Sinclair ZX Spectrum+ Capacitor Replacement Guide

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

Capacitors on the Sinclair ZX Spectrum+. The Spectrum+ is, in Sinclair's own words, "basically the same as the 48k ZX Spectrum with a different keyboard and case, and a reset button" — but it is built on the later board issues, and those do not carry the same capacitor values as the rubber-key Issue 2 and Issue 3 boards.

An earlier version of this page reproduced Sinclair's section 8.5 table — the Issue 2 / Issue 3 list — and presented it as the Spectrum+ list. It is not. On the Spectrum+ boards C1–C8 are 22 nF rather than 47 nF, C49 is 560 pF rather than 47 nF, C63, C64, C77 and several others are not fitted at all on some issues, and C78 to C105 exist. The table below is Sinclair's own section 9.13, in full.

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, generated on board for the lower RAM. Board-level capacitor work here is low-voltage work.

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

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

Is it a recap candidate?

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

Capacitors do cause real symptoms here, and there is a neat diagnostic: if the screen shows wavy lines, press down on each electrolytic in turn. If the lines disappear while you press one, that is the capacitor.

Worthwhile targets:

• C50 — the regulator input and the service manual's +9 V test point
• C34 — the regulator output and the +5 V test point
• C44 and C45 — in the DC-DC converter area feeding the lower RAM
• C46 — Sinclair specifies a high-temperature type here as a service change
• Anything bulging, leaking, or that changes the symptom when pressed

Sinclair's capacitor list

Unless otherwise stated all capacitors are axial types. Read your board's issue number before using any column.

Sinclair's capacitor list, Service Manual section 9.13 — Spectrum+ board issues

Ref	Issue 4A	Issue 4B	Issue 5	Issue 6A	Rating / tolerance	Type	Note
C1–C8	22 nF	22 nF	22 nF	22 nF	25 V, 10%	Ceramic
C9–C24	Not used	Not used	Not used	Not used	—	—
C25	22 µF	22 µF	22 µF	22 µF	10 V, −10% +80%	Electrolytic
C26	22 nF	22 nF	22 nF	22 nF	25 V, 10%	Ceramic
C27	1 µF	1 µF	1 µF	1 µF	50 V, 10%	Electrolytic
C28	22 µF	22 µF	22 µF	22 µF	10 V, −10% +80%	Electrolytic
C29	47 nF	47 nF	44 nF	22 nF	25 V, 10%	Ceramic
C30	22 nF	22 nF	22 nF	22 nF	25 V, 10%	Ceramic	2
C31	100 nF	100 nF	100 nF	100 nF	25 V, 10%	Ceramic
C32	100 nF	100 nF	100 nF	100 nF	25 V, 10%	Ceramic	2
C33	22 nF	22 nF	22 nF	47 nF	25 V, 10%	Ceramic
C34	22 µF	22 µF	22 µF	22 µF	10 V, −10% +80%	Electrolytic
C35	10 nF	10 nF	10 nF	10 nF / 100 nF	25 V, 10%	Ceramic	2, 3
C36	Not used	Not used	Not used	Not used	—	—
C37, C38	33 pF	33 pF	33 pF	33 pF	25 V, 10%	Ceramic
C39	10 nF	10 nF	10 nF	10 nF	25 V, 10%	Ceramic
C40, C42	22 nF	22 nF	22 nF	22 nF	25 V, 10%	Ceramic
C43	100 nF	100 nF	100 nF	100 nF	25 V, 10%	Ceramic
C44, C45	100 µF	100 µF	Not used	100 µF	16 V, −10% +80%	Ceramic (as printed)
C46	1 µF	1 µF	1 µF	1 µF	50 V, −10% +80%	Electrolytic
C47	22 nF	22 nF	Not used	Not used	10 V, −10% +80%	Electrolytic
C48	22 nF	22 nF	22 nF	22 nF	25 V, 10%	Ceramic
C49	560 pF	560 pF	560 pF	560 pF	25 V, 10%	Ceramic
C50	22 µF	22 µF	22 µF	22 µF	10 V, −10% +80%	Electrolytic
C51	Not used	Not used	Not used	Not used	—	—
C52, C53	150 pF	150 pF	150 pF	150 pF	25 V, 10%	Ceramic	2
C54	Not used	Not used	Not used	Not used	—	—
C55–C60	22 nF	22 nF	22 nF	22 nF	25 V, 10%	Ceramic
C61	22 nF	Not used	22 nF	22 nF	25 V, 10%	Ceramic
C62	22 nF	22 nF	22 nF	22 nF	25 V, 10%	Ceramic
C63	47 pF	47 pF	Not used	Not used	25 V, 10%	Ceramic
C64	180 pF	180 pF	Not used	Not used	25 V, 10%	Ceramic
C65	22 µF	22 µF	22 µF	22 µF	20 V, −10% +80%	Electrolytic
C66	22 nF	22 nF	22 nF	22 nF	25 V, 10%	Ceramic
C67	100 pF	100 pF	100 pF	100 pF	25 V, 10%	Ceramic	2
C68–C71	100 nF	100 nF	100 nF	100 nF	25 V, 10%	Ceramic	2
C72, C73	16 pF	16 pF	16 pF	16 pF	25 V, 5%	Ceramic
C74	4.7 µF	4.7 µF	4.7 µF	4.7 µF	5 V minimum	Electrolytic
C75	100 nF	100 nF	100 nF	100 nF	25 V, 10%	Ceramic
C76	47 nF	47 nF	47 nF	22 nF	25 V, 10%	Ceramic	2
C77	100 nF	100 nF	Not used	Not used	25 V, 10%	Ceramic
C78	Not used	Not used	22 µF	Not used	25 V, 10%	Electrolytic
C79	Not used	1 µF	1 µF	1 µF	16 V, 10%	Electrolytic
C80	Not used	22 µF	Not used	22 µF	25 V, 10%	Electrolytic
C100	Not used	Not used	Not used	10 nF	25 V, 10%	Ceramic	4
C101	Not used	Not used	Not used	22 nF	25 V, 10%	Ceramic	4
C102, C103	Not used	Not used	Not used	Not used	—	—
C104	Not used	Not used	100 nF	100 nF	25 V, 10%	Ceramic
C105	Not used	Not used	180 pF	180 pF	25 V, 10%	Ceramic

The notes

Sinclair's note numbers in the last column, from section 9.12.1:

• 2 — on Issue 6 boards this part is not necessary with the SAGA version of IC1.
• 3 — on Issue 6 boards this part is not necessary with the FERRANTI version of IC1.
• 4 — on Issue 6 boards this is only required on VHF models.

C27 is an electrolytic

C27 is 1 µF, 50 V, electrolytic on every board issue Sinclair lists, in both section 8.5 and section 9.13. An earlier version of this page typed it as a ceramic. It matters: it is polarised, and on a Spectrum+ conversion the reset switch is connected across C27 on the top side of the board, so it is a part a rebuilder will be working near.

Two transistor traps

Not capacitors, but they sit in the same parts list and both will cost you a board:

• If TR4 is replaced with a KTC2236A-Y, the pin connections are different from every other replacement type — pin 1 is the emitter, pin 2 the collector and pin 3 the base, so the base and collector are reversed. TR4 drives the DC-DC converter that makes the −5 V and +12 V DRAM rails, and fitting it the usual way round will not end well.
• If TR3 is a KSC839, R24 should be 15 k.

Choosing replacements

• 105 °C aluminium electrolytics, equal capacitance, equal or higher voltage. The 10 V and 16 V originals are comfortably replaced with 16 V or 25 V modern parts.
• Note the very wide original tolerances — several parts are specified −10 % +80 %, so a modern ±20 % capacitor is well inside specification.
• Several originals are axial. Axial parts are still made; if you fit radial replacements, form and insulate the leads so nothing shorts to adjacent tracks.
• The ceramics are stable and are not a service item.

Replacement procedure

1. Unplug the power, open the case and disconnect the keyboard tails carefully — see Sinclair ZX Spectrum Keyboard Membrane Repair.
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 braid.
5. Fit the replacement the right way round, solder and trim.
6. Inspect for bridges and splatter before reassembly.

Post-recap checks

1. Confirm the copyright screen appears.
2. +9 V ± 2.0 V at C50 and +5 V at C34, with no discernible ripple.
3. −5 V at IC6 pin 1 and +12 V at IC6 pin 8. The −5 V test point is IC6 pin 1, not the collector of TR4.
4. The DC-DC converter coil should buzz faintly.
5. Stable display, no wavy lines.
6. Sound, a tape load, and every key.

If something that worked before the recap has stopped, 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
• Sinclair ZX Spectrum Capacitor Replacement Guide
• Sinclair ZX Spectrum Keyboard Membrane Repair
• Sinclair ZX Spectrum Service Manual
• Capacitor Failure Symptoms