Acorn Archimedes A3020

Acorn Archimedes A3020

Acorn Archimedes A3020 with colour monitor
Specifications
Manufacturer	Acorn Computers Ltd
Type	Personal computer (education)
Released	September 1992
Discontinued	1995
Intro price	From £749 ex VAT (2 MB, floppy) with monitor
CPU	ARM250 @ 12 MHz
Memory	2 MB RAM (expandable to 4 MB)
Storage	3.5" floppy (1.6 MB); optional 2.5" IDE hard disc
Display	Analogue RGB, 15-pin VGA-type connector
Sound	8-channel, 8-bit logarithmic (VIDC1a)
Dimensions	479 mm × 267 mm × 73 mm
Weight	approx. 4 kg
OS / Firmware	RISC OS 3.11
Predecessor	Acorn Archimedes A3000
Successor	Acorn A7000
Codename	Heron E
Model no.	AGB22, AGB23, AGB33

The Acorn Archimedes A3020 is an all-in-one 32-bit computer that Acorn Computers announced in August 1992 and shipped from September 1992. It was the education member of a three-machine range built around the ARM250 processor, sold alongside the home-market A3010 and the three-box A4000.

The A3020 replaced the A3000 in schools. It kept the A3000's integrated-keyboard format but added a faster processor, an on-board IDE interface for a fitted hard disc, and a dedicated network socket for classroom use.

Positioning

Acorn aimed the A3020 at primary and middle schools. It shipped in the traditional BBC-beige case with red function keys, and every unit carried an on-board IDE controller so that a machine could be supplied floppy-only or with an internal hard disc. A rear network socket allowed the A3020 to work peer-to-peer or as a station on a client/server network without using the internal expansion slot.

Launch prices, quoted with a colour monitor and excluding VAT, were £749 for the 2 MB floppy-only model and £899 for the 2 MB machine with a 60 MB hard disc.

Processor

The A3020 uses the ARM250 clocked at 12 MHz. The ARM250 was Acorn's first ARM system-on-chip: it integrates onto one die the four devices that were separate on the A3000 — an ARM2-class processor core, the MEMC1a memory controller, the VIDC1a video and sound controller, and the IOC input/output controller. The core is cacheless (ARM2-class), so the A3020 delivers roughly 7 MIPS — about the same as the A3000's discrete chipset would at 12 MHz, but well short of the ARM3-based A5000.

Running the memory at 12 MHz with 80 ns DRAM, against the A3000's 8 MHz and 125 ns parts, gives the machine its performance step over its predecessor. A Chips & Technologies 82C711 peripheral controller provides the IDE, floppy, serial and parallel interfaces in a single support chip.

Memory and firmware

The A3020 ships with 2 MB of RAM and accepts a 2 MB upgrade board fitted into the on-board ZIP DRAM sockets, reached through a hole in the RF shield, for a 4 MB maximum. RISC OS is held in 2 MB of ROM (two devices); production machines carry RISC OS 3.11, with some early units on 3.10.

Storage

The floppy drive is a 3.5-inch high-density unit, formatted to 1.6 MB under the ADFS "F" format and driven by the 82C711. The on-board IDE interface, terminating at connector PL1, supports one internal 2.5-inch drive; launch machines used a 60 MB unit, and an 80 MB education variant followed. This on-board IDE is one of the main differences from the A3000, which had no built-in hard-disc support.

Ports and expansion

The rear panel carries, from left to right, a parallel printer port, a serial port, a network socket, a mouse port, a headphone socket and the analogue RGB video output, with the power switch at the right. The video connector is a 15-pin VGA-style socket carrying analogue RGB, the same connector used by the A5000; the A3020 has no TV modulator.

Internally the machine has one mini-podule expansion slot, mechanically compatible with A3000 upgrade cards, plus a separate network-interface slot that takes an Econet or Ethernet module and feeds the rear network socket. Econet is not fitted as standard. The A3020 has no joystick ports; the network connector occupies the position used for the joystick ports on the A3010.

Case and power

The A3020 is a single-box machine with the computer built into a sloping keyboard case, roughly 479 × 267 mm and 73 mm high, weighing about 4 kg. The mains power supply is built onto the main PCB rather than being a removable module, and the service documentation records two supply rails, +5 V and +12 V; the +12 V rail also appears on pin 12 of the video connector for SCART switching.

Differences from the A3010 and A4000

All three 1992 machines share essentially the same main-board design. The A3020 differs from its siblings as follows:

Feature	A3020 (education)	A3010 (home)	A4000 (professional)
Case	Single box, beige, red keys	Single box, grey, green keys	Three box, separate keyboard
Hard disc	On-board IDE, optional 2.5" drive	None fitted	On-board IDE, 3.5" drive standard
Network socket	Yes	No	Yes
TV modulator	No	Yes	No
Joystick ports	No	Two (9-pin)	No
RAM as sold	2 MB	1 MB (base)	2 MB

Sources: Chris's Acorns and Wikipedia.

Circuit diagrams and PCB

The A3020 main board is part 0194,500, codenamed "Heron E". Acorn documented the machine at module level in the Service Manual; the component-level circuit diagrams are in the Technical Reference Manual, both hosted on this wiki.

Main PCB	Circuit diagram (sheet 1 of 3)
Circuit diagram (sheet 2 of 3)	Circuit diagram (sheet 3 of 3)
PCB assembly (designators)

Discontinuation

Acorn ceased A3020 production in 1995, with remaining stock sold into 1996; the machine did not conform to newly introduced European electrical regulations. Its role passed to the Acorn A7000.

General maintenance

Main article: Acorn Archimedes A3020 Maintenance Guide

The dominant maintenance job on any surviving A3020 is dealing with the soldered NiCd backup battery, which leaks and corrodes the board around it. The on-board mains PSU and the ageing 2.5-inch hard disc are the other priorities. See the Acorn Archimedes A3020 Maintenance Guide.

Troubleshooting

Main article: Acorn Archimedes A3020 Troubleshooting Guide

Most faults trace to battery corrosion, the on-board PSU, or a monitor-type mismatch that produces no picture on an otherwise healthy machine. Because the ARM250 integrates the processor, memory, video and I/O controllers, a fault inside it is a whole-device replacement. See the Acorn Archimedes A3020 Troubleshooting Guide.

Capacitor guide

Main article: Acorn Archimedes A3020 Capacitor Guide

The A3020 board is mostly leaded electrolytics with a small number of surface-mount aluminium electrolytics, and is not a routine "recap" machine; the battery, not the capacitors, is the usual source of corrosion. See the Acorn Archimedes A3020 Capacitor Guide.

See also

• Acorn Archimedes A3010 — home-market sibling
• Acorn Archimedes A4000 — three-box sibling
• Acorn Archimedes A3000 — predecessor
• Acorn Archimedes A5000 — ARM3 flagship of the same era