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
- 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
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)
| 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
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.
| 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
- Disassemble – Remove case screws, carefully separate keyboard membrane from mainboard.
- Label keyboard and speaker leads.
- Desolder capacitors – Use solder wick or a pump; avoid lifting PCB pads.
- Install new capacitors – Match polarity (long lead = +), and lead spacing (2.5 mm or 5 mm).
- Keep capacitor height ≤ 13 mm to clear the case.
- Clean flux residue with IPA and inspect for solder bridges.
- Reassemble and test – Power up with a known-good supply.
⚙️ Post-Recap Voltage / Ripple Checks
| 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.
🧰 Recommended Tools & Parts
- 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
- 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).