Editing Sinclair ZX Spectrum Capacitor Replacement Guide

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[[File:Sinclair ZX Spectrum Issue 3 circuit diagram.png|thumb|420px|Sinclair's Issue 3 circuit diagram. The regulator, the TR4/TR5 inverter and the capacitors around them are at the bottom left.]]

This guide covers the capacitors on the original rubber-key '''[[Sinclair ZX Spectrum]]''' (16K and 48K), board Issues 1 to 6A. Every designator, value, voltage rating and tolerance below is taken from the parts lists in Sinclair's own ''ZX Spectrum Service Manual'', which is [[Sinclair ZX Spectrum Service Manual|hosted on this wiki]].<ref name="sm85">''ZX Spectrum Service Manual'', Sinclair Research Ltd, section 8.5, "Capacitors - all axial types unless otherwise stated" (parts list for the Issue 2 and Issue 3 boards, including the Issue 2 modification column). Hosted on this wiki as [[:File:Sinclair ZX Spectrum Service Manual.pdf]].</ref><ref name="sm913">''ZX Spectrum Service Manual'', Sinclair Research Ltd, Supplement No. 1, section 9.13, "Capacitors - unless otherwise stated all are axial types" (parts list for the Issue 4A, 4B, 5 and 6A boards). Hosted on this wiki as [[:File:Sinclair ZX Spectrum Service Manual.pdf]].</ref>

For the later machines, which use different boards, see the [[Sinclair ZX Spectrum+ Capacitor Replacement Guide|Spectrum+]], [[Sinclair ZX Spectrum 128 Capacitor Replacement Guide|Spectrum 128]] and [[Sinclair ZX Spectrum +2 Capacitor Replacement Guide|Spectrum +2]] guides.

== Is the Spectrum a recap candidate? ==

'''No — not as a matter of course.''' The Spectrum uses ordinary leaded electrolytics and has no systematic capacitor-failure problem. There is no reason to shotgun every capacitor on a board that works.

Capacitors do nevertheless cause real, documented faults here, and Sinclair published a neat test for it: if the picture shows '''wavy lines''', press down on each electrolytic in turn with the machine running. If the lines disappear while you are pressing one, that is the faulty capacitor.<ref name="sm6">''ZX Spectrum Service Manual'', Sinclair Research Ltd, section 6 (fault diagnosis and repair - input/output), covering 6.1 TR4 faults, 6.2 no video, 6.3 corrupt paper, 6.4 video incorrect, 6.7 keyboard, 6.8 regulator coil and 6.9 speaker.</ref>

Worth attention on any board:

* '''C50''' and '''C34''' — the regulator input and output. These are Sinclair's own supply test points, so a rail that is out of tolerance or visibly rippling points straight at them.<ref name="sm5">''ZX Spectrum Service Manual'', Sinclair Research Ltd, section 5 (fault diagnosis and repair - PSU and memory): 5.2 power supply unit, 5.3.1 basic checks table, 5.4 memory check and the RAM bit-to-IC table, 5.5 keyboard structure.</ref>
* '''C44''' and '''C45''' — the rectifier smoothing for the +12 V and +12 VA rails produced by the TR4/TR5 inverter. C44 is one of the parts to check when the inverter has failed short.<ref name="sm6" /><ref name="iss3cd">''ZX Spectrum - Issue 3'' circuit diagram, Sinclair Research Ltd. Hosted on this wiki as [[:File:Sinclair ZX Spectrum Issue 3 circuit diagram.png]]. Source for circuit positions, rail derivation and the edge-connector pinout quoted on this page.</ref>
* '''C46''' — Sinclair specified this be replaced with a '''high-temperature''' component as a service modification, on all units.<ref name="sm4">''ZX Spectrum Service Manual'', Sinclair Research Ltd, section 4 (fault diagnosis and repair - getting started): 4.1.2 modification history, 4.2 modifications to the Issue 1 board, 4.3 modifications to the Issue 2 board, 4.4 modifications to the Issue 3B board, 4.5 the 32K extension memory, 4.6 Hitachi vs NEC ROM links; and section 8.2, notes to the parts list.</ref>
* '''C65''' — implicated by Sinclair in a dim picture, where it has gone high-impedance.<ref name="sm6" />
* Anything bulging, leaking, or that changes the symptom when you press it.

== Which board have you got? ==

This matters more on the Spectrum than on most machines: '''the capacitor complement genuinely differs between board issues.''' C1–C8 are 47 nF on Issue 2 and Issue 3 but 22 nF from Issue 4A onwards; C44 and C45 are not fitted at all on Issue 5; C47 disappears after Issue 4B; C78, C79 and C80 exist only on the later boards. A capacitor list that does not say which issue it applies to is wrong even where the numbers happen to be right for one of them.

Sinclair shipped Issue 1, 2, 3, 3B, 4A, 4B, 5 and 6A boards. '''There was no Issue 4 and no Issue 6''' — neither was ever issued.<ref name="sm9">''ZX Spectrum Service Manual'', Sinclair Research Ltd, Supplement No. 1, sections 9.1 to 9.11: introduction, DC-DC converter modification, and the descriptions of the Issue 3B, 4A, 4B, 5 and 6A boards, the servicing addenda and the warranty seal.</ref>

The issue number is printed on the board. Work from it.

{| class="wikitable styled-table" style="width:95%; text-align:left;"
|+'''Board issues and what changed'''
! Issue !! Notes
|-
| 1 || The 16K RAM is on the main board; the 32K extension is a subsidiary board on special DIL connectors. Approximately 26,000 units were made. '''Sinclair published no separate Issue 1 capacitor parts list''', and none is reconstructed here<ref name="sm4" />
|-
| 2 || All 48K of RAM can be fitted directly to the board. Has the colour presets VR1/VR2 and trimmers TC1/TC2. Some early units used disc capacitors where axials were later fitted<ref name="sm4" />
|-
| 3 || Colour tuning made automatic, so the presets and trimmers are gone; allows OKI parts in the extension memory; the heatsink is redesigned and moved to the back of the case<ref name="sm4" />
|-
| 3B || Functionally like Issue 3 but a different layout, with an improved DC converter: C77 (100 nF) added, C49 changed from 47 nF to 560 pF, R60 from 270 R to 68 R<ref name="sm4" />
|-
| 4A || R32 deleted; two spare gates of IC24 used to improve ULA timing, which requires ULA 6C001-7 or later<ref name="sm9" />
|-
| 4B || Issue 4A plus the DC-DC converter modification. C61 was omitted for want of board space and reinstated on later issues<ref name="sm9" />
|-
| 5 || Only 1,000 boards were supplied, UK market only. A single ULA (IC27, Mullard ZX 84/01) replaces six 74LS packages, and IC28 is added<ref name="sm9" />
|-
| 6A || Like Issue 5, but IC1 may be a Ferranti or a SAGA part<ref name="sm9" />
|}

== Capacitors, by board issue ==

Sinclair's two parts lists, combined. '''Unless otherwise stated all are axial types.'''<ref name="sm85" /><ref name="sm913" />

{| class="wikitable styled-table" style="width:100%; text-align:left; font-size:95%;"
|+'''ZX Spectrum 16K/48K main board capacitors'''
! Ref !! Issue 2 !! Issue 3 !! Issue 4A !! Issue 4B !! Issue 5 !! Issue 6A !! Rating / tol. !! Type
|-
| C1–C8 || 47 nF || 47 nF || 22 nF || 22 nF || 22 nF || 22 nF || 25 V, 10% || Ceramic
|-
| C9–C24 || colspan="6" style="text-align:center;" | Not used || ||
|-
| C25 || 22 µF || 22 µF || 22 µF || 22 µF || 22 µF || 22 µF || 10 V, −10% +80% || '''Electrolytic'''
|-
| C26 || 47 nF || 47 nF || 22 nF || 22 nF || 22 nF || 22 nF || 25 V, 10% || Ceramic
|-
| C27 || 1 µF || 1 µF || 1 µF || 1 µF || 1 µF || 1 µF || 50 V || '''Electrolytic'''
|-
| C28 || 22 µF || 22 µF || 22 µF || 22 µF || 22 µF || 22 µF || 10 V, −10% +80% || '''Electrolytic'''
|-
| C29 || 47 nF || 47 nF || 47 nF || 47 nF || 47 nF (printed "44nf" — see below) || 22 nF || 25 V, 10% || Ceramic
|-
| C30 || 47 nF || 47 nF || 22 nF || 22 nF || 22 nF || 22 nF || 25 V, 10% || Ceramic
|-
| C31 || 100 nF || 100 nF || 100 nF || 100 nF || 100 nF || 100 nF || 25 V, 10% || Ceramic
|-
| C32 || 100 nF || 100 nF || 100 nF || 100 nF || 100 nF || 100 nF || 25 V, 10% || Ceramic
|-
| C33 || 47 nF || 47 nF || 22 nF || 22 nF || 22 nF || 47 nF || 25 V, 10% || Ceramic
|-
| C34 || 22 µF || 22 µF || 22 µF || 22 µF || 22 µF || 22 µF || 10 V, −10% +80% || '''Electrolytic'''
|-
| C35 || 10 nF || 10 nF || 10 nF || 10 nF || 10 nF || 10 nF (100 nF with the Ferranti ULA) || 25 V, 10% || Ceramic
|-
| C36 || 47 nF || Not fitted || Not used || Not used || Not used || Not used || 25 V, 10% || Ceramic
|-
| C37, C38 || 33 pF || 33 pF || 33 pF || 33 pF || 33 pF || 33 pF || 25 V, 10% || Ceramic
|-
| C39 || 10 nF || 10 nF || 10 nF || 10 nF || 10 nF || 10 nF || 25 V, 10% || Ceramic
|-
| C40, C42 || 47 nF || 47 nF || 22 nF || 22 nF || 22 nF || 22 nF || 25 V, 10% || Ceramic
|-
| C43 || 100 nF || 100 nF || 100 nF || 100 nF || 100 nF || 100 nF || 25 V, 10% || Ceramic
|-
| C44, C45 || 100 µF || 100 µF || 100 µF || 100 µF || '''Not used''' || 100 µF || 16 V, −10% +80% || '''Electrolytic'''
|-
| C46 || 1 µF || 1 µF || 1 µF || 1 µF || 1 µF || 1 µF || 50 V, −10% +80% || '''Electrolytic'''
|-
| C47 || 22 µF || 22 µF || 22 µF || 22 µF || '''Not used''' || '''Not used''' || 10 V, −10% +80% || '''Electrolytic'''
|-
| C48 || 47 nF || 47 nF || 22 nF || 22 nF || 22 nF || 22 nF || 25 V, 10% || Ceramic
|-
| C49 || 47 nF || 47 nF (560 pF from Issue 3B) || 560 pF || 560 pF || 560 pF || 560 pF || 25 V, 10% || Ceramic
|-
| C50 || 22 µF || 22 µF || 22 µF || 22 µF || 22 µF || 22 µF || 10 V, −10% +80% || '''Electrolytic'''
|-
| C51 || colspan="6" style="text-align:center;" | Not used || ||
|-
| C52, C53 || 150 pF || 150 pF || 150 pF || 150 pF || 150 pF || 150 pF || 25 V, 10% || Ceramic
|-
| C54 || 470 pF || Not fitted || Not used || Not used || Not used || Not used || 25 V, 10% || Ceramic
|-
| C55–C60 || 47 nF || 47 nF || 22 nF || 22 nF || 22 nF || 22 nF || 25 V, 10% || Ceramic
|-
| C61 || 47 nF || 47 nF || 22 nF || '''Not used''' || 22 nF || 22 nF || 25 V, 10% || Ceramic
|-
| C62 || 47 nF || 47 nF || 22 nF || 22 nF || 22 nF || 22 nF || 25 V, 10% || Ceramic
|-
| C63 || 47 pF || 47 pF || 47 pF || 47 pF || Not used || Not used || 25 V, 10% || Ceramic
|-
| C64 || 100 pF || 100 pF || 180 pF || 180 pF || Not used || Not used || 25 V, 10% || Ceramic
|-
| C65 || 100 µF (22 µF after the colour modification) || 22 µF || 22 µF || 22 µF || 22 µF || 22 µF || 20 V, −10% +80% || '''Electrolytic'''
|-
| C66 || 47 nF || 47 nF || 22 nF || 22 nF || 22 nF || 22 nF || 25 V, 10% || Ceramic
|-
| C67 || Not fitted (100 pF once modified) || 100 pF || 100 pF || 100 pF || 100 pF || 100 pF || 25 V, 10% || Ceramic
|-
| C68–C71 || Not fitted || 100 nF || 100 nF || 100 nF || 100 nF || 100 nF || 25 V, 10% || Ceramic
|-
| C72, C73 || Not fitted || 16 pF || 16 pF || 16 pF || 16 pF || 16 pF || 25 V, 5% || Ceramic
|-
| C74 || Not fitted (47 µF once modified) || 4.7 µF || 4.7 µF || 4.7 µF || 4.7 µF || 4.7 µF || 5 V minimum || '''Electrolytic'''
|-
| C75 || Not fitted || 100 nF || 100 nF || 100 nF || 100 nF || 100 nF || 25 V, 10% || Ceramic
|-
| C76 || Not fitted || 47 nF || 47 nF || 47 nF || 47 nF || 22 nF || 25 V, 10% || Ceramic
|-
| C77 || Not fitted || Added on Issue 3B (100 nF) || 100 nF || 100 nF || Not used || Not used || 25 V, 10% || Ceramic
|-
| C78 || Not fitted || Not fitted || Not used || Not used || 22 µF || Not used || 25 V || '''Electrolytic'''
|-
| C79 || Not fitted || Not fitted || Not used || 1 µF || 1 µF || 1 µF || 16 V, 10% || '''Electrolytic'''
|-
| C80 || Not fitted || Not fitted || Not used || 22 µF || Not used || 22 µF || 25 V || '''Electrolytic'''
|-
| C100 || Not fitted || Not fitted || Not used || Not used || Not used || 10 nF (VHF models only) || 25 V, 10% || Ceramic
|-
| C101 || Not fitted || Not fitted || Not used || Not used || Not used || 22 nF (VHF models only) || 25 V, 10% || Ceramic
|-
| C104 || Not fitted || Not fitted || Not used || Not used || 100 nF || 100 nF || 25 V, 10% || Ceramic
|-
| C105 || Not fitted || Not fitted || Not used || Not used || 180 pF || 180 pF || 25 V, 10% || Ceramic
|}

'''C41''' appears in Sinclair's modification notes as a 47 nF part that should be an axial rather than a disc type, but it is not listed in either parts-list table; neither is a value for it given anywhere else in the manual. It is therefore not tabulated above.<ref name="sm4" />

=== Where the two parts lists disagree with themselves ===

Sinclair's tables contain several obvious misprints. They are recorded here so that you can check this page against the manual and see why it differs:<ref name="sm85" /><ref name="sm913" />

* '''C44/C45''' are given as type "Ceramic" in section 9.13 but "Electrolytic" in section 8.5. A 100 µF part with a −10% +80% tolerance is an electrolytic; the 9.13 type cell is wrong.
* '''C47''' is given as "22nf" in section 9.13, with an electrolytic type and a 10 V, −10% +80% rating. Section 8.5 and the DC-DC converter modification in section 9.2 both call it a 22 µF electrolytic. It is 22 µF.
* '''C29''' on Issue 5 is printed as "44nf", which is not a preferred value. The table above shows 47 nF, matching every other issue except 6A, but that is an inference and not what the manual prints — check your own board.
* '''C78''' is 1 µF 25 V in section 9.2 but 22 µF 25 V in the section 9.13 parts list. Section 9.2 carries the editor's warning that its instructions are incorrect, so the parts list is the better record.

Every one of these is flagged rather than quietly corrected, so that this page can be checked line by line against the manual.

== The electrolytics — the actual shopping list ==

These are the service items. Everything else on the board is ceramic and is not normally replaced.<ref name="sm85" /><ref name="sm913" />

{| class="wikitable styled-table" style="width:90%; text-align:left;"
|+'''Electrolytics by board issue'''
! Board !! Electrolytics fitted
|-
| Issue 2 / Issue 3 || C25, C27, C28, C34, C44, C45, C46, C47, C50, C65, and C74 on Issue 3 (or on an Issue 2 board that has had the modification)
|-
| Issue 4A || C25, C27, C28, C34, C44, C45, C46, C47, C50, C65, C74
|-
| Issue 4B || As Issue 4A, plus C79 and C80
|-
| Issue 5 || C25, C27, C28, C34, C46, C50, C65, C74, C78, C79 — '''no C44, C45 or C47'''
|-
| Issue 6A || C25, C27, C28, C34, C44, C45, C46, C50, C65, C74, C79, C80 — '''no C47'''
|}

=== Choosing replacements ===

* Use '''105 °C''' aluminium electrolytics, equal capacitance, equal or higher voltage. The original 10 V, 16 V and 20 V parts are comfortably replaced by 16 V, 25 V or 35 V modern equivalents.
* Note how wide the original tolerances are — several parts are specified −10% +80%. A modern ±20% capacitor is well inside Sinclair's specification.
* '''C46 should be a high-temperature type.''' Sinclair made this a service change to be applied to all units, so it is worth doing on any board still carrying the original.<ref name="sm4" />
* '''C74 is essential on Issue 2 boards and should be fitted retrospectively if missing''', and R60 must be changed to the larger value at the same time.<ref name="sm4" />
* Sinclair's originals are '''axial''' unless the parts list says otherwise. Axials are still made; if you fit radial parts instead, form and sleeve the leads so nothing can touch an adjacent track.
* '''No lead-pitch or body-height figures are given here.''' Sinclair published none, and the case clearance depends on which board issue and which heatsink you have. Measure your own board.

== Replacement procedure ==

# '''Unplug the supply.''' There are no mains voltages inside the computer: it runs from an external 9 V pack and the highest rail on the board is +12 V.<ref name="sm1">''ZX Spectrum Service Manual'', Sinclair Research Ltd, section 1.11, "Power Supplies" - the external 9 V requirement and the derivation of the internal +5 V, −5 V, +12 V and +12 VA rails.</ref>
# '''Open the case.''' Five self-tapping screws in the base, and one more holding the board.<ref name="sm7">''ZX Spectrum Service Manual'', Sinclair Research Ltd, section 2.1 (disassembly), section 7.2 (repair) and section 8.4 (case assembly parts list).</ref>
# '''Withdraw the keyboard tails''' from KB1 (5-way) and KB2 (8-way). Pull them straight. Sinclair's own instruction is that the ribbon connectors must be fully inserted and not kinked during insertion; they crack where they bend.<ref name="sm7" />
# '''Record value, voltage and polarity''' of every electrolytic before you remove it.
# '''Add fresh flux and solder''' to the old joints and let it mix before wicking. Use an earthed, low-power iron and recognised desoldering technique — Sinclair's own instruction, aimed at not lifting pads.<ref name="sm7" />
# '''Fit the replacements the right way round''', solder and trim.
# '''Inspect for solder splatter''' under magnification before reassembly. The manual is explicit that hairline splatter can measure several ohms and produce very misleading fault symptoms.<ref name="sm5" />
# '''Check the heatsink.''' If you disturbed the regulator, make sure it makes good contact with its heatsink, apply thermal grease to the back of its body, and on an Issue 3 board make sure the heatsink is positioned away from the edge connector — the fixing hole allows enough play to foul it.<ref name="sm7" />

== Checks after the work ==

Sinclair's own setting-up voltage check, with the machine out of the case.<ref name="sm3">''ZX Spectrum Service Manual'', Sinclair Research Ltd, section 3.1.2, "Voltage Check" - the internally generated supply voltages and their tolerances.</ref> IC6 is one of the lower-RAM 4116 devices, which is where all three rails meet.

{| class="wikitable styled-table" style="width:90%; text-align:left;"
|+'''Internal supply voltages'''
! Test point !! Nominal !! Tolerance !! Source
|-
| IC6 pin 9 || +5 V || ±0.25 V || <ref name="sm3" />
|-
| IC6 pin 1 || −5 V || −5.5 V to −4 V || <ref name="sm3" />
|-
| IC6 pin 8 || +12 V || ±1.2 V || <ref name="sm3" />
|-
| LT side of C52 || +12 VA || ±1.2 V || <ref name="sm3" />
|-
| Positive side of C50 (regulator input) || +9 V || ±2.0 V; below +7 V the regulator will not function correctly || <ref name="sm5" />
|-
| Positive side of C34 (regulator output) || +5 V || ±0.25 V, with no discernible ripple || <ref name="sm5" />
|}

'''Sinclair published no ripple figure in millivolts''', for any rail. The manual's criterion is "no discernible ripple" at the regulator output, and none is invented here.<ref name="sm5" />

Then confirm the machine initialises to a clear screen with the copyright message in the lower left, that the picture is stable with no wavy lines, and that sound, tape and the whole keyboard work.<ref name="sm5" />

== The rails, and why the Spectrum has three ==

Unlike the [[Sinclair ZX81|ZX81]] and [[Sinclair ZX80|ZX80]], which have a single +5 V rail, the Spectrum generates three supplies on board from the single external 9 V input:<ref name="sm1" /><ref name="iss3cd" />

* '''+5 V''' from a 7805 regulator, for the logic, the ULA and the modulator.
* '''−5 V and +12 V''' for the 4116 lower RAM, produced by the TR4/TR5 inverter, which raises the 9 V input above 12 V. The square wave at the junction of the TR4 collector and the inverter coil is rectified and smoothed by D15/C44.
* '''+12 VA''' for the colour circuits, taken from the same rectifier through R62/C45 so that it is free of the switching noise the RAM generates. It is also available on the expansion port.

This is the reason the +12 V and −5 V rails matter on a 16K/48K Spectrum and not on a 128 — the 4116 DRAM needs all three supplies, and the later machines' RAM does not.

'''Failure of TR4 is a significant cause of problems''' in Sinclair's own words, and the recommended DC-DC converter modification is specifically aimed at units in which either TR4 or the 16K DRAM has blown.<ref name="sm4" /><ref name="sm9" /> If a recap has not cured a rail fault, that circuit is where to look next; the symptom-by-symptom treatment is in the [[Sinclair ZX Spectrum Troubleshooting Guide]].

== Tools and materials ==

See [[Recommended Tools]]. For this job specifically:

* Earthed, temperature-controlled iron with a fine tip, and normal anti-static precautions<ref name="sm7" />
* Desoldering braid and/or a pump
* 63/37 leaded solder and fresh flux
* 105 °C aluminium electrolytics to the list above for '''your''' board issue
* Thermal grease, if the regulator comes off
* Isopropyl alcohol, a soft antistatic brush and magnification

== Notes ==

* '''Check the power supply before you fit new capacitors.''' A supply that is out of specification will simply damage the new ones. The external pack is unregulated and the polarity is unusual — see [[Sinclair ZX Spectrum General Maintenance]].
* If a previously working function fails after a recap, check the polarity of every capacitor you replaced before looking anywhere else.
* See [[Capacitor Failure Symptoms]] for general failure modes, and [[Battery Explosion, Capacitor or Corrosion Damage]] if there is corrosion to clean up.

== Related pages ==

* [[Sinclair ZX Spectrum]]
* [[Sinclair ZX Spectrum General Maintenance]]
* [[Sinclair ZX Spectrum Troubleshooting Guide]]
* [[Sinclair ZX Spectrum Service Manual]]
* [[Sinclair ZX Spectrum+ Capacitor Replacement Guide]]
* [[Sinclair ZX Spectrum 128 Capacitor Replacement Guide]]
* [[Capacitor Failure Symptoms]]

== References ==

<references />

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