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ZX Spectrum 16K/48K · Issue 4A

Issue 4A has 11 through-hole axial electrolytics, the same as the 3B. Values and voltages from the parts list in Sinclair's supplement to the service manual [1], confirmed by the Spectrum for Everyone list [2]. We did not find an exact drawing of this board: the positions were measured on Sinclair's component drawing [3] and are there to help you find your way. It was the first board to appear in many Spectrum+ machines [5].

11 capacitors

Issue 2Issue 3Issue 3BIssue 4BIssue 6A

Before you start

  • The Spectrum 16K/48K and the Spectrum+ use an external 9 V DC power supply and make the 5 V on the board itself, with the 7805 regulator. Before you power it up, check that the supply is the right one and that the voltage and plug polarity match the label on the original supply: a supply with the wrong polarity can damage the computer. Don't open the power supply: the 230 V side is dangerous.
  • Always work with the power supply unplugged from the mains and from the board. The converter on the board makes the +12 V and −5 V for the lower RAM; tired capacitors can make it fail and take the 4116s with it [6].
  • Some 4A boards left the factory with the converter modification already done [1], which removes C47 and adds other components. If C47 is not there, it is not a fault. On the 4B this modification became part of the board layout [1].
  • On a Spectrum+ with this board, the reset button is wired to the legs of C27 [5]. When you replace it, solder the two wires back in the same places.
  • A higher voltage is fine, as long as the capacitor fits [2]: SfE recommends 22 µF 25 V, 100 µF 25 V, 1 µF 63 V and 4.7 µF 63 V axials [6]. Keep the iron at 300 °C at most [6] and check each reference and the polarity mark on the silkscreen before desoldering. If you find broken traces or damaged chips, bring the board to the shop.
RF modulatorEARMICExpansion portPower 9 VRegulator 7805ULA Ferranti (IC1)CPU Z80A (IC2)ROM (IC5)LM1889 (IC14)Lower RAM 4116 (IC6-IC13)Upper RAM (IC15-IC18)Upper RAM (IC19-IC22)Keyboard (KB1)Keyboard (KB2)
Axial electrolyticBoard seen from above, rear connectors at the top.Approximate positions: always check the reference printed on the board.

All capacitors

Ref.ValueVoltageTypeDiameter[n]
C2522 µF10 VAxial electrolytic[1][2]
C271 µF50 VAxial electrolytic[1][2]
C2822 µF10 VAxial electrolytic[1][2]
C3422 µF10 VAxial electrolytic[1][2]
C44100 µF16 VAxial electrolytic[1][2]
C45100 µF16 VAxial electrolytic[1][2]
C461 µF50 VAxial electrolytic[1][2]
C4722 µF10 VAxial electrolytic[1][2]
C5022 µF10 VAxial electrolytic[1][2]
C6522 µF20 VAxial electrolytic[1][2]
C744.7 µF5 VAxial electrolytic[1][2]

Shopping list

Quantities by value and voltage. Use new capacitors with the same capacitance and the same voltage or higher, that fit in the same space.

QtyValueVoltageTypeRef.
2×1 µF50 VAxial electrolyticC27, C46
1×4.7 µF5 VAxial electrolyticC74
5×22 µF10 VAxial electrolyticC25, C28, C34, C47, C50
1×22 µF20 VAxial electrolyticC65
2×100 µF16 VAxial electrolyticC44, C45

Sources

  1. [1]Sinclair ZX Spectrum / ZX Spectrum+ Service Manual, rev. 1.3, Suplemento n.º 1 (Issues 4A, 4B, 5 e 6A): lista de peças · Sinclair Research; transcrição de Brendan Alford, Spectrum For Everyone
  2. [2]Capacitor Lists (48K Range) · Spectrum For Everyone
  3. [3]Issue 4A Layout, do Suplemento n.º 1 do manual de serviço · Sinclair Research, via Spectrum For Everyone
  4. [4]ZX Spectrum 48K Issue 3B, projeto KiCad sobre os Gerbers de PABB (CC0) · liveboxandy (GitHub), 2026
  5. [5]ZX Spectrum Models · Spectrum For Everyone
  6. [6]Recapping your Spectrum · Spectrum For Everyone