboard membrane from mainboard.
  2. Label keyboard and speaker leads.
  3. Desolder capacitors – Use solder wick or a pump; avoid lifting PCB pads.
  4. Install new capacitors – Match polarity (long lead = +), and lead spacing (2.5 mm or 5 mm).
  5. Keep capacitor height ≤ 13 mm to clear the case.
  6. Clean flux residue with IPA and inspect for solder bridges.
  7. Reassemble and test – Power up with a known-good supply.

Post-Recap Voltage / Ripple Checks

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Expected Rails – BASIC prompt, no peripherals
Test Point Voltage (DC) Max Ripple (p-p)
Main 5 V (IC pin 14/28) 4.90 – 5.10 V < 50 mV
+12 V (128K RAM, if present) 11.5 – 12.5 V < 100 mV
-5 V (128K RAM, if present) -4.5 – -5.5 V < 100 mV

Excessive ripple can cause video instability or RAM errors.

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  • 40–60 W temperature-controlled soldering iron (fine tip)
  • Solder wick and/or desoldering pump
  • Leaded 63/37 or quality lead-free solder
  • 105 °C, low-ESR radial electrolytic capacitors (Nichicon, Panasonic, Rubycon)
  • Isopropyl alcohol (IPA) and antistatic brush
  • Kapton tape (to insulate capacitors near the modulator or case)

Extra Tips

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  • Check your power supply first! A faulty PSU can damage new capacitors and ICs.
  • Replace all electrolytics at once – partial recaps are not recommended.
  • Observe polarity! Electrolytic capacitors are polarized; incorrect fitting can cause failure.
  • Keep leads short and capacitors close to the PCB for best fit.
  • Clean up any electrolyte residue from old leaking capacitors to prevent corrosion.
  • If you have video mods (composite, S-Video), ensure you use quality capacitors in the video path (C1, C3, C6, C27).
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