Sinclair ZX Spectrum +2
 | |
| Sinclair ZX Spectrum +2 (1986), the grey Amstrad-built model | |
| Specifications | |
|---|---|
| Manufacturer | Amstrad (under the Sinclair brand) |
| Type | Home computer |
| Released | 1986 |
| Intro price | £149 (1986)[1] |
| CPU | Zilog Z80A at 3.5469 MHz |
| Memory | 128 KB RAM (8 × 16 KB banks) |
| Storage | Built-in "Datacorder" cassette deck |
| Display | 256×192 pixels, 32×24 characters, 15 colours |
| Sound | AY-3-8912A (3 channels) plus the ULA beeper |
| OS / Firmware | Sinclair BASIC (128 BASIC and 48 BASIC) in 32 KB ROM |
| Predecessor | Sinclair ZX Spectrum 128 |
| Successor | ZX Spectrum +2A (late 1988) |
| Model no. | Boards Z70500 Issue 3 and Z70700 Issue 1 |
The Sinclair ZX Spectrum +2 is a 128K home computer released in 1986 for £149. It was Amstrad's first Spectrum, following its purchase of the Spectrum range and the Sinclair brand that year, and has a grey case, a spring-loaded keyboard, two joystick ports and a built-in cassette recorder called the "Datacorder". The start-up message reads "© 1986 Amstrad".[1]
Functionally the +2 is a repackaged Spectrum 128. According to Spectrum for Everyone, Amstrad engineers reverse-engineered a Sinclair 128 in a hurry to have the machine on sale for Christmas 1986, starting before the purchase of Sinclair had formally completed.[2]
What Amstrad changed
[edit | edit source]Compared with the Spectrum 128 "Toastrack", the +2 adds:[2][1]
- A built-in Datacorder cassette deck in place of an external tape recorder.
- Two joystick ports with the Sinclair pinout, driven by an Amstrad 40057, which Spectrum for Everyone describes as essentially the MT62001 used in the ZX Interface 2.
- A full-size grey case with a spring-loaded keyboard.
The Z80A, the ULA, the 128 KB of banked RAM, the AY-3-8912A sound chip and the 32 KB ROM are carried over from the 128.[2]
Board revisions
[edit | edit source]Two boards were used in the grey +2:[2]
| Board | Notes |
|---|---|
| Z70500 Issue 3 | Built in Taiwan by Amstrad's contract manufacturer, Orion. Uses the Amstrad 40058. A slightly later version marked "0500 Issue 3" has very minor layout changes and no functional difference. |
| Z70700 Issue 1 | The UK-built board. Functionally identical to the Z70500, but uses mostly axial capacitors and other UK-sourced parts, with a PCF1306P where the Z70500 has the Amstrad 40058. Spectrum for Everyone suggests it was made to use up parts Amstrad inherited from Sinclair's suppliers. |
Spectrum for Everyone describes the PCB quality on the Amstrad-produced boards as poor, needing great care when replacing components to avoid lifting pads or tracks.[2] The soldering notes are on the Sinclair ZX Spectrum +2 General Maintenance page.
Architecture
[edit | edit source]| Device | Function |
|---|---|
| Zilog Z80A | CPU, clocked at 3.5469 MHz (the Spectrum 128 figure). The 128 has a 17.734475 MHz crystal; Amstrad's +2 parts list gives X1 as 35.4690 MHz[5] |
| ULA (IC14) | Video, keyboard scan, tape interface and beeper. Amstrad's parts list gives IC14 as "ULA7K010E5/AMS40056": the Ferranti 7K010 used in the Spectrum 128, or Amstrad's 40056 in its place; see Sinclair ZX Spectrum 128 ULA[6] |
| AY-3-8912A | Three sound channels in addition to the ULA beeper; also handles the bit-banged serial interface |
| TEA2000 | Colour encoder |
| Amstrad 40057 | Dual joystick port interface |
| 128 KB DRAM | Eight 16 KB banks, paged into the Z80's address space |
Many diagnostic tools report RAM faults using 48K Spectrum IC numbers. On the +2 the upper set, IC17–IC24, corresponds to IC15–IC22 on a 48K Spectrum, and the lower set, IC25–IC32, corresponds to IC13–IC6, in reverse order.[3]
As on all the 128K machines, the mix of the AY's three channels and the ULA beeper is not well balanced, and ULA sounds are usually much louder.[3]
On the 128 and the grey +2, RAM banks 1, 3, 5 and 7 are contended and banks 0, 2, 4 and 6 are not, although the official 128 specification said otherwise. The later +2A and +3 follow the specification, so some software written on the real 128 or grey +2 runs differently on them, most obviously as distorted beeper sound or sampled speech.[2]
Power supply
[edit | edit source]The +2 takes an external unregulated supply through a 2.1 mm barrel connector, like the 128.[2] The Spectrum 128 Service Manual describes the on-board supply: a 7805 regulator gives +5 V for the logic, the ULA and the sound and UHF modulators, and an inverter around TR4 and TR5 raises the 9 V input above +12 V. D15 and C44 rectify and smooth the inverter output to +12 V, which feeds the RS232 driver IC33 and the keypad; a charge pump (C111, C112, D28 and D29) gives −12 V for IC33, and zener D19 derives −5 V for the expansion port from that rail.[4] Tynemouth Software identifies the inverter transistors on a grey +2 as a ZTX650 and a ZTX213.[3]
A working +2 draws between about 800 mA and 1.2 A depending on the type of RAM fitted, so Tynemouth Software tests boards on a bench supply current-limited to 1.5 A.[3]
Documentation
[edit | edit source]Amstrad issued a 12-page Spectrum +2 Service Manual, hosted here, covering the specification, power adaptor safety tests, a fault-finding flow chart, cassette and software analysis, the test software, the electrical parts list, the circuit diagram, the PCB layouts, the tape interface board and the cassette mechanism and cabinet parts lists.[7] The Sinclair ZX Spectrum 128 Service Manual covers the same architecture at component level, with the 128's digital and analogue schematics in its appendices (sections 6.2 and 6.3).[4]
How the +2A and +2B differ
[edit | edit source]The black +2A (sold from late 1988) and the +2B are built on the +3's circuit board,[1] so repair information for the grey +2 does not carry across. Spectrum for Everyone lists the main differences:[2]
- They use the Z70830 board (shared with the +3, with the floppy-drive parts not fitted) or the Z70833, a cut-down board without the floppy area.
- Most of the ULA, logic, PCF and 40057 functions are combined in one gate array, the Amstrad 40077.
- The DC-DC converter is removed. The rails come from a new power supply with a 6-pin DIN connector instead of the 2.1 mm barrel connector, so grey +2 and +2A power supplies are not interchangeable.
- The RAM changes from sixteen 64 Kbit × 1 chips to four 64 Kbit × 4 chips.
- The split bus is implemented inside the gate array, so external peripherals can no longer drive the keyboard.
- RAM contention follows the original 128 specification.
- The Z70830's audio circuit has a design error that distorts the output heavily; it is mostly corrected on the Z70833.
General maintenance
[edit | edit source]The Datacorder belts and head, the PCB, the keyboard and the power supply are covered in the Sinclair ZX Spectrum +2 General Maintenance guide.
Troubleshooting
[edit | edit source]See the Sinclair ZX Spectrum +2 Troubleshooting Guide.
Capacitor replacement
[edit | edit source]See the Sinclair ZX Spectrum +2 Capacitor Replacement Guide.
See also
[edit | edit source]- Sinclair ZX Spectrum+, the 1984 48K machine
- Sinclair ZX Spectrum, the original
- Sinclair ZX Spectrum Keyboard Membrane Repair
- Sinclair ZX Spectrum 128 ULA, the Ferranti 7K010 used in the 128 and the +2
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 "ZX Spectrum", Wikipedia. Source for the launch, the price, the "© 1986 Amstrad" start-up message and the later +2A.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 "ZX Spectrum Models", Spectrum for Everyone. Source for the Z70500 and Z70700 boards, the reverse-engineering account, the Amstrad 40057, RAM contention, the PCB quality warning and the +2A/+3 boards.
- ↑ 3.0 3.1 3.2 3.3 3.4 Tynemouth Software, "Spectrum 128K +2 Grey Repairs", June 2017. Source for the RAM IC mapping, the AY, TEA2000 and 40057 roles, the sound balance, the ZTX650/ZTX213 inverter and the current draw.
- ↑ 4.0 4.1 4.2 Sinclair ZX Spectrum 128 Service Manual (File:ZX Spectrum 128 Service Manual.pdf), Sinclair Research Ltd; re-typeset Revision 1.1 by Brendan Alford. Section 1.10 (power supplies) and the basic-checks table (crystal and CPU clock frequencies).
- ↑ Amstrad Consumer Electronics plc, Spectrum +2 Service Manual, electrical parts list, "Miscellaneous" (p. 5): X1, crystal 35.4690 MHz, Amstrad part 172067. Hosted as File:Amstrad Spectrum +2 Service Manual.pdf.
- ↑ Amstrad Consumer Electronics plc, Spectrum +2 Service Manual, hosted as File:Amstrad Spectrum +2 Service Manual.pdf: electrical parts list (p. 5), "I.C. 14, IC. ULA7K010E5/AMS40056", part no. 172046; circuit diagram (pp. 6 and 7), the ULA's pin connections and the 74F74 (IC13) that divides the 35.4690 MHz oscillator to give the "17M" clock on ULA pin 1.
- ↑ Amstrad Consumer Electronics plc, Spectrum +2 Service Manual, 12 pages, hosted as File:Amstrad Spectrum +2 Service Manual.pdf: contents (p. 2), flow chart (p. 3), test software and RAM colour table (p. 4), electrical parts list (p. 5), circuit diagram (pp. 6–7), PCB and component layouts of main board Z70500 Issue 3 (pp. 8–9), tape interface PCB Z70501 (p. 10).