Sinclair ZX Spectrum Capacitor Replacement Guide: Difference between revisions
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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). | * '''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. | * '''Leaking electrolyte''' – brown or green crust at the base of a capacitor. | ||
| Line 14: | Line 12: | ||
If '''any''' capacitor shows signs of failure, it is strongly recommended to replace '''all''' electrolytics on the board. | 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. | 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;" | {| class="wikitable styled-table" style="width:100%; text-align:center;" | ||
|+'''ZX Spectrum Mainboard Electrolytic Capacitors''' | |+'''ZX Spectrum Mainboard Electrolytic Capacitors''' | ||
| Line 49: | Line 47: | ||
''Some early Issue 1 boards have minor differences; always check your board.'' | ''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. | 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. | ||
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''The +2A/+3 models use a different PCB and power supply; consult their specific service manuals for capacitor lists.'' | ''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. | # '''Disassemble''' – Remove case screws, carefully separate keyboard membrane from mainboard. | ||
# '''Label keyboard and speaker leads.''' | # '''Label keyboard and speaker leads.''' | ||
| Line 82: | Line 80: | ||
# '''Reassemble and test''' – Power up with a known-good supply. | # '''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;" | {| class="wikitable styled-table" style="width:80%; text-align:center;" | ||
|+'''Expected Rails – BASIC prompt, no peripherals''' | |+'''Expected Rails – BASIC prompt, no peripherals''' | ||
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''Excessive ripple can cause video instability or RAM errors.'' | ''Excessive ripple can cause video instability or RAM errors.'' | ||
== | == Recommended Tools & Parts == | ||
* 40–60 W temperature-controlled soldering iron (fine tip) | * 40–60 W temperature-controlled soldering iron (fine tip) | ||
* Solder wick and/or desoldering pump | * Solder wick and/or desoldering pump | ||
| Line 104: | Line 102: | ||
* Kapton tape (to insulate capacitors near the modulator or case) | * 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. | * '''Check your power supply first!''' A faulty PSU can damage new capacitors and ICs. | ||
* '''Replace all electrolytics at once''' – partial recaps are not recommended. | * '''Replace all electrolytics at once''' – partial recaps are not recommended. | ||
| Line 112: | Line 110: | ||
* If you have video mods (composite, S-Video), ensure you use quality capacitors in the video path (C1, C3, C6, C27). | * 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 Troubleshooting Guide]] | ||
* [[Sinclair ZX Spectrum Power Supply Repair]] | * [[Sinclair ZX Spectrum Power Supply Repair]] | ||
* [[Sinclair ZX Spectrum Composite Video Mod]] | * [[Sinclair ZX Spectrum Composite Video Mod]] | ||
[[Category:Sinclair Computers]] | |||
[[Category:Sinclair | |||
[[Category:Capacitor Replacement Guides]] | [[Category:Capacitor Replacement Guides]] | ||
Latest revision as of 10:43, 12 May 2025
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
[edit | edit source]- 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
[edit | edit source]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)
[edit | edit source]| 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
[edit | edit source]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
[edit | edit source]- 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
[edit | edit source]| 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
[edit | edit source]- 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
[edit | edit source]- 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).