Editing Sinclair ZX Spectrum Capacitor Replacement Guide

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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) ===
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''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 ===
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.

{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''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 ==
# '''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 ==
{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''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.''

== 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).

== Related Pages ==
* [[Sinclair ZX Spectrum Troubleshooting Guide]]
* [[Sinclair ZX Spectrum Power Supply Repair]]
* [[Sinclair ZX Spectrum Composite Video Mod]]
[[Category:Sinclair Computers]]
[[Category:Capacitor Replacement Guides]]