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Rewrite with citations from the newly hosted Acorn Archimedes 500 / R200 Service Manual and Chris Whytehead. Corrected: SCSI is a podule that occupies a slot, not on the motherboard, so all four slots are NOT free; the SCSI controller is a WD33C93A not an NCR 53C90; the FPA11 is not an A540 part. Added BT1 NiCd 1.2 V 280 mAh with the 2.8 V on IC22 pin 8 check, the MEMC part-number warning and the FPA10 price and early-card modification. Removed the unsourced oscillator frequencies, motherboar...
Rewrite against the 500/R200 Service Manual: PSU output table, polarised capacitor list, designators, BNC socket functions, podule power; fix battery and RAM details; remove uncited claims; add board photo
 
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{{Infobox computer
{{Infobox computer
| name        = Acorn Archimedes A540
| name        = Acorn Archimedes A540
| image        = [[File:Acorn_Archimedes_A540.jpg|250px]]
| image        = [[File:Acorn_Archimedes_A540.jpg|260px|frameless]]
| caption      = Acorn Archimedes A540
| caption      = Archimedes A540 with colour monitor and keyboard
| manufacturer = Acorn Computers Ltd
| manufacturer = Acorn Computers Ltd
| type        = Personal computer (three-box desktop)
| type        = Personal computer (three-box desktop)
| release date = June 1990
| release date = June 1990
| discontinued = 1992
| price        = £2,495 ex VAT, no monitor
| price        = £2,495 ex VAT, no monitor
| cpu          = ARM3 on a replaceable CPU card, 25/26 MHz as shipped; 33 MHz cards exist
| cpu          = ARM3 on a plug-in processor card
| memory      = 4 MB RAM, expandable to 16 MB with up to three 4 MB RAM cards
| memory      = 4 MB, expandable to 16 MB with three 4 MB RAM cards
| storage      = 3.5" floppy drive (800 KB); 100 MB SCSI hard disc on an Acorn SCSI podule
| storage      = 3.5" floppy drive; 100 MB SCSI hard disc on an Acorn SCSI podule
| sound        = 8-channel, 8-bit logarithmic (VIDC1a)
| display      = Analogue RGB (VIDC1a); high-resolution mono on three BNC sockets
| sound        = 8 channels, stereo (VIDC1a)
| os          = RISC OS 2.01
| os          = RISC OS 2.01
| predecessor  = [[Acorn Archimedes A440]]
| predecessor  = [[Acorn Archimedes A440]]
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}}
}}
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The '''Acorn Archimedes A540''' was launched in June 1990 as the flagship of the Archimedes range. It was the first Acorn machine with an ARM3 as standard, the only one that could be taken to 16 MB of memory, and — with an ARM3 and an FPA10 fitted — more powerful than the later [[Acorn Archimedes A5000|A5000]].<ref name="chris540">Whytehead, Chris. [https://chrisacorns.computinghistory.org.uk/Computers/A540.html "Acorn Archimedes A540"], Chris's Acorns / The Centre for Computing History.</ref>
The '''Acorn Archimedes A540''' was launched in June 1990 as the top model of the Archimedes range, at £2,495 ex VAT without a monitor. It had an ARM3 as standard and was the only Archimedes that could be expanded to 16 MB. It came with a SCSI podule and a 100 MB hard disc.<ref name="chris540">Whytehead, Chris. [https://chrisacorns.computinghistory.org.uk/Computers/A540.html "Acorn Archimedes A540"], Chris's Acorns, archived by The Centre for Computing History. Launch, price, RAM cards, SCSI podule, PSU fans, BNC sockets, backplane and motherboard part numbers, and two documented machines with measured figures.</ref>


It costs £2,495 plus VAT without a monitor, and shares its hardware with Acorn's R260 RISC iX workstation: the A540 is an R260 without RISC iX installed, which could be bought separately and installed later.<ref name="chris540" /> Acorn documented the two together in the [[Acorn Archimedes 500 Series and R200 Series Service Manual]].<ref name="sm500">Acorn Computers Limited, ''Acorn Archimedes 500 series / Acorn R200 series Service Manual'', Issue 2, June 1991. Part 5 component-level fault diagnosis and Part 6 parts lists. Hosted on this wiki: [[Acorn Archimedes 500 Series and R200 Series Service Manual]].</ref>
The A540 has the same hardware as Acorn's R260 RISC iX workstation, without RISC iX installed.<ref name="chris540" /> Acorn documented it with the R200 series in the [[Acorn Archimedes 500 Series and R200 Series Service Manual]].<ref name="sm500">Acorn Computers Limited, ''Acorn Archimedes 500 series / Acorn R200 series Service Manual'', part number 0486,056, issue 2, June 1991. System description pp. 1-1 to 1-2; power supply p. 1-15; sockets and podule power p. 1-19; SCSI interface pp. 2-18 onwards; disassembly p. 3-2; fault diagnosis pp. 4-2 and 5-23 to 5-27; parts lists pp. 6-1 to 6-10. Hosted on this wiki: [[Acorn Archimedes 500 Series and R200 Series Service Manual]].</ref>


== Memory system ==
== Processor ==
 
The ARM3 is on a daughter card that plugs into PL3 on the main board.<ref name="sm500" /> Chris Whytehead's two A540s have an original 26 MHz card (VL86C020), which has no socket for the FPA10, and a 33 MHz card (VY86C020-35) with an FPA10 fitted. With ARMSi v4.0 they measure 14.14 and 16.8 MIPS.<ref name="chris540" />
 
=== FPA10 floating point accelerator ===


This is what makes the A540 unusual. A single MEMC1a addresses a maximum of 4 MB, so Acorn put a MEMC1a on the motherboard and gave the machine three further sockets, SK5, SK6 and SK7, for '''RAM cards that each carry their own MEMC1a and their own 4 MB'''. Configurations are therefore 4, 8, 12 or 16 MB.<ref name="chris540" /><ref name="sm500" />
Acorn released the FPA10 in July 1993 for the A540, the A5000 and the R260, at £99 ex VAT. On the A540 it fits a socket on the processor card. Acorn gave its dissipation as 250 mW and its peak throughput as up to 5 MFLOPS at 26 MHz. Owners of early A540s and R260s might need a free modification to the processor card before fitting one, and RISC iX needs an extra driver.<ref name="prfpa">Acorn Computers Limited, press release "Acorn Releases Floating Point Accelerator", 5 July 1993. [https://chrisacorns.computinghistory.org.uk/docs/Acorn/PR/FPA_release.txt Text] via Chris's Acorns.</ref>


The motherboard's DRAM is 1M × 1 80 ns in 20-pin ZIP packages; the 4 MB cards use 1M × 4 80 ns SOJ devices with a MEMC1a at IC10. Acorn's parts list carries an explicit warning: '''MEMCs must be Acorn part number 2201,393''' to guarantee correct timing.<ref name="sm500" /> The memory clock runs at '''12 MHz''', against 8 MHz on the A300, A400 and A400/1 machines.<ref name="chris540" /><ref name="sm500" /> Acorn and Simtec both made RAM cards.<ref name="chris540" />
== Memory ==


The memory cards are the machine's known weak point. Chris Whytehead reports that an A540 left unused for a while becomes temperamental and that the RAM cards in particular are liable to work loose; reseating them is the first thing to try on an unstable machine.<ref name="chris540" />
A MEMC addresses at most 4 MB, so the A540 has a MEMC1a and 4 MB on the main board and three sockets, SK5, SK6 and SK7, for RAM cards that each carry their own MEMC1a and 4 MB. A machine therefore has 4, 8, 12 or 16 MB.<ref name="chris540" /><ref name="sm500" />


== Processor ==
The main board uses thirty-two 1M × 1 80 ns DRAMs in 20-pin ZIP packages, with the master MEMC1a at IC60. Each RAM card has eight 1M × 4 80 ns SOJ DRAMs and its MEMC1a at IC10. Acorn's parts list states that the MEMCs must be Acorn part number 2201,393 to get the right timing.<ref name="sm500" /> Chris Whytehead records a 12 MHz memory clock on both his A540s, and Acorn and Simtec both made RAM cards.<ref name="chris540" /> Acorn's parts lists give every MEMC1a in the machine as a 12 MHz part.<ref name="sm500" />
 
Chris Whytehead finds the A540 temperamental after a period out of use, and the RAM cards liable to work loose.<ref name="chris540" />


The ARM3 sits on a replaceable CPU card. Machines shipped with 25 or 26 MHz parts; 33 MHz cards exist and are found on upgraded machines. Chris Whytehead's two documented A540s carry a VL86C020 at 26 MHz (the original card, with no FPA socket) and a VY86C020-35 at 33 MHz with an FPA10 fitted.<ref name="chris540" />
== Video and sound ==


Measured on those machines with ARMSi v4.0: 14.14 MIPS for the 26 MHz card and 16.8 MIPS for the 33 MHz card with FPA10.<ref name="chris540" />
The A540 uses the VIDC1a.<ref name="chris540" /> Acorn's parts list places it at IC64 and lists IC54 as a 74S00, but the fault-finding pages of the same manual refer to the VIDC as IC54.<ref name="sm500" /> The three BNC sockets on the rear panel, found only on the A540 and R260, are SK12 to SK14: high-resolution mono video (0.7 V into 75 ohms at a 96 MHz dot rate), vertical sync and horizontal sync.<ref name="chris540" /><ref name="sm500" /> Sound is eight channels, each with its own stereo position.<ref name="sm500" />


=== FPA10 floating point accelerator ===
== SCSI ==


Acorn released the FPA10 in July 1993 for the A540, the A5000 and the R260, at '''£99 ex VAT'''. It fits a socket designed for it on the A540's processor card. Acorn's figures: 250 mW dissipation, peak throughput up to 5 MFLOPS at 26 MHz and an average above 3 MFLOPS, with floating point performance under the RISC OS floating point emulator increasing by as much as a factor of 50.<ref name="prfpa">Acorn Computers Limited press release, "Acorn Releases Floating Point Accelerator", 5 July 1993. [https://chrisacorns.computinghistory.org.uk/docs/Acorn/PR/FPA_release.txt Text] via Chris's Acorns.</ref>
The A540's SCSI interface is a podule, not part of the main board, so one of the four slots is occupied from new.<ref name="chris540" /> Chris Whytehead's machines have the Acorn AKA31 (0173,010) and AKA32 Mk3 (0173,080).<ref name="chris540" /> Acorn's manual describes the card at component level: a Western Digital WD33C93A SCSI bus controller, an NEC μPD71071 DMA controller and 32K × 16 of static RAM.<ref name="sm500" />


Acorn's own release note adds a repair-relevant point: '''owners of early A540s and R260s may need a free-of-charge modification to their processor cards''' before an FPA10 will work, and RISC iX users need an additional software driver.<ref name="prfpa" />
== Power supply and expansion ==


The FPA10 is the only floating point accelerator for this machine. The FPA11 is a different part and is not an A540 upgrade.
The power supply is larger than a standard Archimedes unit and has two fans.<ref name="chris540" /> Acorn's specification for it:<ref name="sm500" />


== SCSI ==
{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''A540 power supply outputs (Acorn specification)'''
! Rail !! Minimum !! Nominal !! Maximum !! Current !! Ripple and noise
|-
| +5 V || 4.9 V || 5 V || 5.1 V || 1.5–12.2 A || 50 mV pk-pk
|-
| +12 V || 11.4 V || 12 V || 12.6 V || 0–3.2 A || 100 mV pk-pk
|-
| −5 V || −4.5 V || −5 V || −5.5 V || 0–0.3 A || 50 mV pk-pk
|}


The A540's SCSI is '''not''' on the motherboard. Unlike the rest of the range it shipped with a SCSI podule as standard, together with a 100 MB SCSI hard disc — so one of the four podule slots is occupied from new.<ref name="chris540" /> Documented machines carry the Acorn AKA31 (part 0173,010) or the AKA32 Mk3 (part 0173,080).<ref name="chris540" />
Total output is 100 W continuous and 122 W surge. The +5 V over-voltage protection trips between 5.8 V and 7.0 V. The input is 198–264 V AC at 47–53 Hz, with a 98–132 V version as a manufacturing option.<ref name="sm500" />


Acorn's service manual documents the SCSI expansion card down to component level. It is built around a '''Western Digital WD33C93A''' SCSI bus interface controller and an NEC 71071 DMA controller, with two 32K × 8 static RAMs, a driver EPROM and five PALs.<ref name="sm500" />
The backplane is Acorn part 0186,001 with four slots, and the main board is 0186,000.<ref name="chris540" /> Each podule slot may draw up to 1 A at +5 V, 250 mA at +12 V and 50 mA at −5 V.<ref name="sm500" /> Cards on Chris Whytehead's machines include an Atomwide Ethernet IV, a Computer Concepts Colour Card, a Computer Concepts ScanLight interface and an Aleph One 386 PC card.<ref name="chris540" />


== Video ==
[[File:Acorn Archimedes A540 motherboard.jpg|thumb|360px|A540 with the backplane, processor card and RAM cards removed. The rear panel with its three BNC sockets is at the bottom.]]


The A540 uses the VIDC1a, as the rest of the Archimedes range does.<ref name="chris540" /> It and the R260 carry '''three BNC connectors''' on the rear panel that appear on no other Acorn machine.<ref name="chris540" />
== Capacitors ==


== Expansion and construction ==
Acorn's main board parts list mixes radial electrolytics, tantalums, ceramics and surface-mount decouplers in one C-number sequence. The polarised parts are:<ref name="sm500" />


The backplane is Acorn part 0186,001, four slots; the motherboard is part 0186,000 Issue 1.<ref name="chris540" /> The power supply is physically larger than a standard Archimedes unit and contains '''two fans'''.<ref name="chris540" />
{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''A540 polarised capacitors (Acorn parts lists, pp. 6-1, 6-2, 6-6 and 6-7)'''
! Board !! Designators !! Value and type
|-
| Main board || C1–C4, C186–C195 || 10 µF 10 V tantalum
|-
| Main board || C5, C6, C13, C19, C20, C21, C24, C27, C30, C35, C37 || 220 µF 16 V radial electrolytic
|-
| Main board || C7, C9, C16, C23, C26, C29, C33 || 47 µF 16 V radial electrolytic
|-
| Main board || C8, C14 || 4.7 µF 16 V radial electrolytic
|-
| Main board || C10, C15 || 1000 µF 25 V radial electrolytic
|-
| Main board || C11, C12, C18, C31, C34, C36 || 10 µF 16 V radial electrolytic
|-
| Main board || C17 || 100 µF 25 V radial electrolytic
|-
| 4 MB RAM card || C1–C4 || 47 µF surface-mount tantalum
|-
| Backplane || C4, C5, C6 || 47 µF 16 V axial electrolytic
|-
| ARM3 card || C1, C2 || 47 µF 10 V axial electrolytic
|}


Cards documented on surviving A540s include the Atomwide Ethernet IV, the Wild Vision / Computer Concepts Colour Card and Colour Card Gold, the Computer Concepts ScanLight scanner interface, and the Aleph One 386 PC card.<ref name="chris540" />
C22, C25, C28 and C32, in the middle of the electrolytic run, are 47 nF ceramics. Acorn's video fault procedure checks for +5 V at both ends of L1 and, if it is open, for C9 short-circuit.<ref name="sm500" />


== Backup battery ==
== Backup battery ==


The A540's backup battery is '''BT1, a NiCd 1.2 V 280 mAh cell mounted on the PCB''', with a foam pad beneath it. It is a soldered rechargeable cell, not a holder of AA cells as in the A300, A400 and A400/1 machines, and not a 3.6 V pack.<ref name="sm500" />
The clock and CMOS RAM are backed by BT1, a 1.2 V 280 mAh NiCd cell soldered to the main board, with a foam pad beneath it.<ref name="sm500" /> It is a rechargeable cell, unlike the two AA alkaline cells of the A440 and the earlier machines.<ref name="sm440">Acorn Computers Limited, ''High Performance Computer Systems Model 440 Service Manual'', part number 0476,155, issue 1, November 1988, p. 6 (internal batteries). Hosted on this wiki: [[Archimedes 440 Service Manual]].</ref>


Acorn's component-level check, from the service manual: if the non-volatile memory loses data and the real-time clock fails, then '''with the machine switched off, look for about 2.8 V on IC22 pin 8'''. If that voltage is absent, check the charge state of BT1. If the NVM at IC22 consistently fails on the same data bits, change the device. If the clock runs inaccurately or not at all, check and if necessary replace crystal X3; LK8 gives access to the clock signal.<ref name="sm500" />
Acorn's check: if the configuration memory loses its contents and the clock fails, measure IC22 pin 8 with the power off. It should be about 2.8 V; if not, check the charge state of BT1. If the PCF8583 at IC22 always fails on the same data bits, change it. If the clock stops or runs inaccurately, check crystal X3; LK8 gives access to the clock signal.<ref name="sm500" />


Thirty-year-old NiCd cells on Acorn boards leak and corrode the tracks around them. Remove BT1 before powering a stored machine — see [[Battery Explosion, Capacitor or Corrosion Damage]] and [[Battery Refurbishment]].
Old NiCd cells leak electrolyte that corrodes the tracks around them. Remove BT1 from a stored machine before powering it; see [[Battery Explosion, Capacitor or Corrosion Damage]] and [[Battery Refurbishment]].


== Operating system ==
== Operating system ==


The A540 launched with RISC OS 2.01, dated 5 July 1990 in the ROM.<ref name="chris540" /> Many machines were later taken to RISC OS 3.10 or 3.11 by ROM swap; Chris Whytehead's first A540 runs 3.11 with the Acorn Universal Boot installed.<ref name="chris540" /> His second, bought from an ex-Acorn employee, still runs RISC OS 2.01 with SJ Research Nexus Level 4 fileserver software for Econet — a reminder that an unmodified A540 is worth leaving unmodified.<ref name="chris540" />
The A540 shipped with RISC OS 2.01 (ROMs dated 5 July 1990). Chris Whytehead's first machine has been upgraded to RISC OS 3.11 with the Acorn Universal Boot; his second, from an ex-Acorn employee, still runs RISC OS 2.01 with SJ Research Nexus Level 4 Econet fileserver software.<ref name="chris540" /> The four RISC OS ROMs are IC47 to IC50.<ref name="sm500" />


== Serial port ==
== Serial port ==


The A500/R200 serial port is based on the '''RS232''' standard, unlike the RS423-based port on the earlier Archimedes machines, and the RS423 Drive software patch (version 1.24) needed on those machines is not required here.<ref name="sm500" />
The 500 and R200 series serial port follows RS232, unlike the RS423 port of the earlier Archimedes machines, and the RS423 Drive patch (version 1.24) used on those is not needed.<ref name="sm500" />


== Maintenance and repair ==
== Maintenance and repair ==


* '''Remove BT1''' and inspect the board around it before applying power to a stored machine.
* Remove BT1 and inspect the board around it before powering a stored machine.
* '''Reseat the RAM cards''' in SK5–SK7 on any machine that is unstable or reports the wrong memory size.
* Measure +5 V, +12 V and −5 V against the table above before chasing other faults.
* '''Check the FPA card modification''' if an FPA10 does not work in an early machine.<ref name="prfpa" />
* Reseat the RAM cards in SK5 to SK7 on a machine that is unstable or reports the wrong memory size.
* '''Two fans''' — check both turn. The A540 runs hot and the memory cards are heat-sensitive.
* For a dead machine, Acorn's procedure swaps the processor card, MEMC IC60, IOC IC58 and the VIDC in turn, then checks the 24 MHz system clock at LK11 and the 96 MHz oscillator at IC57.<ref name="sm500" />
* '''SCSI drive''' — see [[Hard Drive Maintenance and Repair]].
* Check that both power supply fans turn.
* '''Floppy drive''' — documented machines use the Citizen OSDC-65C. See [[Floppy Drive Repair]].
* If an FPA10 does not work in an early machine, the processor card may need Acorn's modification.<ref name="prfpa" />
* '''Tools''' — see [[Recommended Tools]].
* Acorn's SCSI drive test reformats the disc and destroys its data.<ref name="sm500" /> See [[Hard Drive Maintenance and Repair]] and, for the Citizen OSDC-65C floppy drive on Chris Whytehead's machines,<ref name="chris540" /> [[Floppy Drive Repair]].
 
Acorn's manual treats the power supply as a replaceable module with no user-serviceable parts and gives no component list for it.<ref name="sm500" />
 
== Documentation ==


Component-level fault diagnosis, the functional test suite and full parts lists for the main PCB, RAM card, backplane, ARM3 card, keyboard, Ethernet and SCSI cards — including every capacitor designator and value — are in the [[Acorn Archimedes 500 Series and R200 Series Service Manual]] hosted here.<ref name="sm500" />
* [[Acorn Archimedes 500 Series and R200 Series Service Manual]]: part 0486,056, issue 2, June 1991. System description, interface cards, disassembly, functional tests, component-level fault finding and parts lists for the main board, RAM card, backplane, ARM3 card, keyboard, Ethernet and SCSI cards.


== See also ==
== See also ==


* [[Acorn Archimedes A440]] — the flagship it replaced
* [[Acorn Archimedes A440]], the 1987 top model it replaced
* [[Acorn Archimedes A5000]] — the 1991 ARM3 machine that undercut it
* [[Acorn Archimedes A410]] and [[Acorn Archimedes A420]], the 400/1 range
* [[Acorn Archimedes A410]] and [[Acorn Archimedes A420]] — the A400/1 range
* [[Acorn Archimedes A5000]], the 1991 ARM3 machine
* [[Acorn Archimedes 500 Series and R200 Series Service Manual]]


== References ==
== References ==

Latest revision as of 07:45, 1 October 2026

Acorn Archimedes A540
Archimedes A540 with colour monitor and keyboard
Specifications
ManufacturerAcorn Computers Ltd
TypePersonal computer (three-box desktop)
ReleasedJune 1990
Intro price£2,495 ex VAT, no monitor
CPUARM3 on a plug-in processor card
Memory4 MB, expandable to 16 MB with three 4 MB RAM cards
Storage3.5" floppy drive; 100 MB SCSI hard disc on an Acorn SCSI podule
DisplayAnalogue RGB (VIDC1a); high-resolution mono on three BNC sockets
Sound8 channels, stereo (VIDC1a)
OS / FirmwareRISC OS 2.01
PredecessorAcorn Archimedes A440
SuccessorAcorn Archimedes A5000
Model no.AKB50

The Acorn Archimedes A540 was launched in June 1990 as the top model of the Archimedes range, at £2,495 ex VAT without a monitor. It had an ARM3 as standard and was the only Archimedes that could be expanded to 16 MB. It came with a SCSI podule and a 100 MB hard disc.[1]

The A540 has the same hardware as Acorn's R260 RISC iX workstation, without RISC iX installed.[1] Acorn documented it with the R200 series in the Acorn Archimedes 500 Series and R200 Series Service Manual.[2]

Processor

[edit | edit source]

The ARM3 is on a daughter card that plugs into PL3 on the main board.[2] Chris Whytehead's two A540s have an original 26 MHz card (VL86C020), which has no socket for the FPA10, and a 33 MHz card (VY86C020-35) with an FPA10 fitted. With ARMSi v4.0 they measure 14.14 and 16.8 MIPS.[1]

FPA10 floating point accelerator

[edit | edit source]

Acorn released the FPA10 in July 1993 for the A540, the A5000 and the R260, at £99 ex VAT. On the A540 it fits a socket on the processor card. Acorn gave its dissipation as 250 mW and its peak throughput as up to 5 MFLOPS at 26 MHz. Owners of early A540s and R260s might need a free modification to the processor card before fitting one, and RISC iX needs an extra driver.[3]

Memory

[edit | edit source]

A MEMC addresses at most 4 MB, so the A540 has a MEMC1a and 4 MB on the main board and three sockets, SK5, SK6 and SK7, for RAM cards that each carry their own MEMC1a and 4 MB. A machine therefore has 4, 8, 12 or 16 MB.[1][2]

The main board uses thirty-two 1M × 1 80 ns DRAMs in 20-pin ZIP packages, with the master MEMC1a at IC60. Each RAM card has eight 1M × 4 80 ns SOJ DRAMs and its MEMC1a at IC10. Acorn's parts list states that the MEMCs must be Acorn part number 2201,393 to get the right timing.[2] Chris Whytehead records a 12 MHz memory clock on both his A540s, and Acorn and Simtec both made RAM cards.[1] Acorn's parts lists give every MEMC1a in the machine as a 12 MHz part.[2]

Chris Whytehead finds the A540 temperamental after a period out of use, and the RAM cards liable to work loose.[1]

Video and sound

[edit | edit source]

The A540 uses the VIDC1a.[1] Acorn's parts list places it at IC64 and lists IC54 as a 74S00, but the fault-finding pages of the same manual refer to the VIDC as IC54.[2] The three BNC sockets on the rear panel, found only on the A540 and R260, are SK12 to SK14: high-resolution mono video (0.7 V into 75 ohms at a 96 MHz dot rate), vertical sync and horizontal sync.[1][2] Sound is eight channels, each with its own stereo position.[2]

SCSI

[edit | edit source]

The A540's SCSI interface is a podule, not part of the main board, so one of the four slots is occupied from new.[1] Chris Whytehead's machines have the Acorn AKA31 (0173,010) and AKA32 Mk3 (0173,080).[1] Acorn's manual describes the card at component level: a Western Digital WD33C93A SCSI bus controller, an NEC μPD71071 DMA controller and 32K × 16 of static RAM.[2]

Power supply and expansion

[edit | edit source]

The power supply is larger than a standard Archimedes unit and has two fans.[1] Acorn's specification for it:[2]

A540 power supply outputs (Acorn specification)
Rail Minimum Nominal Maximum Current Ripple and noise
+5 V 4.9 V 5 V 5.1 V 1.5–12.2 A 50 mV pk-pk
+12 V 11.4 V 12 V 12.6 V 0–3.2 A 100 mV pk-pk
−5 V −4.5 V −5 V −5.5 V 0–0.3 A 50 mV pk-pk

Total output is 100 W continuous and 122 W surge. The +5 V over-voltage protection trips between 5.8 V and 7.0 V. The input is 198–264 V AC at 47–53 Hz, with a 98–132 V version as a manufacturing option.[2]

The backplane is Acorn part 0186,001 with four slots, and the main board is 0186,000.[1] Each podule slot may draw up to 1 A at +5 V, 250 mA at +12 V and 50 mA at −5 V.[2] Cards on Chris Whytehead's machines include an Atomwide Ethernet IV, a Computer Concepts Colour Card, a Computer Concepts ScanLight interface and an Aleph One 386 PC card.[1]

A540 with the backplane, processor card and RAM cards removed. The rear panel with its three BNC sockets is at the bottom.

Capacitors

[edit | edit source]

Acorn's main board parts list mixes radial electrolytics, tantalums, ceramics and surface-mount decouplers in one C-number sequence. The polarised parts are:[2]

A540 polarised capacitors (Acorn parts lists, pp. 6-1, 6-2, 6-6 and 6-7)
Board Designators Value and type
Main board C1–C4, C186–C195 10 µF 10 V tantalum
Main board C5, C6, C13, C19, C20, C21, C24, C27, C30, C35, C37 220 µF 16 V radial electrolytic
Main board C7, C9, C16, C23, C26, C29, C33 47 µF 16 V radial electrolytic
Main board C8, C14 4.7 µF 16 V radial electrolytic
Main board C10, C15 1000 µF 25 V radial electrolytic
Main board C11, C12, C18, C31, C34, C36 10 µF 16 V radial electrolytic
Main board C17 100 µF 25 V radial electrolytic
4 MB RAM card C1–C4 47 µF surface-mount tantalum
Backplane C4, C5, C6 47 µF 16 V axial electrolytic
ARM3 card C1, C2 47 µF 10 V axial electrolytic

C22, C25, C28 and C32, in the middle of the electrolytic run, are 47 nF ceramics. Acorn's video fault procedure checks for +5 V at both ends of L1 and, if it is open, for C9 short-circuit.[2]

Backup battery

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The clock and CMOS RAM are backed by BT1, a 1.2 V 280 mAh NiCd cell soldered to the main board, with a foam pad beneath it.[2] It is a rechargeable cell, unlike the two AA alkaline cells of the A440 and the earlier machines.[4]

Acorn's check: if the configuration memory loses its contents and the clock fails, measure IC22 pin 8 with the power off. It should be about 2.8 V; if not, check the charge state of BT1. If the PCF8583 at IC22 always fails on the same data bits, change it. If the clock stops or runs inaccurately, check crystal X3; LK8 gives access to the clock signal.[2]

Old NiCd cells leak electrolyte that corrodes the tracks around them. Remove BT1 from a stored machine before powering it; see Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Operating system

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The A540 shipped with RISC OS 2.01 (ROMs dated 5 July 1990). Chris Whytehead's first machine has been upgraded to RISC OS 3.11 with the Acorn Universal Boot; his second, from an ex-Acorn employee, still runs RISC OS 2.01 with SJ Research Nexus Level 4 Econet fileserver software.[1] The four RISC OS ROMs are IC47 to IC50.[2]

Serial port

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The 500 and R200 series serial port follows RS232, unlike the RS423 port of the earlier Archimedes machines, and the RS423 Drive patch (version 1.24) used on those is not needed.[2]

Maintenance and repair

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  • Remove BT1 and inspect the board around it before powering a stored machine.
  • Measure +5 V, +12 V and −5 V against the table above before chasing other faults.
  • Reseat the RAM cards in SK5 to SK7 on a machine that is unstable or reports the wrong memory size.
  • For a dead machine, Acorn's procedure swaps the processor card, MEMC IC60, IOC IC58 and the VIDC in turn, then checks the 24 MHz system clock at LK11 and the 96 MHz oscillator at IC57.[2]
  • Check that both power supply fans turn.
  • If an FPA10 does not work in an early machine, the processor card may need Acorn's modification.[3]
  • Acorn's SCSI drive test reformats the disc and destroys its data.[2] See Hard Drive Maintenance and Repair and, for the Citizen OSDC-65C floppy drive on Chris Whytehead's machines,[1] Floppy Drive Repair.

Acorn's manual treats the power supply as a replaceable module with no user-serviceable parts and gives no component list for it.[2]

Documentation

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  • Acorn Archimedes 500 Series and R200 Series Service Manual: part 0486,056, issue 2, June 1991. System description, interface cards, disassembly, functional tests, component-level fault finding and parts lists for the main board, RAM card, backplane, ARM3 card, keyboard, Ethernet and SCSI cards.

See also

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References

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  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 Whytehead, Chris. "Acorn Archimedes A540", Chris's Acorns, archived by The Centre for Computing History. Launch, price, RAM cards, SCSI podule, PSU fans, BNC sockets, backplane and motherboard part numbers, and two documented machines with measured figures.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20 Acorn Computers Limited, Acorn Archimedes 500 series / Acorn R200 series Service Manual, part number 0486,056, issue 2, June 1991. System description pp. 1-1 to 1-2; power supply p. 1-15; sockets and podule power p. 1-19; SCSI interface pp. 2-18 onwards; disassembly p. 3-2; fault diagnosis pp. 4-2 and 5-23 to 5-27; parts lists pp. 6-1 to 6-10. Hosted on this wiki: Acorn Archimedes 500 Series and R200 Series Service Manual.
  3. ↑ 3.0 3.1 Acorn Computers Limited, press release "Acorn Releases Floating Point Accelerator", 5 July 1993. Text via Chris's Acorns.
  4. ↑ Acorn Computers Limited, High Performance Computer Systems Model 440 Service Manual, part number 0476,155, issue 1, November 1988, p. 6 (internal batteries). Hosted on this wiki: Archimedes 440 Service Manual.


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