Acorn A5000 Troubleshooting Guide

A5000 main PCB circuit diagram, sheet 2 of 4: IOC, the 82C710, disc, serial and printer interfaces, keyboard, and the battery-backed RAM and clock. All sheets are at Acorn A5000 Circuit Diagrams.

Fault finding on the Acorn Archimedes A5000 follows Acorn's Module Level Service Manual: a flowchart for a dead computer, checks for the supply, the main board and upgrades, and an action for each test on Acorn's A5000 test disc (part 0292,824). Acorn's dealers replaced modules, and boards needing component-level repair went to a central workshop because the main board is surface-mount. The Acorn A5000 Circuit Diagrams supply the component detail.

Before you start

Warning: the supply runs from the mains. Disconnect the computer, monitor and peripherals before opening it, and shut it down first (F12, then SHUTDOWN) so the hard disc is parked.

• Save the CMOS settings if the machine still runs; some fixes reset them to factory defaults.
• After any repair, Acorn requires an earth continuity test at 25 A to the base metalwork, rear panels and top cover, and a DC insulation test.

Dead computer

Acorn's Figure 1-1:

1. Connect the customer's mains cable, monitor, monitor cable, mouse and keyboard to a known working computer. If that fails, substitute working ones, one at a time, to find the faulty unit.
2. Connect working peripherals to the faulty computer and switch on.
3. If the power LED does not light, go to the supply checks below.
4. If nothing is displayed, do a delete power-on (hold Delete while switching on) to restore the default CMOS settings. If that fails, remove all upgrades, noting their positions, set the RAM size links for the base memory and do another delete power-on. If it now works, refit the upgrades one at a time to find the faulty one; if not, the main board is at fault.
5. If the screen is purple or red, the start-up test has stopped on a fault; go to the main board checks below.

Supply

A5000 supply faults (Service Manual p. 1-3)

Symptom	Probable cause	Action
No fan noise, no green LED, no Caps Lock response	Plug fuse, supply	Check the mains plug fuse (5 A on UK machines). If a new fuse blows at switch-on, the supply is faulty.
Main board, floppy or hard disc dead	+5 V (PL6, PL7)	Check the fastons are secure on the board and the drive power connectors are firmly attached.
Expansion cards that need -5 V fail	-5 V (PL2)	-5 V feeds backplane pin A31. Check the faston.
No SCART picture, cards needing +12 V fail	+12 V (PL3)	+12 V feeds video connector SK1 pin 12 and backplane pins B31 and B32. Check the faston.
Runs, then shuts down	Thermal shutdown	A failed fan or a failed part in the supply. Listen for the fan and clear the fan aperture.

The fastons are PL2 -5 V (purple), PL3 +12 V (yellow), PL4 and PL5 0 V (black), PL6 and PL7 +5 V (red). Acorn's manual gives no rail tolerances.

Main board checks

Before returning a board, Acorn's checks are: ROMs in the right sockets with no lifted pins; ROM size and type links LK10, LK11, LK12 and LK14 set correctly; other socketed parts in the right place and orientation; DRAM size links LK23 and LK24 correct; and no loose debris on the board.

On a machine that has been stored, also look for damage from the backup cell, BT1, and from leaking surface-mount electrolytics. On the Stardot forum, one owner whose A5000 would only start to the Supervisor prompt, and would not respond to a CMOS reset, found pins 5-8 of the clock chip lifted from the board by battery corrosion, cracked tantalum capacitors and leaking 47 µF surface-mount electrolytics; danielj noted that the IDE and floppy interfaces near the battery may also be damaged. The battery circuit is on circuit diagram sheet 2: BT1 is charged from +5 V through D15 and R272 and feeds the PCF8583 (IC58) through R281.

Upgrades and expansion

A5000 upgrade faults (Service Manual p. 1-3)

Symptom	Probable cause	Action
Memory faults with a RAM card	Card seating, links, illegal combination	Check the card is seated in its main board socket, the ZIP chips are in their sockets, and LK23 and LK24 are set. Illegal combinations: 2 MB on the board with a 1 MB or 3 MB card; 1 MB on the board with a 2 MB card; any card with 4 MB on the board. Then substitute a known good card.
Faults on more than one expansion card	Backplane	Remove the backplane and check the pins in its plug housing and the card sockets for damage or blockage. Refit it securely in the main board socket and retest with a known working card.

With no upgrade card, LK23 and LK24 are both unconnected for 1 MB, LK24 at 2-3 for 2 MB and LK24 at 1-2 for 4 MB.

Faults on a running machine

A5000 test failures and Acorn's actions (Service Manual pp. 1-9 to 1-16)

Symptom	Probable cause	Action
No display	Monitor, monitor configuration	Check the monitor has power and its brightness and contrast are up, and that any adaptor cable is one listed in Appendix E. Hold "." on the numeric keypad while switching on and for at least 10 seconds more to reset the monitor configuration to the monitor connected.
No floppy drive icon	Configuration, cables, power	Check the CMOS setting is "floppies 1", the 34-way cable at the drive and PL10, and the 4-way power cable. The power cable should have 0 V on pins 2 and 3 and +5 V on pin 1 (white-marked conductor).
Hard disc test fails	Configuration, cable, power	Check "IDEdiscs 1", the 40-way cable at the drive and PL9, and the 4-way power connector: 0 V on pins 2 and 3 (black), +5 V on pin 4 (red), +12 V on pin 1 (yellow). Substitute the data cable.
Speaker silent, headphones work	Speaker wiring, configuration	Check the speaker cable, the solder joints on the speaker tags and the two crimps in the shell, and that the CMOS configuration has not muted the speaker or turned the volume down.
Headphones silent	Headphones	Substitute a known working pair.
Mouse fails	Mouse type, configuration, ball	Check the mouse type matches the test data, and MouseStep. Substitute a known working mouse of the same type, which shows whether the fault is in the mouse or the keyboard's mouse interface. Clean a sticking ball.
Keyboard fails	Keyboard or main board links	Substitute a known working keyboard. If the original is faulty, open it and inspect its PCB. If a working keyboard also fails, check the keyboard link shunts on the main board (LK1, LK2, LK4 and LK5 at 1-2, among others listed on p. 1-15).
Printer test fails	Configuration, printer	Check the PRINTER and IGNORE settings, the printer type, that the printer is on line, and the lead.
Serial test fails	Configuration, loopback plug	Check BAUD and DATA and that the correct loopback plug is fitted.
Battery-backed RAM test fails	Test data file, board	Check the CMOS test data file; Acorn notes that later results cannot be trusted if this test fails.
Real-time clock test fails	Board	Refer to the main board checks.

Other known faults

• Disc corruption on early machines. The first A5000 models (ALB10, ALB12, ALB14) shipped with RISC OS 3.00, which has a bug in the ADFSBuffers code that corrupts discs; set ADFSBuffers to 0, or fit RISC OS 3.10 or 3.11 ROMs.
• Leaking surface-mount electrolytics. See the Acorn A5000 Capacitor Guide.

Related pages

• Acorn Archimedes A5000
• Acorn A5000 Maintenance Guide
• Acorn A5000 Capacitor Guide
• Acorn A5000 Service Manual and Acorn A5000 Circuit Diagrams
• Acorn Archimedes A3010 Troubleshooting Guide