Acorn Archimedes A3010 Troubleshooting Guide

A3010 main PCB circuit diagram, sheet 2 of 3 (drawing 0194,000): mains input and DC rails at the top left, the audio hybrid at the top right. Sheets 1 and 3 are also hosted.

Fault finding on the Acorn Archimedes A3010 follows Acorn's Module Level Service Manual, which has flowcharts for a dead computer and a dead supply, the power-on self-test codes, and an action for each test on Acorn's dealer test disc. Acorn's dealers replaced whole modules; the Technical Reference Manual adds the supply description, links and parts lists needed to go further.

Before you start

Warning: the supply is part of the main board. Acorn warns of hazardous voltages on the board once the metal safety case is removed, and on the underside of the board if it is connected to the mains outside its metalwork. Disconnect the computer, monitor and peripherals before opening it.

• Save the CMOS settings first if the machine still runs. Acorn's procedure saves them to a data disc, and some fixes below reset them to factory defaults.
• After any repair, Acorn requires earth continuity and DC insulation tests (Appendices C and D).

Dead computer

Acorn's Figure 1-1 for a computer that appears dead:

1. Connect the customer's monitor, mouse and monitor cable to a known working computer. If that fails to start, substitute a working monitor, cable and mouse 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 it still fails, remove all memory upgrades, set the RAM size links for the base memory and do another delete power-on. If that cures it, the upgrade is at fault; if not, the main board is.
5. If the display is purple or red, the self-test has stopped on a fault (see below).

Supply

A3010 supply faults (Service Manual pp. 1-3 and 1-6; TRM p. 1-18)

Symptom	Probable cause	Action
No power LED, no Caps Lock LED response	Mains lead, plug fuse, FS1, transformer	Check the plug fuse (3 A) and FS1 (250 mA T). Unplug the mains lead from PL1 and check the lead: earth-live, earth-neutral and live-neutral all open circuit. Then check PL1 on the board: earth-live and earth-neutral open circuit, live-neutral about 5 Ω (Acorn's text says 4 Ω).
PL1 live-neutral open circuit	Transformer thermal fuse	The thermal fuse inside the transformer has probably blown. Acorn says not to bypass it; replace the transformer after finding the cause.
Plug fuse and FS1 both blown, or FS1 alone	Fault on the board	Acorn's dealers returned the board. Look for a short on the supply side.
A function fails on one rail	Link out, loose drive cable	Check LK1 (5 V) and LK2 (12 V) are fitted and the drive cables are firmly attached.
Runs, then cuts out	Thermal shutdown	Test the transformer's thermal fuse at PL1 as above.
Starts only after several attempts with upgrades fitted	Supply at its limit	Remove upgrades and retest. Acorn notes a wide spread in the current limit of the L4960 between units.

A3010 supply test points (TRM p. 1-18, 240 V input)

Point	Nominal
TP1	About 23 V, input to the L4960 (Q2)
LK1	5 V logic rail
LK2	Regulated 12 V from the 78L12 (Q1); remove LK2 to isolate it
TP2	+12 V unregulated, 50 mA
TP3	-12 V unregulated, 50 mA

Acorn's TRM gives these nominal values and no tolerances.

Power-on self-test

After a power-on reset (not after the Reset key), the machine runs a self-test lasting 2 to 12 seconds depending on memory:

1. The screen turns purple while the ROM, RAM, IOC and VIDC are checked. A machine that stops here has a major fault, probably in the I/O system.
2. Blue: a fuller memory test, up to 12 seconds on a 16 MB machine.
3. A brief VIDC test, then purple again while the test checks for an ARM3.
4. Black, with a memory size message. RISC OS then starts.

The self-test sets a 15 kHz mode, so a VGA or multisync monitor shows an unsynchronised picture until it finishes; that alone is not a fault. If a fault is found, the screen turns red and the floppy drive LED flashes an 8-digit hexadecimal code as eight groups of four flashes, long for 1 and short for 0.

Self-test fault bits (Service Manual p. 1-4)

Bit	Meaning
00000200	ROM failed checksum test
00000400	MEMC CAM mapping failed
00000800	MEMC protection failed
00001000	IOC register test failed
00004000	VIDC (Virq interrupt) timing failed
00008000	Sound (Sirq interrupt) timing failed
00010000	CMOS RAM (clock/calendar chip) unreadable
00020000	RAM control line failure
00040000	Long RAM test failure

The low bits are status, not faults: for example 00000001 power-on self-test, 00000008 long memory test performed, 00000010 ARM3 fitted, 00000100 CMOS RAM checksum error. Acorn's worked example, 00000219 on an ARM3 machine, is a ROM checksum failure.

Before returning a board, Acorn's checks are: ROMs in the right sockets with no lifted pins, ROM links correct, other socketed parts correctly placed and oriented, DRAM size links correct, and no loose debris on the board. On the A3010 the DRAM size links are LK20, LK21 and LK22 (1 MB: 1-2, not fitted, 1-2; 2 MB: 1-2, not fitted, 2-3; 4 MB: 2-3, 1-2, not fitted).

Faults on a running machine

A3010 faults on a running machine

Symptom	Probable cause	Action
No display	Monitor, monitor configuration, video links	Acorn's actions: check the monitor is powered and its brightness and contrast are up. Hold the "." key on the numeric keypad while switching on and for at least 10 seconds more, which resets the monitor configuration to suit the monitor connected. Substitute a known good monitor and cable. Inside, check the shunts on LK6 pins 3-4 and 5-6 have not been dislodged.
Corrupted display	Adaptor cable, monitor configuration	Check any adaptor cable against the Welcome Guide's monitor connections appendix and reset the monitor configuration with the "." power-on.
No floppy drive icon	Configuration, cables	Check the CMOS setting is "floppies 1". Check the 34-way data cable at the drive and at PL10, and the 4-way power cable at the drive and at PL5. The power cable should have 0 V on pins 2 and 3 and +5 V on pin 1 (the white-marked conductor).
Floppy icon present but errors on access	Cable, links, disc, drive	Substitute the data and power cables. Check links LK18, LK19 and LK21. Format a new disc and test it on another machine, then substitute the drive.
Keyboard fails	Link, keyboard	Check LK14 is made from pin 1 to pin 2, then substitute a known working keyboard.
Speaker silent, headphones work	Speaker wiring	Check the speaker cable at the board, the solder joints on the speaker tags and the two crimps in the connector shell.
Headphones silent, speaker works	Headphones	Substitute a known working pair.
Crackling sound	Audio hybrid pins, headphone socket	Stardot members traced crackle to broken pins on the audio hybrid module (IM2), and to dirty switched contacts in the headphone socket, which carry the speaker signal. One fitted a turned-pin header in place of the hybrid's original pins.
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 the BAUD and DATA settings and that the correct loopback plug is fitted.
Battery-backed RAM test fails	Test data file, board	Check the CMOS test data file is the right one; Acorn notes that later test results cannot be trusted if this test fails.
Intermittent start, Supervisor prompt with data transfer errors, RAM upgrade fitted	Upgrade contact	On Adam Wilson's machine a pin on a 3 MB RAM upgrade had been bent over. With the upgrade removed and the links set for 1 MB it started reliably; the repaired upgrade then worked.

Battery and clock

• Settings and the time lost after switch-off: BT2, the 1.2 V nickel cell, is flat, leaking or removed. It is charged from +5 V through D15, R60 and R73 and feeds the PCF8583 (IC5) through R61. Self-test fault bit 00010000 means the clock and CMOS chip could not be read.
• Corrosion from the cell: on Adam Wilson's machine it reached the top-right corner of the board, the inside of the lower shield and the parallel port. Removal and cleaning are on the Acorn Archimedes A3010 Maintenance Guide.
• Starts at the Supervisor prompt instead of the desktop: type *Desktop to start the desktop. If it happens on every cold start, the CMOS settings are not being kept; fix the battery, then do a delete power-on to restore Acorn's defaults.

Related pages

• Acorn Archimedes A3010
• Acorn Archimedes A3010 Maintenance Guide
• Acorn Archimedes A3010 Capacitor Guide
• Acorn Archimedes A3020 Troubleshooting Guide
• Acorn A3010, A3020 and A4000 Service Manual and Acorn A3010, A3020 and A4000 Technical Reference Manual