ZX Spectrum 16K/48K · Issue 3B

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 makes the +12 V and −5 V for the lower RAM; tired capacitors can make it fail and take the 4116s with it ^[9]. The 3B already has an improved converter compared with Issue 3 ^[1][2], but the electrolytics are the same.
• On some boards C47 was removed by a service modification, and you may find two extra capacitors soldered by hand: a 22 µF C78 under the right-hand keyboard connector and a 1 µF C79 in place of diode D16 ^[3]. They are not on the map because they are not on every board. If you have them, replace them with the same value and note the orientation before removing them.
• 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 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, 1 µF 63 V and 4.7 µF 63 V axials ^[9].
• Keep the iron at 300 °C at most, as the traces on these boards lift easily ^[9]. Check each reference on the silkscreen and the polarity mark before desoldering. If you find broken traces or damaged chips, bring the board to the shop.