ZX Spectrum 16K/48K · Issue 2

Before you start

• The Spectrum 16K/48K uses an external 9 V DC power supply and makes the 5 V on the board itself, with the 7805 regulator ^[1]. 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: it has a transformer connected to the 230 V mains ^[1].
• Always work with the power supply unplugged from the mains and from the board. The converter on the board (TR4, TR5 and the coil) makes the +12 V and −5 V for the lower RAM; tired capacitors can make it fail and take the 4116s with it ^[6]. They are not easy to find.
• C46 has the wrong polarity on the silkscreen of this board ^[3][6]: fit the positive on the left, facing IC2 ^[4]. Before removing it, note which way round the old one was.
• Console5 gives 16 V and 25 V because it lists the replacement kit ^[4]; Sinclair gives 10 V for the 22 µF parts ^[1][2]. A higher voltage is fine, as long as the capacitor fits: SfE recommends 22 µF 25 V, 100 µF 25 V and 1 µF 63 V axials ^[6].
• Many Issue 2 boards have a 4.7 µF C74 (radial) soldered on top of other components, between the emitter of TR5 (the positive of C34) and the base of TR5, because Sinclair had it fitted to all of them ^[1][5]. It has no holes of its own, so it is not on the map. If you find it, replace it too, with 4.7 µF and at least 5 V ^[1][3].
• The capacitors near the heatsink run hotter: SfE recommends 105 °C parts for C27 and C47 ^[3][6]. Keep the iron at 300 °C at most, as the traces on these boards lift easily ^[6]. If you find broken traces or damaged chips, bring the board to the shop.