Editing Sinclair ZX Spectrum+ Capacitor Replacement Guide

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[[File:Sinclair ZX Spectrum 48K circuit diagram.png|thumb|420px|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.<ref name="sm48">''ZX Spectrum Service Manual'' (48K), Sinclair Research Ltd, Section 5 Parts Lists (capacitor table) and Section 4 (repair notes, supply test points, service modifications).</ref>

== ⚠️ 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.<ref name="sm48" />

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.<ref name="sm48" />

Pay particular attention to the area '''around the heatsink screws''', where hairline cracks in the board are a documented cause of intermittent faults.<ref name="sm48" />

== 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.<ref name="sm48" />

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.<ref name="sm48" />
* 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.'''<ref name="sm48" />

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''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:<ref name="sm48" />

* 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 ==

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

== Post-recap verification ==

# Reconnect power and confirm the copyright screen appears.
# 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.
# Confirm the DC-DC converter coil is buzzing faintly.
# Check the display is stable with no wavy lines.
# 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]]

== References ==

<references />

[[Category:Sinclair Computers]]
[[Category:Capacitor Replacement Guides]]