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ZX Spectrum 16K/48K · Issue 4B

Issue 4B has 12 through-hole axial electrolytics. Values and voltages from the parts list in Sinclair's supplement to the service manual [1], confirmed by the Spectrum for Everyone [2] and Console5 [3] lists. Together with the 4A, it was the first board to appear in many Spectrum+ machines [7]. We did not find a drawing of the 4B: the positions come from the neighbouring boards (3B and 6A, where these capacitors are in the same places [5][6]) and were checked against a photo of a 4B [4]. They are there to help you find your way.

12 capacitors

Issue 2Issue 3Issue 3BIssue 4AIssue 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 [8].
  • The 4B has the converter modification from the factory [1]: it has no C47 and it has C79 and C80, which earlier boards don't have [2][3]. A kit for the 3B or the 4A will not fit as it is.
  • On a Spectrum+ with this board, the reset button is wired to the legs of C27 [7]. When you replace it, solder the two wires back in the same places.
  • Console5 gives other voltages because it lists the replacement kit [3]; we follow Sinclair [1]. A higher voltage is fine, as long as the capacitor fits [2]. Keep the iron at 300 °C at most [8] 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][3]
C271 µF50 VAxial electrolytic[1][2][3]
C2822 µF10 VAxial electrolytic[1][2][3]
C3422 µF10 VAxial electrolytic[1][2][3]
C44100 µF16 VAxial electrolytic[1][2][3]
C45100 µF16 VAxial electrolytic[1][2][3]
C461 µF50 VAxial electrolytic[1][2][3]
C5022 µF10 VAxial electrolytic[1][2][3]
C6522 µF20 VAxial electrolytic[1][2][3]
C744.7 µF5 VAxial electrolytic[1][2][3]
C791 µF16 VAxial electrolytic[1][2][3]
C8022 µF25 VAxial electrolytic[1][2][3]

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.
1×1 µF16 VAxial electrolyticC79
2×1 µF50 VAxial electrolyticC27, C46
1×4.7 µF5 VAxial electrolyticC74
4×22 µF10 VAxial electrolyticC25, C28, C34, C50
1×22 µF20 VAxial electrolyticC65
1×22 µF25 VAxial electrolyticC80
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]ZX Spectrum: Capacitor Lists · Console5 Tech Wiki
  4. [4]Sinclair ZX Spectrum Issue 4B Motherboard (fotografia, domínio público) · Fernando Sáenz / AUIC, Wikimedia Commons
  5. [5]ZX Spectrum 48k Issue 6A board replica (KiCad, BOM interativo) · Paweł Mandes (GitHub), 2023
  6. [6]ZX Spectrum 48K Issue 3B, projeto KiCad sobre os Gerbers de PABB (CC0) · liveboxandy (GitHub), 2026
  7. [7]ZX Spectrum Models · Spectrum For Everyone
  8. [8]Recapping your Spectrum · Spectrum For Everyone