Acorn Archimedes A3020

Acorn Archimedes A3020

A3020 with an Acorn colour monitor
Specifications
Manufacturer	Acorn Computers
Type	Personal computer (education)
Released	September 1992
Intro price	£880.08 including VAT (2 MB, floppy, with monitor); £1,056.33 with a 60 MB hard disc
CPU	ARM250 at 12 MHz
Memory	2 MB, expandable to 4 MB
Storage	3.5-inch floppy drive; optional internal 2.5-inch IDE hard disc
Display	Analogue RGB, 15-way mini D-type
Sound	Stereo; internal speaker and headphone socket
ROM	2 MB (RISC OS 3)
Power	12.5 W supply on the main board
OS / Firmware	RISC OS 3.10 or 3.11
Predecessor	Acorn Archimedes A3000
Model no.	AGB22 (floppy), AGB23 (60 MB hard disc), AGB33 (80 MB hard disc)

The Acorn Archimedes A3020 is a computer for schools that Acorn Computers announced in August 1992 and sold from September 1992. Like the A3000 it replaced, it has the keyboard, main board, supply and floppy drive in one case. It uses the ARM250, which combines the ARM2 processor with the MEMC1a, VIDC1a and IOC functions in one chip, and adds an IDE interface for an internal hard disc and a socket for an Econet or Ethernet network card. Its siblings are the home A3010 and the A4000.

History

Acorn's announcement described the A3020 as designed for education, particularly primary schools, with a cream case and red function keys. It came with 2 MB of RAM, upgradeable to 4 MB, and had network interface sockets and hard disc support built onto the board, so that a network card and hard disc could be fitted without using the internal expansion slot. The range went up to £899 for an A3020 with a 60 MB hard disc and a colour monitor. Including VAT, the A3020 cost £880.08 with 2 MB, a colour monitor and no hard disc, and £1,056.33 with a 60 MB hard disc.

Production of the A3020 and A4000 ended in 1995, with stock sold through 1996, because the machines did not meet newly introduced European electrical and electronics regulations. The A7000 then became Acorn's entry-level desktop.

Specifications

Acorn's feature table compares the three ARM250 machines:

A3010, A3020 and A4000 compared (Technical Reference Manual p. 1-1)

Feature	A3010	A3020	A4000
Design	Single box	Single box	Twin box
Processor	12 MHz ARM250	12 MHz ARM250	12 MHz ARM250
Base memory	1 MB	2 MB	2 MB
Expandable to	2 or 4 MB	4 MB	4 MB
Operating system	RISC OS 3, 2 MB ROM	RISC OS 3, 2 MB ROM	RISC OS 3, 2 MB ROM
Hard disc	None	Optional internal 2.5-inch IDE	Optional internal 3.5-inch IDE
Keyboard	103 keys, integral	103 keys, integral	103 keys, separate
Power supply	10 W	12.5 W	24 W
Colour TV modulator	Yes	No	No
Internal network expansion	No	Yes	Yes
Switched joystick inputs	2	No	No
Rechargeable clock battery	Yes	Yes	Yes

Chris Whytehead's two A3020s measured 7.18 and 7.09 MIPS on ARMSi 4.0.

Hardware

Main board

The A3020 main board is part 0194,500 (bare board 0294,500); Acorn's circuit diagram for it is titled "Heron 'E' Main PCB". Its main parts are the ARM250 (IC13), four 256K × 16 DRAMs (IC21, IC22, IC31, IC32) with four unfitted positions (IC33-IC36) for the memory upgrade, two RISC OS ROMs (IC17, IC18), an 82C711 peripheral controller (IC24), the keyboard controller (IC2), an 8583 clock and CMOS RAM chip (IC5), an LM386 speaker amplifier (IC10) and the plug-in audio hybrid module (IM2, part 0194,007).

Acorn's Appendix D notes that initial production of all three machines used a main board carrying a daughter card with a discrete-component version of the ARM250, clocked by 36 MHz and 24 MHz oscillators instead of the single 72 MHz oscillator used with the ARM250 chip. The daughter card's parts list is headed "A3020/A3010 CPU module".

Memory

The DRAM size is set by links LK31 and LK32: 1-2 and 2-3 for 2 MB, 2-3 and 1-2 for 4 MB. The upgrade sockets are reached through a hole in the metal shield, which should have a cover. Chris Whytehead's second machine has an IFEL ZA1 upgrade in those sockets.

Storage

The IDE interface is on the board, with a 44-way connector (PL10) for a 2.5-inch drive. The AGB23 had a 60 MB Conner drive as standard and the AGB33 an 80 MB drive; the AGB22 had no hard disc. The floppy drive is a 3.5-inch unit using the A5000's 1.6 MB format.

Power supply

The supply is part of the main board. A 25 VA mains transformer (L1, part 0194,512) feeds a rectifier and an L4974 step-down switching regulator (IC38) for the 5 V rail, a 78L12 (Q1) for the regulated 12 V used by the SCART interface and the audio hybrid, and a centre-tapped second winding for unregulated ±12 V at 50 mA for the RS232 circuits. The transformer contains a thermal fuse that must not be bypassed; if it fails, the transformer is replaced. The A3020 uses the higher-rated L4974 where the A3010 uses an L4960; otherwise the two supplies are the same design.

The board fuses are FS1 (250 mA T, 20 × 5 mm), FS2, FS3 and FS5 (250 mA F, surface-mount) and FS4 (50/63 mA, axial). The network expansion allowance is 300 mA internal plus 150 mA external.

Backup battery

The clock and CMOS RAM are backed by BT2, a 1.2 V 280 mAh nickel cell soldered to the board (Acorn part 0817,014, "BAT NI 1V2 280MAH VT PCB"). It is at the top right of the board, above the floppy drive connector.

Ports and expansion

From left to right on the rear panel: parallel, RS232 serial, network (fitted only with a network card), mouse, headphones and analogue RGB, with the power switch at the far right. A mini-podule can be fitted behind a blanking plate above the ports. The video output is a 15-way mini D-type socket, with the same pin-out as the A5000's. The network card fits a separate internal slot, described in Acorn's network interface specification.

Known faults

• Battery leakage from BT2 onto the board around it. See the Acorn Archimedes A3020 Maintenance Guide.
• The hard disc in hard-disc models is now over thirty years old. See Hard Drive Maintenance and Repair.
• Crackling sound. On the related A3010 and A4000, Stardot members traced crackle to broken pins on the audio hybrid module, which the A3020 shares (IM2, 0194,007).

The capacitor list is on the Acorn Archimedes A3020 Capacitor Guide.

Documentation

• Acorn A3010, A3020 and A4000 Service Manual: Acorn's module-level service manual, part 0494,059, with fault-finding flowcharts, the power-on self-test codes, disassembly and the dealer test disc procedures.
• Acorn A3010, A3020 and A4000 Technical Reference Manual: system description, power supply, links, connectors and full parts lists for every board.
• Main PCB circuit diagram: sheet 1, sheet 2 and sheet 3, and the PCB assembly drawing.

Gallery

• 
  A3020 main board 0194,500
• 
  Main PCB assembly drawing
• 
  Main PCB circuit diagram, sheet 1
• 
  Main PCB circuit diagram, sheet 2
• 
  Main PCB circuit diagram, sheet 3

Related pages

• Acorn Archimedes A3020 Maintenance Guide
• Acorn Archimedes A3020 Troubleshooting Guide
• Acorn Archimedes A3020 Capacitor Guide
• Acorn Archimedes A3010 and Acorn Archimedes A4000
• Acorn Archimedes A3000