Sinclair ZX Spectrum+ Capacitor Replacement Guide

The 48K Spectrum circuit diagram from the Service Manual. The Spectrum+ uses the same board, so every capacitor designator below can be located on it.

This guide covers the capacitors on the Sinclair ZX Spectrum+. The Spectrum+ uses the standard 48K Spectrum board, so the values below — taken from the Service Manual parts list — apply to both.

⚠️ Safety and board handling

There are no mains voltages inside the computer; it runs from an external 9 V supply and the highest rail on the board is +12 V. Board-level capacitor work is therefore low voltage.

The board still needs care. Use recognised desoldering technique and an earthed, low-power iron; add fresh flux and solder to old joints before removing anything, keep dwell times short, and inspect for solder splatter afterwards — the manual warns that hairline bridges can measure several ohms and cause very misleading faults.

Pay particular attention to the area around the heatsink screws, where hairline cracks in the board are a documented cause of intermittent faults.

Is the Spectrum+ a recap candidate?

The Spectrum has ordinary leaded electrolytics and is not a machine with a systematic capacitor-failure problem. It is not a "recap on sight" machine.

That said, capacitors do cause real, documented symptoms here, and there is a neat diagnostic for it: if the screen shows wavy lines, press down on each electrolytic capacitor in turn — if the lines disappear while you press one, that capacitor is the fault.

Worthwhile targets:

• C50 (regulator input) and C34 (regulator output) — these are the Service Manual's supply test points, so out-of-tolerance or rippling rails point straight at them.
• C44 (100 µF, near IC6) — sits in the DC-DC converter area feeding the lower RAM.
• C46 — Sinclair specified this be replaced with a high-temperature type as a service modification.
• Any electrolytic that is bulging, leaking, or that changes the symptom when pressed.

Main board capacitor list

From Table 5 of the Service Manual. The manual tabulates Issue 2 and Issue 3 values; the Spectrum+ boards (Issue 4A/4B/4S/5/6A) carry these values forward with the differences noted. Unless otherwise stated all capacitors are axial types.

ZX Spectrum 48K / Spectrum+ main board capacitors

Ref	Value	Rating / tolerance	Type
C1–C8	47 nF	25 V, 10%	Ceramic
C25	22 µF	10 V, −10% +80%	Electrolytic
C26	47 nF	25 V, 10%	Ceramic
C27	1 µF	50 V, −10%	Ceramic
C28	22 µF	10 V, −10% +80%	Electrolytic
C29, C30	47 nF	25 V, 10%	Ceramic
C31, C32	100 nF	25 V, 10%	Ceramic
C33	47 nF	25 V, 10%	Ceramic
C34	22 µF	10 V, −10% +80%	Electrolytic — +5 V regulator output test point
C35	10 nF	25 V, 10%	Ceramic
C36	47 nF (Issue 2 only; not fitted on Issue 3)	25 V, 10%	Ceramic
C37, C38	33 pF	25 V, 10%	Ceramic
C39	10 nF	25 V, 10%	Ceramic
C40, C42	47 nF	25 V, 10%	Ceramic
C43	100 nF	25 V, 10%	Ceramic
C44, C45	100 µF	16 V, −10% +80%	Electrolytic — DC-DC converter area
C46	1 µF	50 V, −10% +80%	Electrolytic — service modification: fit a high-temperature type
C47	22 µF	10 V, −10% +80%	Electrolytic
C48	47 nF	25 V, 10%	Ceramic
C49	47 nF (Issue 2) / 47 nF + 560 pF (Issue 3)	25 V, 10%	Ceramic
C50	22 µF	10 V, −10% +80%	Electrolytic — +9 V regulator input test point
C52, C53	150 pF	25 V, 10%	Ceramic

Notes from the manual's modification history:

• If disc capacitors are used for C41 and C49 (47 nF) they must be handled per the manual's note — later production used a number of disc capacitors in place of the original axial types for the 47 nF and 100 nF values.
• C46 should be replaced by a high-temperature type — this is a specified service change, worth doing on any machine that still has the original.
• A 100 pF capacitor between RAS and ground and a 470 pF capacitor between IC2 pin 28 and ground appear as conditional modifications on some boards — only fitted where required.

Always verify against your own board's silkscreen: values were adjusted between issues, and the Spectrum+ can contain any of five board revisions.

Choosing replacements

• Use 105 °C aluminium electrolytics of equal capacitance and equal-or-higher voltage. The original 10 V and 16 V parts are comfortably replaced with 16 V or 25 V modern equivalents.
• Note the very wide original tolerances (−10% +80% on several parts) — modern ±20% capacitors are well within specification.
• Several originals are axial. Axial parts remain available; if fitting radial replacements, form and insulate the leads neatly so nothing shorts to adjacent tracks.
• The ceramics (47 nF, 100 nF, and the small pF values) are stable and are not normally replaced.

Replacement procedure

1. Unplug the power and open the case; disconnect the keyboard tails carefully.
2. Record the value, voltage and polarity of each electrolytic before removal.
3. Add fresh flux and solder to both joints and let it mix with the old solder.
4. Lift one lead at a time with the joint fully molten, then clear the hole with wick.
5. Fit the replacement the correct way round, solder and trim.
6. Inspect for bridges and splatter before reassembly.

Post-recap verification

1. Reconnect power and confirm the copyright screen appears.
2. Check the rails: +9 V ± 2.0 V at C50, +5 V ± 0.25 V at C34 with no discernible ripple, and −5 V / +12 V at IC6 pins 1 and 8.
3. Confirm the DC-DC converter coil is buzzing faintly.
4. Check the display is stable with no wavy lines.
5. Test sound, a tape load 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+
• Sinclair ZX Spectrum+ General Maintenance
• Sinclair ZX Spectrum+ Troubleshooting Guide
• Sinclair ZX Spectrum Capacitor Replacement Guide
• Sinclair ZX Spectrum +2 Capacitor Replacement Guide
• Capacitor Failure Symptoms