Sinclair ZX Spectrum +3 Capacitor Replacement Guide
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The Sinclair ZX Spectrum +3 has few electrolytic capacitors. Amstrad's electrical parts list for the Z70830 main board names seven, and the circuit diagram of the FD-1 EME-156 disk drive in the same manual shows seven more on the drive's controller board.[1] Amstrad removed the earlier Spectrums' DC-DC converter from this board, and the rails come straight from the external supply.[2]
Main board (Z70830)
[edit | edit source]| Ref | Value | Amstrad part | Where it sits |
|---|---|---|---|
| C8 | 100 µF 16 V | 20028 | Across the DC power input |
| C29 | 100 µF 16 V | 20028 | Supply to the UHF modulator stage (with C28) |
| C30 | 100 µF 16 V | 20028 | Supply to the UHF modulator stage (with C31) |
| C13 | 1 µF 50 V | 20062 | Beside the reset circuit (R3) |
| C27 | 1 µF 50 V | 20062 | See note below |
| C38 | 1 µF 50 V | 20062 | Sound circuit |
| C41 | 1 µF 50 V | 20062 | Sound output (fitted only on the +3) |
Values and part numbers: Amstrad's parts list.[1] Positions: Amstrad's circuit diagram and the redrawn schematic at zxnet.co.uk.[1][3]
Notes on the list:
- Amstrad's circuit diagram marks C27 as "10uf", while its parts list and the redrawn schematic both give 1 µF. Read the part on your own board before ordering.[1][3]
- C48, a 1 µF capacitor in the cassette circuit, is fitted only to the +2A built on this board, and the cassette deck's own capacitors (C100 onwards) belong to the +2A as well.[1][3]
- The diagram labels C51 "22uf", but the factory modification on issue 1 boards, where C51 is soldered on the copper side, uses a 22 nF part.[4] It is not an electrolytic.
- A Peritel-only version without the RF output omits C29 along with the modulator parts.[1]
Disk drive (FD-1 EME-156)
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| Ref | Value | Where it sits |
|---|---|---|
| C21 | 47 µF 16 V | +12 V input at J2 |
| C22 | 100 µF 6.3 V | +5 V input at J2 |
| C23 | 0.47 µF 50 V | Step delay timing of IC1 (M51017AP, pin 31) |
| C24 | 3.3 µF 50 V | Stepper power-down timing of IC1 (pin 34) |
| C25 | 22 µF 50 V | Circuit around Q5 to Q7 |
| C26 | 1 µF 50 V | Circuit around Q5 to Q7 |
| C27 | 10 µF 16 V | Circuit around Q5 to Q7 |
Source: Amstrad's drive circuit diagram.[1] The drive's designators are separate from the main board's, so drive C27 is not main-board C27. DataServe Retro reports that several types of 3-inch drive were fitted to the +3, of which the EME-156 is the most common; check which drive you have before using this list.[5] The spindle motor carries its own speed control (VR201 in Amstrad's flow chart), and the manual gives no values for its board.[1]
Power supply
[edit | edit source]The external supply appears in Amstrad's parts list only as part 173034, with no circuit or parts list. Read the values off the parts in your own supply. Warning: the supply's primary side works at mains voltage and its reservoir capacitor stays charged after unplugging; discharge and measure it before touching the primary side. After any repair, Amstrad's manual requires a 4 kV flash test and a 400 V DC insulation test reading at least 2 MΩ.[1]
Procedure
[edit | edit source]- Unplug the supply. Open the case and remove the drive as on Sinclair ZX Spectrum +3 General Maintenance.[5]
- Photograph the board and note the value, voltage and polarity of each electrolytic before removing it.
- Remove each part with a desoldering tool, heating each joint no longer than needed so that pads and tracks do not lift.
- Fit parts of the same capacitance and the same or higher voltage, with the polarity matching the board.
- On the drive, do not turn it over while the controller board is loose, or the write-protect pin can fall out.[5]
- Refit, connect a known-good supply, and check the self test (BREAK held at reset, then Q, A, Z, M, L and P) and a disk catalogue.[1]
Checks after recapping
[edit | edit source]- Measure +5 V, +12 V and −12 V at the board's power input.[3]
- Check the drive index period: 200 ± 5 ms (at TP9 on the drive board).[1]
- Check the TV picture and sound, and the audio output.
Related pages
[edit | edit source]- Sinclair ZX Spectrum +3
- Sinclair ZX Spectrum +3 General Maintenance
- Sinclair ZX Spectrum +3 Troubleshooting Guide
- Amstrad Spectrum +3 Service Manual
- Sinclair ZX Spectrum +2 Capacitor Replacement Guide
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Amstrad plc, Spectrum +3 Service Manual, hosted as File:Amstrad Spectrum +3 Service Manual.pdf; see Amstrad Spectrum +3 Service Manual. Electrical parts list, "Electrolytic Capacitors": 1uF/50V C13, 27, 38, 41 (part 20062); 100uF/16V C8, 29, 30 (part 20028), printed p. 20; main board circuit diagram with the notes on +3-only, +2A-only and Peritel-only parts, pp. 18–19; FD-1 EME-156 disk drive circuit diagram, p. 12.
- ↑ "ZX Spectrum Models", Spectrum for Everyone (retrieved 2026-10-19). The DC-DC converter circuit removed on the +2A/+3, with the rails fed directly from the power supply.
- ↑ 3.0 3.1 3.2 3.3 Guesser, ZX Spectrum +2A/+3 Schematic, redrawn, revision 20, 23 January 2020, zxnet.co.uk (retrieved 2026-10-19). C8 100 µF across the DC power input; C29 and C30 100 µF with C28 and C31 100 nF at the UHF modulator; C13 1 µF beside R3 and the reset circuit; C38 and C41 1 µF in the sound circuit; C48 1 µF deleted on the +3; C51 22 nF; C27 1 µF.
- ↑ "Factory fixes for Amstrad built Spectrums", zxnet.co.uk (retrieved 2026-10-19). Z70830 issue 1: R38 1.5 kΩ and C51 22 nF soldered on the copper side; D36, D37 and D38 at C41; C52 at IC5.
- ↑ 5.0 5.1 5.2 DataServe Retro, "Servicing the Sinclair ZX Spectrum +3 Disk Drive" (retrieved 2026-10-19). Several types of 3-inch drive in the +3, the EME-156 being by far the most common; the controller board held by three brass screws; the motor and stepper leads.