Acorn Archimedes A3010 Maintenance Guide

A3010 main board with the ARM250. The supply is at the top left; the backup cell BT2 is at the top right, under the floppy drive.

The Acorn Archimedes A3010 is Acorn's 1992 ARM250 home computer, with the keyboard, main board, power supply and floppy drive in one case. Its clock and settings are kept by BT2, a rechargeable nickel cell soldered to the board, and leakage from it is the main threat to a stored machine. Acorn's Service Manual and Technical Reference Manual cover disassembly, fault finding and the parts lists.

Safety

Warning: the power supply is built onto the main board. Mains voltage reaches the board through the inlet PL1, the switch and fuse FS1 to the transformer. 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. Unplug the computer, monitor and peripherals before opening it.

After any work inside, Acorn requires full functional and safety tests: earth continuity (Appendix C) and DC insulation (Appendix D).

Identify your board

Acorn's parts lists cover two kinds of A3010 board. Early boards carry a daughter card with a discrete-component version of the ARM250; later boards have the ARM250 chip itself (IC13). The two are functionally the same and most parts share positions and references, but the battery was moved. Chris Whytehead records boards numbered 0194,004 (daughter card), 0194,003 and 0195,200 (ARM250).

A3010 ARM250 main board, principal parts (TRM pp. 2-13 to 2-16)

Designator	Part
IC13	ARM250 (0294,030)
IC17, IC18	RISC OS ROMs 1 and 2 (socketed)
IC21, IC22	256K × 16 DRAM
IC24	82C711 peripheral controller
IC2	Keyboard controller
IC5	8583 clock and CMOS RAM
IC10	LM386 speaker amplifier
IM2	Audio hybrid module (0194,007)
BT2	Nickel 1.2 V 280 mAh cell (0817,014)
L1	Mains transformer, 25 VA 240 V
Q2	L4960 switching regulator (5 V)
Q1	78L12 regulator (12 V)
FS1	Fuse 250 mA T, 20 × 5 mm
FS2-FS5	Fuses 250 mA F, surface-mount

Opening the case

Acorn points to Appendix E of the A3010 Welcome Guide for removing the top cover; the Service Manual marks the only screws that need removing. Adam Wilson describes the case as held by three clips and three screws. From there, Acorn's sequence is:

1. Pull out the keyboard's two flexi strips from the board and lift the keyboard away. The strips are fragile.
2. Remove the two button-headed hexagon screws under the transformer (metric hex keys) and the two screws at the front of the metal safety case. Slide the case forward 5-6 mm, keeping the floppy drive button pressed, and lift it out of the plastic case.
3. Unplug the two ribbon cables at the rear of the floppy drive and remove the 3 mm hexagon cap screw at the front of the safety case.
4. Slide the upper metal envelope forward until its catches release from the lower one, lift it a little and unplug the speaker, then separate the two halves. The floppy drive is held to the upper envelope by four screws.
5. The board sits in the lower envelope. Unplug the mains cable at the top left by easing back its restraining tab, remove the screw locks on the rear connectors and the ring lock on SK4, remove the earth lead if fitted, and lift the board out.

Backup battery

BT2 is charged from the +5 V rail through D15 and two 180 Ω resistors (R60, R73), and supplies the PCF8583 clock chip (IC5) through R61 when the machine is off. On Adam Wilson's machine the cell had leaked onto the top-right corner of the board, the inside of the lower metal shield and the parallel port.

1. Remove BT2. Adam Wilson cut its three legs close to the body, leaving enough length to grip while desoldering them.
2. Neutralise the residue. The electrolyte of a nickel cell is alkaline, so a mild acid such as white vinegar is used, followed by isopropyl alcohol to remove the salts. Battery Explosion, Capacitor or Corrosion Damage has the full method.
3. Check the tracks and vias around the battery, IC5 and the parallel port for continuity and repair any that are broken.
4. Fit a replacement. Adam Wilson fitted a CR2032 holder with a built-in diode, which stops the board charging the lithium cell; he notes that the PCF8583 accepts a supply of 1 V to 6 V. A like-for-like rechargeable 1.2 V cell is the other option. Battery Refurbishment lists the cells Acorn fitted across the range.
5. After fitting, hold Delete while switching on to reset the CMOS RAM to its defaults; a red border shows that the reset has taken.

Cleaning

• Brush and blow dust out of the board, the transformer area and the floppy drive.
• Clean the rear connectors and the mini-podule connector with contact cleaner.
• The keyboard comes out with the top cover off; disconnect its flexi strips first.

Power supply checks

The supply's figures, from the TRM:

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

Point	Nominal	Notes
TP1	About 23 V	Main secondary after rectification; input to the L4960
TP2	+12 V, 50 mA	Unregulated, fused
TP3	-12 V, 50 mA	Unregulated, fused
LK1	5 V	Main logic rail
LK2	12 V	Regulated 12 V for SCART and the audio hybrid; LK2 isolates it for testing

If the machine is dead, Acorn's procedure (Figure 1-2) is:

1. Check the fuse in the mains plug (3 A) and the board fuse FS1.
2. If both have blown, or FS1 alone, the board needs replacing (in Acorn's service scheme).
3. If only the plug fuse has blown, fit a new 3 A fuse, unplug the mains lead from PL1 and check the lead: earth to live, earth to neutral and live to neutral should all be open circuit (1 MΩ or more).
4. Then check the pins of PL1 on the board: earth to live and earth to neutral open circuit, live to neutral about 5 Ω, the transformer primary. Acorn's text gives about 4 Ω. An open circuit here means the transformer's internal thermal fuse has probably blown.

If a rail is missing, check that LK1 and LK2 are fitted and the drive cables are firmly attached. The TRM warns that the transformer's thermal fuse must not be bypassed; if it fails, the transformer is replaced after the cause has been repaired.

Acorn sized the supply for its own upgrades. The TRM notes a large variation in the current limit of the switching regulator between units, so a third-party upgrade that works in one machine may cause overheating or early failure in another. The interface allowances are 80 mA for the mouse, 50 mA for the joysticks together, 50 mA for video, and 100 mA internal plus 500 mA external for the expansion connector.

Memory links

The A3010's DRAM size is set by links LK20, LK21 and LK22. Set them to match the memory fitted after adding or removing an upgrade.

A3010 DRAM link options (TRM p. 1-20)

Memory	LK20	LK21	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

The Service Manual's check-list before returning a board refers to DRAM size links LK23 and LK24; those numbers do not appear in the TRM's links table for any of the three machines.

Capacitors

All of the A3010's electrolytics are through-hole parts, and none is on the mains side. The full list with Acorn part numbers and positions is on the Acorn Archimedes A3010 Capacitor Guide.

Common failure points

A3010 failure points

Item	Symptom	Check
BT2 backup cell	Settings and time lost; corrosion at the top right of the board	Remove the cell, clean and repair tracks
Supply	Dead machine	Plug fuse (3 A), FS1, PL1 resistance
Supply under load	Unreliable start with large upgrades	Remove upgrades; Acorn's current allowances
Audio hybrid IM2	Crackling sound	Broken hybrid pins, headphone socket contacts
ROM and DRAM links	Dead after a ROM or memory change	ROMs seated in the right sockets with no lifted pins; DRAM size links LK20-LK22 set for the memory fitted (table below)

Tools

• Metric hexagon keys for the safety case screws, and a screwdriver for the ring lock on SK4.
• A multimeter for the supply checks and PL1 resistance.
• Acorn's procedures also use an earth continuity tester, an insulation tester, two joysticks and a TV for the full functional test.
• See Recommended Tools.

Maintenance checklist

1. Open the machine and remove BT2 if it is the original. Clean any leakage and repair the tracks.
2. Check the supply at TP1, TP2, TP3, LK1 and LK2.
3. Inspect the electrolytics around the supply for swelling or leakage.
4. Clean the rear connectors and the mini-podule connector.
5. Reassemble, do a Delete power-on, and carry out the earth continuity and insulation tests.

Related pages

• Acorn Archimedes A3010
• Acorn Archimedes A3010 Troubleshooting Guide
• Acorn Archimedes A3010 Capacitor Guide
• Acorn Archimedes A3020 Maintenance Guide
• Battery Explosion, Capacitor or Corrosion Damage
• Recommended Tools