Sinclair QL

Sinclair QL

Sinclair QL (Quantum Leap), 1984
Specifications
Manufacturer	Sinclair Research Ltd
Type	Personal computer
Released	12 January 1984 (announced); first deliveries April 1984
Discontinued	1986
Intro price	£399 (1984)
CPU	Motorola 68008 @ 7.5 MHz
Memory	128 KB RAM (officially expandable to 640 KB)
Storage	Two built-in Microdrive tape-loop cartridge drives
Display	512×256 (4 colours) or 256×256 (8 colours + flash)
Sound	Single-channel, generated by the 8049 IPC
Dimensions	47 cm × 14 cm × 5 cm
Weight	1.4 kg
OS / Firmware	QDOS with SuperBASIC in 48 KB ROM
Predecessor	Sinclair ZX Spectrum
Successor	None (line discontinued)
Codename	ZX83
Model no.	Build standards D02–D18, S13, SG18

The Sinclair QL (for Quantum Leap) is a personal computer that Sinclair Research Ltd announced on 12 January 1984 as an upper-end counterpart to the ZX Spectrum, aimed at serious home users, professionals and small businesses. It was Sinclair's last desktop machine for that market and did not achieve commercial success.

The QL is built around a Motorola 68008 — a member of the 68000 family with 32-bit internal registers but an 8-bit external data bus — and runs QDOS, a pre-emptive multitasking operating system, with the SuperBASIC interpreter as its command line. The electronics were designed by David Karlin and the case by Rick Dickinson, who had styled the ZX81 and ZX Spectrum.

Launch and reception

The QL was announced before it was ready to build. At the launch there was no complete working prototype, yet Sinclair took orders immediately and promised delivery within 28 days; the first customer machines only began to trickle out in April 1984, which drew criticism and the attention of the Advertising Standards Authority.

Early production machines shipped with preliminary firmware full of bugs, and part of the operating system had to be carried on an external 16 KB ROM cartridge — known as the "kludge" or "dongle" — hanging out of the back of the machine, until the design was revised to hold the necessary 48 KB of ROM internally instead of the 32 KB originally specified.

BYTE reviewed the machine in September 1984 and called it a "premature baby", criticising the incomplete operating system, the "dead and unresponsive" keyboard, the fragile Microdrive tapes and SuperBASIC's slow execution, while approving of the bundled Psion applications.

UK production was suspended in 1985 for lack of demand, and the QL was officially discontinued after Amstrad acquired Sinclair's computer product lines in April 1986. Around 140,000 machines were built in total across roughly 20 build standards and 16 circuit-board issues.

Linus Torvalds owned a QL, and has said that the lack of software for it in Finland got him used to writing his own — a habit that fed into his later work on the Linux kernel.

Architecture

Sinclair QL system block diagram (Figure 1.3 of the QL Service Manual): the 68008 processor with the ZX8301 master chip, ZX8302 peripheral chip and 8049 IPC.

The machine is built from the 68008 plus three support devices:

Sinclair QL main devices

Device	Position	Function
Motorola 68008	IC18	CPU at 7.5 MHz; 32-bit internal registers, 8-bit external data bus
ZX8301 "Master Chip"	IC22	Video display generator and DRAM refresh; made by Plessey (CLA2310, later CLA2345)
ZX8302 "Peripheral Chip"	IC23	Microdrives, RS-232 transmit, QLAN network, real-time clock, link to the IPC; made by NCR
Intel 8049 IPC	IC24	Keyboard and joystick scanning, RS-232 receive and sound; licensed 8049 with custom Sinclair firmware, made by Philips or NEC
HAL	IC38	Address decode; added at Issue 6, replacing IC17 and IC27

The ZX8301 divides the 15 MHz master crystal (X1) by two and distributes the resulting clock around the board and to the expansion connector. Because the ZX8301 steals memory cycles to fetch the display, and the 68008's data bus is only 8 bits wide, the QL performs well below what its nominal clock speed suggests.

The 8049 was a late addition: the ZX8302 was originally intended to absorb its functions.

Memory and firmware

The QL has 128 KB of RAM as standard, officially expandable to 640 KB and in practice to 896 KB with third-party hardware. QDOS and SuperBASIC live in 48 KB of ROM.

At least 13 ROM releases exist. The version can be read on a running machine with PRINT VER$:

Principal QL ROM versions

VER$	QDOS	Notes
FB, FB.2	1.0x	Earliest; EPROM only, used with the external "kludge" cartridge
PM	1.02	EPROM, dongle
AH	1.02	First masked ROMs
JM	1.03	The common UK version
JS	1.10	Later UK version, fewer bugs
JSU	1.10	Samsung-built US machines
MGx	1G13	Samsung-built German machines

Community-developed replacements followed, most notably Minerva, a rewritten QDOS offering better speed and full support for the second frame buffer, and later Tony Tebby's SMSQ/E.

Video

The ZX8301 reads a 32 KB frame buffer in main RAM and generates five signals — red, green, blue, composite sync (CSYNCL) and vertical sync (VSYNCH) — which are routed to the 8-pin DIN monitor socket J7. The same RGB and sync signals also feed IC28, which produces composite PAL for the internal UHF modulator M1, and are mixed in transistor TR9 to give a composite monochrome output.

Two display modes are available:

• Mode 4 — 512 × 256 pixels in four colours (black, red, green, white)
• Mode 8 — 256 × 256 pixels in eight colours with per-pixel flashing

The hardware can switch between two frame buffers for double buffering, but the original firmware does not use it; Minerva does.

The QL outputs 312 lines at 50.08 Hz with a 15.62 kHz line frequency, and overscans horizontally by roughly 24 pixels each side of the TV-safe area. This is reported to be because the ZX8301's timing constants were chosen for the flat-screen CRT originally planned for the machine, and it is why Mode 4's 85-character display needs a monitor rather than a domestic television. At power-on the machine asks the user to choose with F1 (monitor, Mode 4) or F2 (television, Mode 8).

Ports and connectors

Sinclair QL rear panel. UK machines use BT-style telephone connectors for the serial and joystick ports; Samsung-built export machines use DE-9 sockets instead.

Sinclair QL connectors (Service Manual designations)

Ref	Connector	Purpose
J1	64-way Viking Eurocard	Main expansion bus
J2	30-way edge connector	ROM cartridge slot
J3, J4	BT 603A LH (type 630W)	Joystick / control ports CTL1, CTL2
J5, J6	BT 603A RH (type 631W)	Serial ports SER1, SER2 (RS-232C)
J7	8-pin DIN	RGB monitor output
J8	3-pin socket	Power input from the external supply
J9, J10	3.5 mm jack, single pole	QLAN network
J11, J12	9-way and 11-way flex	Keyboard membrane tails

Connector data is from the Service Manual parts list. Samsung-built machines for the US and German markets replace the BT-style serial and joystick connectors with DE-9 sockets.

Power supply

The QL is powered by an external, custom power pack supplying 9 V DC at 2 A and 44 V peak-to-peak AC into connector J8. The pack uses a thyristor to limit peak voltages on the DC output but is otherwise unregulated and has significant ripple.

On the board, the AC feed is rectified and regulated by IC37 (78L12) and IC36 (79L12) to give +12 V at 80 mA and −12 V at 50 mA, while the DC feed is regulated to +5 V by IC35, a 7805 mounted on the large heatsink beside the Microdrives. All three regulators have thermal and short-circuit shutdown.

Microdrives

The two Microdrive slots, MDV1 and MDV2.

In place of floppy drives the QL has two built-in Microdrives, using a continuous-loop tape cartridge first introduced for the ZX Spectrum in 1983, though the QL uses a different logical format. A formatted cartridge holds a little over 200 sectors of 512 bytes.

Microdrive reliability was one of the QL's most damaging problems at launch. It improved with later production — particularly the Samsung-built machines — and with aftermarket work by firms such as Adman Services and TF Services, but too late to undo the reputation. Microdrive cartridges were also the only distribution medium available to QL software publishers, and cost over six times as much to produce as a compact cassette, which discouraged support for the platform.

Detailed servicing information is on the separate Sinclair QL Microdrive Troubleshooting Guide.

Build standards and board issues

Machines carry a build standard and serial number on a label on the underside, in the form Dxx-yyyyyy (Datatech) or S*xx-yyyyyy (Samsung).

• D — (THORN EMI) Datatech, the UK manufacturer. Build standards D02 to D18; at least 121,821 machines.
• S13 — Samsung, North American market; 4,861 machines.
• SG18 — Samsung, German market; 9,800 machines.

UK boards ran through issues ZX-83 ISS.2, ISS.4, ISS.5, ISS.6 and ISS.7; Samsung boards are numbered US3 through US6. The most significant change is at Issue 6 (autumn 1984, build standard D14), which introduced the HAL at IC38, removed IC17 and IC27, added resistors R102–R104 and replaced the trimmer TC1 with a fixed 22 pF capacitor C53.

Samsung machines have the case interior silver-coated and other changes for FCC and VDE compliance, including diodes fitted piggyback on the ZX8301's RGB video output pins — a factory acknowledgement of the video-output fragility discussed in the troubleshooting guide.

Circuit diagrams and PCB

Main board	Circuit diagram (Issue 5)
Circuit diagram (Issue 6)	PCB component layout (Issue 5)
PCB component layout (Issue 6)	Power supply pinout

Software

QDOS was primarily designed by Tony Tebby, with SuperBASIC written by Jan Jones. The machine was bundled with a Psion office suite — Quill (word processor), Abacus (spreadsheet), Archive (database) and Easel (business graphics). Only around 70 games were ever released for the QL, against more than 4,700 for the ZX Spectrum, which was one reason Spectrum owners saw little reason to upgrade.

Related machines

The QL's CPU, ZX8301 and ZX8302 chips and Microdrives form the basis of the ICL One Per Desk, also sold as the British Telecom Merlin Tonto and the Telecom Australia Computerphone. After Amstrad dropped the QL, CST produced the Thor range of compatibles, and Miracle Systems sold the Gold Card and Super Gold Card processor and memory upgrades.

General maintenance

Main article: Sinclair QL Maintenance Guide

The QL runs hot, its keyboard membrane is a known wear item, and the board itself needs careful handling. See the Sinclair QL Maintenance Guide.

Troubleshooting

Main article: Sinclair QL Troubleshooting Guide

The Service Manual documents a full power-on diagnostic sequence in which the screen colour and pattern identify the failing subsystem, along with test-point voltages and a symptom table. The RGB monitor output is a particular weak point. See the Sinclair QL Troubleshooting Guide.

Capacitor replacement

Main article: Sinclair QL Capacitor Replacement Guide

Sinclair published a complete component-level parts list for the QL, so every capacitor's designator, value and type is known. See the Sinclair QL Capacitor Replacement Guide.

See also

• Sinclair QL Microdrive Troubleshooting Guide
• Sinclair ZX Spectrum — the 8-bit machine the QL was intended to sit above
• Sinclair ZX81