Acorn Archimedes A3000

Acorn Archimedes A3000

Acorn Archimedes A3000
Specifications
Manufacturer	Acorn Computers Ltd
Type	Home computer (keyboard-case)
Released	May 1989
Discontinued	1992
Intro price	£649 ex VAT; Acorn RGB monitor £200
CPU	ARM2 @ 8 MHz
Memory	1 MB RAM, official expansion to 2 MB
Storage	3.5" floppy drive, 1 MB unformatted (800 KB ADFS E); no internal hard disc option
Display	Analogue RGB (9-pin D), mono composite (phono); 640×256, up to 640×512 on a multiscan
Sound	8 voices, stereo with seven stereo positions; two built-in speakers
OS / Firmware	RISC OS 2.00
Predecessor	Acorn Archimedes A310
Successor	Acorn A3010, Acorn A3020
Model no.	AKB01

The Acorn Archimedes A3000 — sold as the BBC A3000 — was launched in May 1989, just before the A4x0/1 range, as Acorn phased out the 300 series. It put the Archimedes architecture into a single keyboard case at a home-computer price, and it was the last Acorn machine to carry the BBC logo on its keyboard and the "British Broadcasting Corporation Microcomputer System" label.

A standard A3000 cost £649 plus VAT at launch, with an Acorn RGB monitor a further £200.

Design

The A3000 is, in effect, an A310 in a smaller case with the MEMC1a in place of the MEMC1. Acorn cut cost by leaving out things rather than by changing the architecture:

• The serial port is not fitted as standard. The socket is on the back panel, but the interface components are an optional "serial upgrade"; machines without it carry a sticker above the socket saying so. Acorn's brochure lists the parallel port as standard "with provision for optional serial port".
• Expansion is one internal mini-podule and one external podule. There is no backplane and no four-slot expansion.
• There is no internal hard disc option at all. A hard disc on an A3000 means an external SCSI or IDE controller podule.

The board is a completely different layout from the 300-series machines and is far less crowded.

Chip set

Acorn's four custom chips carry internal codenames that appear on the parts themselves: Arabella (VIDC), Anna (MEMC) and Albion (IOC), alongside the ARM. Devices found on documented machines:

Function	Issue A board	Issue 3 board
ARM2	VL2333-QC	VL86C010-10QC
MEMC1a	VL2304A-QC	VL86C310-12QC
VIDC1a	VL2303A-QC (ARABELLA)	VL86C110-10QC
IOC	VL2311-QC	VL86C410-10QC
Floppy disc controller	VLSI VL1772-02PC
Keyboard controller	Intel 8051

Motherboard part numbers are 0280,000 Issue A and 0180,000 Issue 3. Acorn's service manual lists the design changes between Issue A and Issue 1 boards, which include a permanent 10 kΩ SMD resistor (R144) in place of a strapped-on part on the serial interface, added 22 Ω signal-conditioning resistors R141–R143 on REF8M, RA9 and IORQ, a 2n7 capacitor C116 added between SW3 and 0 V, link changes for genlocking and for JEDEC and non-JEDEC EPROMs, and added test points on the ARM and MEMC lines.

Acorn and the contemporary press both quote a typical execution rate of 4 MIPS. The measured figure on Chris Whytehead's Issue 3 A3000 under RISC OS 3.11 is 4.82 MIPS on ARMSi v4.0 and 4,728 Dhrystones per second — essentially identical to an ARM2 A310 with a MEMC1a at 4.80 MIPS. The MEMC1a does not make this machine meaningfully faster; its significance is that it will run at a higher memory clock, which is what the A540 and A5000 exploit. Claims of a 10–15% gain on the A3000 are not supported by measurement.

Memory

1 MB of DRAM as standard, in eight ICs mounted vertically above the ARM2, with an expansion connector above them. Acorn's official upgrade is a 1 MB RAM module that plugs into the main PCB, taking the machine to 2 MB — the figure both Acorn's service manual and its brochure give as the maximum. Third-party 1 MB modules such as Cumana's are commonly found; larger third-party upgrades exist but are outside Acorn's published specification.

RISC OS lives in 512 KB of ROM in four sockets. Links LK19 and LK20 select the ROM size (512K, 1M, 2M or 4M bit), and LK17/LK18 select JEDEC or non-JEDEC devices — set them wrong and the machine will not start.

Internal expansion

The internal mini-podule interface is configured as "Podule 1, Module 1" and connects via two 17-way 0.1-inch connectors plus two 5-way connectors (the latter fitted as standard from Issue 1 boards onwards). Cards should use 0.025-inch square pin headers.

Acorn's limits are worth knowing before fitting anything: maximum 600 mA from the +5 V rail, and maximum 0.5 W (100 mA) dissipation inside the case. Any upgrade must be able to drive at least 7 HCT and 3 TTL loads on the data bus.

The internal upgrades Acorn listed are the User Port / MIDI expansion card (AKA12), the 1 MB RAM upgrade, the serial port and the Econet module. The AKA12 carries a 65C22 VIA for the user port, a 2691 UART for MIDI, and a 27128 EPROM holding firmware and the podule ID byte 63.

Backup battery

The A3000 does not use a 3.6 V NiCd pack. Acorn's parts list gives B1: a NiCd 1.2 V 280 mAh cell, soldered directly to the PCB beside the RISC OS ROMs. It maintains the real-time clock and the battery-backed configuration RAM.

Acorn's own checks:

• LK6 is the non-volatile memory battery voltage test point: P1 is 0 V and P2 should read 1.2 V ± 0.2 V.
• If the NVM loses data and the real-time clock fails, check for about 1.1 V on IC6 pin 8 with the power off. If that voltage is not present, check R3 and R7. If it is below 1 V, change B1 and check D2 and C15.
• LK7 is the non-volatile memory clock test point: P1 0 V, P2 32.768 kHz.

Replacing B1 means desoldering it. Acorn's instruction is that repair sites without desoldering equipment and experience should not attempt it, because the board is easily damaged — and that care must be taken not to short the cell's terminals, even one being thrown away.

There is an unused battery compartment moulded into the base of the case, with its own screwed cover, to the right of the mouse socket. It corresponds to LK5 on the main PCB, which Acorn describes as a "connection point for an external battery (only used if supply of on board NiCad becomes a problem)". On a machine whose soldered cell has leaked, that compartment is the intended route to an external holder without further surgery.

Leaking NiCd cells are the defining long-term fault of Acorn machines of this era. See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Ports

From the rear, left to right: external expansion (a 96-pin connector taking a single standard Archimedes podule), analogue RGB (9-pin D), mono composite video (phono), headphone (3.5 mm, 32 Ω), parallel printer (25-way D, Centronics-compatible), serial (fitted only with the upgrade) and Econet (fitted only with the module). Neither a TV modulator nor a multisync-specific connector is provided, though a multiscan monitor on the RGB output gives up to 640 × 512.

The keyboard is Acorn's 103-key "enhanced PC" layout with a three-button mouse on a socket in the base of the case.

Sound

Acorn's brochure specifies two-channel stereo with seven stereo positions and eight voices, output to two built-in speakers or the 32 Ω headphone jack. The service manual's fault-finding for the speaker circuit gives a useful check: trace the audio through to Q11 and Q12, where the signal amplitude should be about 1.3 V peak to peak.

Replacement

Acorn replaced the A3000 range in 1992 with the A3010 for the home market and the A3020 for education, both built on the 12 MHz ARM250 and shipping with RISC OS 3. Prices for the new range started at £424.68 ex VAT (£499 inc VAT) for the A3010 "Family Solution".

Maintenance and repair

Main article: Acorn Archimedes A3000 Maintenance Guide

The priority job is B1. Remove the soldered NiCd cell and inspect the board around it before applying power to a machine that has been stored. Acorn's own note on one of its faulty A3000s is that corrosion at the bottom-left corner of the board — the battery corner — may be why it does not work.

See also Acorn Archimedes A3000 Troubleshooting Guide, Acorn Archimedes A3000 Capacitor Guide, Floppy Drive Repair and Recommended Tools. Acorn's full component-level fault-finding, links table and parts list are in the Acorn A3000 Service Manual hosted here, and the hardware reference is the Acorn A3000 Technical Reference Manual.

See also

• Acorn Archimedes A310 — the machine the A3000 condenses
• Acorn A3010 and Acorn A3020 — the 1992 replacements
• Acorn Archimedes A5000 — the ARM3 machine of the same period
• Acorn A3000 Service Manual