Acorn Archimedes A5000

Acorn Archimedes A5000

Acorn Archimedes A5000
Specifications
Manufacturer	Acorn Computers Ltd
Type	Personal computer (three-box desktop)
Released	September 1991; 33 MHz "Alpha" revision September 1993
Discontinued	1994
Intro price	£999 ex VAT (1 MB, floppy only); £1,499 ex VAT (2 MB, 40 MB hard disc, with Acorn 14" multiscan monitor)
CPU	ARM3 @ 25 MHz; 33 MHz on the 1993 Alpha revision
Memory	1, 2 or 4 MB; 4 MB is the limit of the single MEMC1a, 8 MB with a third-party dual-MEMC upgrade
Storage	3.5" floppy (1.6 MB ADFS F, reads 1.44 MB DOS); on-board IDE hard disc, 40 MB upwards
Display	VIDC1a; 15-pin VGA-type analogue RGB connector
Sound	8-channel, 8-bit logarithmic (VIDC1a)
OS / Firmware	RISC OS 3.00, later 3.10 and 3.11
Predecessor	Acorn Archimedes A540
Successor	Acorn Risc PC 600
Model no.	ALB10–ALB55, ALC10, ALC20

The Acorn Archimedes A5000 was launched in September 1991. It was the first Acorn computer to ship with RISC OS 3, and it moved the Archimedes onto industry-standard interfaces: a PC-style 15-pin VGA monitor connector, a PC-standard serial port, a bi-directional parallel port, a high-density floppy drive and an on-board IDE controller in place of the ageing ST506/MFM interface.

Acorn's launch prices, ex VAT, were £999 for the 1 MB floppy-only model and £1,499 for the 2 MB model with a 40 MB hard disc and an Acorn 14-inch multiscan monitor. The £1,499 figure is a system price including the monitor, not a bare machine.

What changed from the A400 series

Acorn and Chris Whytehead both list the same five changes, and they are the reason an A5000 feels like a different generation from an A420/1:

• A PC-standard 15-pin VGA monitor connector in place of the 9-pin RGB socket of the Archimedes and A3000 ranges, so an ordinary PC monitor works.
• A PC-standard serial connection in place of RS423.
• A bi-directional parallel port.
• A floppy drive handling 3.5-inch high-density discs, with a new Acorn 1.6 MB F format, and reading MS-DOS discs up to 1.44 MB with the operating system detecting the format automatically.
• An on-board IDE controller replacing the ST506/MFM controller.

The ARM3 also runs against a 12 MHz memory clock rather than the 8 MHz of the A300, A400 and A400/1 machines.

Models

Acorn shipped a long list of variants.

Code	Configuration
ALB10	1 MB, floppy only
ALB12	2 MB, 40 MB hard disc
ALB14	4 MB, 40 MB hard disc
ALB22	2 MB, 80 MB hard disc
ALB24	4 MB, 120 MB hard disc
ALB25	4 MB, 162 MB hard disc
ALB27 / ALB28	A5000 NS (Network System) and A5000 ES (Econet System) — disc-less network stations
ALB32	2 MB, 80 MB hard disc, 33 MHz ARM3 (Alpha)
ALB35	4 MB, 160 MB hard disc, 33 MHz ARM3 (Alpha)
ALB53 / ALB55	2 MB and 4 MB, 210 MB hard disc
ALC10 / ALC20	2 MB Learning Curve, 40 MB and 80 MB hard disc

Acorn's own final assembly parts list for the standard machine specifies a 2 MB main PCB, a 40 MB 3.5-inch IDE drive, a 4-way backplane (part 0192,004), a "Brisbane" 240 V PSU and a 3.5-inch floppy drive.

Video

The A5000 uses the VIDC1a, the same video and sound controller as the rest of the Archimedes range; documented machines from both 1991 and 1993 carry the VL2303A part. No A5000 shipped with a VIDC20 — that chip first appeared in the Risc PC of 1994. Any specification claiming VIDC20 or VRAM on an A5000 is wrong.

What the A5000 does have is the VGA-type connector, which is what lets it drive a standard PC or multiscan monitor. Graphics accelerator podules such as the State Machine G8 were sold to improve on VIDC1a's output.

Memory

The MEMC1a addresses a maximum of 4 MB, and that is the A5000's official ceiling. Memory is on the main PCB, expanded by a plug-in memory card — Atomwide's ALA20 4 MB card is the one usually found — not by industry-standard SIMMs.

Acorn's service manual documents the combinations through links LK23 and LK24, which must match the memory actually fitted or the machine will fail its memory test:

Total DRAM	On main PCB	On upgrade card	LK23	LK24
1 MB	1 MB	—	not connected	not connected
2 MB	2 MB	—	not connected	2–3
4 MB	4 MB	—	not connected	1–2
2 MB	1 MB	1 MB	not connected	2–3
4 MB	1 MB	3 MB	1–2	2–3
4 MB	2 MB	2 MB	1–2	2–3

Going beyond 4 MB needs a second MEMC1a. The September 1993 Alpha motherboard was changed to socket the MEMC1a specifically to make this practical: the upgrade replaces it with a plug-in daughterboard carrying two MEMC1a devices, one master and one slave, giving 8 MB. IFEL and Simtec both made one.

Processor

The 25 MHz ARM3 has 4 KB of cache. Chris Whytehead's 25 MHz A5000 with an FPA10 measures 13.75 MIPS on ARMSi v4.0 and 19,557 Dhrystones per second; his 33 MHz Alpha measures 17 MIPS and 22,809 Dhrystones per second.

The Alpha (September 1993)

Acorn refreshed the range in September 1993 with a 33 MHz ARM3 moved to a 0.8 µm process, claiming up to a third more performance and, in Acorn's words, measured performance "faster than a typical 33 MHz 486DX PC". Prices fell about 10% across the range, starting at £1,275.74 ex VAT for the 2 MB / 80 MB model and £1,445.96 for 4 MB / 160 MB, with the Econet and Ethernet network models at £1,175.74 and £1,275.74. Externally an Alpha is identical to an ordinary A5000 apart from a "33MHz" label between the keyboard and headphone sockets.

FPA10

The A5000 motherboard has a socket for the FPA10 floating point accelerator, which Acorn released in July 1993 at £99 ex VAT for the A5000, A540 and R260. Acorn's figures are 250 mW dissipation, up to 5 MFLOPS peak at 26 MHz and an average above 3 MFLOPS, with floating point performance under the RISC OS floating point emulator improving by as much as a factor of 50.

Peripheral controller

IDE, floppy, serial and parallel are handled by a single Chips & Technologies 82C710 peripheral combination controller — the part Acorn's own functional test names in its serial test ("Passed SERIAL, 82C710 CHIP TEST"). Several links depend on it: LK13 selects whether the parallel port interrupt comes from the ACK signal or from the 82C710's PINTR, LK21 connects pin 34 of floppy connector B to the 82C710's disc-change input, and LK17 selects normal or alternate write pre-compensation.

The IDE connector PL9 is a standard 40-way header carrying the full AT-mode signal set.

RISC OS 3

The A5000 was the first Acorn machine to come with RISC OS 3 installed, and the ROM grew from the 512 KB of RISC OS 2 to 2 MB. Acorn's launch claim was more than 300 enhancements over previous releases, with many applications, support modules and popular fonts moved into ROM, releasing up to 150 KB of extra user workspace.

The RISC OS 3.00 ADFSBuffers bug

This matters if you are using an original A5000. The first A5000 models — ALB10, ALB12 and ALB14 — shipped with RISC OS 3.00, which has a serious bug in its ADFSBuffers code that causes disc corruption. If you are running RISC OS 3.00, set ADFSBuffers to 0 to avoid it. Acorn issued RISC OS 3.10 as the fixed version and used it on subsequent machines; RISC OS 3.11 then replaced 3.10 and became the standard RISC OS 3 release.

Version dates seen in ROM on documented machines are 30 April 1992 for RISC OS 3.10 and 29 September 1992 for RISC OS 3.11. RISC OS 3.19 is the German localisation of 3.11.

The A5000/RISC OS 3 Release Note documents the differences from RISC OS 2 and the upgrade path, and includes Acorn's own list of known problems — among them that !Configure does not set the monitor type correctly for SuperVGA monitors, which must be set manually with *configure monitortype 4.

Expansion

Four podule slots on the 0192,004 backplane, fitted as standard. There is a fifth ROM socket on the main PCB whose purpose is unclear; link LK15 selects its device size, and it appears never to have been used in production.

Cards documented on surviving A5000s include the Acorn AKA10 BBC I/O podule, Cumana 16-bit SCSI, the State Machine G8 graphics accelerator and the Acorn ADF10 Econet interface.

Construction and known faults

Acorn's service manual states plainly that "surface mount technology is used on the printed circuit boards of the A5000 computer" and that component-level repairs should go to an Acorn Authorised Central Service Workshop. That construction is the source of the machine's defining long-term problem: the surface-mount aluminium electrolytic capacitors leak with age, corroding pads and tracks, and produce faults ranging from RAM-control errors and loss of sound to general instability. Recapping and cleaning the board is the main restoration job. Per-designator values are on the on-wiki Acorn A5000 Circuit Diagrams.

Acorn's service manual recognises three PSU failure modes — complete failure, individual rail failure, and thermal shutdown — and gives a separate diagnostic path for each. Mains voltage and stored charge are present in the supply; see Capacitor Failure Symptoms before working on it.

Backup battery

The A5000 does not use a Dallas DS1287 real-time clock module. The machine has a battery on the main PCB, visible next to the FPA10 socket in photographs of a documented board.

Acorn's A5000 module-level service manual does not identify the cell: it is a module-level document, it covers the battery-backed RAM test and tells the engineer to check the CMOS test data file on failure, but it gives no battery type or part number. No published Acorn figure for the A5000 cell has been found for this page, so none is stated here. For comparison, the machines either side of it in Acorn's range — the A3000 (B1) and the A540 (BT1) — both use a 1.2 V 280 mAh NiCd cell soldered to the PCB, per Acorn's own parts lists for those machines.

Practically: identify the cell on your own board before ordering a replacement, and remove it before applying power to a machine that has been stored. Acorn NiCd cells of this period leak and destroy the tracks around them. See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Maintenance

Main article: Acorn A5000 Maintenance Guide

The jobs in order of priority: remove and assess the backup cell; inspect and replace the surface-mount electrolytics; check the four PSU rails; replace or substitute the IDE drive, which after thirty years is usually the component that has failed; and clean the podule contacts.

Troubleshooting

Main article: Acorn A5000 Troubleshooting Guide

Acorn's functional test suite — memory, battery-backed RAM, IDE interface, hardware check, external ports, disc interface, real time, audio, video, keyboard and mouse — is in the Acorn A5000 Service Manual with the action to take on each failure. Two checks from it that catch common mistakes: the memory test will fail if links LK23 and LK24 do not match the memory fitted, and the IDE test will fail if the machine's configuration is not set to IDEdiscs 1.

Capacitor replacement

Main article: Acorn A5000 Capacitor Guide

See the Acorn A5000 Capacitor Guide; per-designator values are on Acorn A5000 Circuit Diagrams.

Replacement

The Acorn Risc PC took over as Acorn's desktop machine from 1994.

See also

• Acorn Archimedes A540 — the ARM3 flagship the A5000 undercut
• Acorn Archimedes A4000 — the ARM250 machine sold below it
• Acorn Risc PC 600 — the 1994 replacement
• Acorn A5000 Service Manual and Acorn A5000 Circuit Diagrams