Editing Battery Refurbishment (section)

=== Acorn ===

The BBC Master keeps its clock battery in a holder on a lead. The Archimedes and Risc PC range uses two different arrangements: alkaline AA cells in a holder on the 300 and 400 series, and a single rechargeable 1.2 V nickel cell soldered to the board on the later machines. All of them leak onto the board.

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Acorn clock and CMOS batteries'''
! Machine !! Battery !! Location !! Acorn's check or note
|-
| BBC Master series || Acorn's manual describes a lithium manganese dioxide cell, with an optional keyboard-mounted rechargeable battery that the board charges<ref name="mastersm">Acorn Computers, ''BBC Master Series Microcomputer Service Manual'', part 0443,004, issue 1, April 1986, pp. 21–22 (battery back-up of the 146818 clock: internal lithium manganese dioxide battery; optional keyboard-mounted rechargeable battery, charged at about 30 mA for 15 minutes and then 1 mA) and p. 40 (battery connector PL8; battery in its holder next to the speaker; at least 2.6 V at the clock chip with the mains off). Hosted on this wiki as [[:File:Acorn BBC Master Series Service Manual 0443,004.pdf]].</ref> || Holder next to the speaker, on PL8<ref name="mastersm" /> || At least 2.6 V at the clock chip with the mains off.<ref name="mastersm" /> RetroClinic, which sells replacement packs, reports that the packs found in Masters are alkaline AA cells fitted with a diode and resistor, and that alkali from them creeps up the cable to the board connector.<ref name="retroclinic">RetroClinic, [http://www.retroclinic.com/acorn/mbattery/mbattery.htm "BBC Master 128 – Replacement CMOS battery packs"]. Community vendor source for the alkaline packs, leaks onto the case and the board, alkali creeping up the cable to the board connector, and the board charging any connected battery. Retrieved 2026-10-01.</ref>
|-
| [[Acorn Archimedes A305|A305]], [[Acorn Archimedes A310|A310]], [[Acorn Archimedes A410|A410]], [[Acorn Archimedes A420|A420]], [[Acorn Archimedes A440|A440]] || Two LR06 (AA) 1.5 V manganese alkaline cells<ref name="sm300">Acorn Computers, ''Archimedes 300 Series Service Manual'', part 0476,140, issue 1, 1988, p. 6 (specification: "Two LR06 (AA size) 1.5 V Manganese Alkaline cells fitted inside computer main unit. Batteries require replacement once a year."). Hosted on this wiki as [[Archimedes 300 Series Service Manual]].</ref><ref name="sm440">Acorn Computers, ''Archimedes 440 Service Manual'', part 0476,155, issue 1, November 1988, p. 6 (specification), p. 49 (section 6.4.6, configuration, NVM and RTC) and p. 55 (parts list, battery holder assembly 0176,009). Hosted on this wiki as [[Archimedes 440 Service Manual]].</ref> || Holder assembly 0176,009, wired to PL11<ref name="sm440" /> || Acorn specified replacement once a year.<ref name="sm300" /> On the A440, IC16 pin 8 should read about 2.8 V with the power off; if it does not, check PL11, D3 and the cells, each of which should read above 1.4 V.<ref name="sm440" />
|-
| [[Acorn Archimedes A3000 Maintenance Guide|A3000]] || NiCd, 1.2 V 280 mAh, B1, Acorn part 0817,013<ref name="a3000sm">Acorn Computers, ''A3000 Service Manual'', part 0480,050, issue 1, September 1989: p. 32 (the battery is soldered to the PCB), p. 49 (configuration, NV memory and RTC fault finding) and p. 53 (parts list, B1 0817,013 BAT NICAD 1V2 280mAH PCB). Hosted on this wiki as [[Acorn A3000 Service Manual]].</ref> || Soldered to the main board || With the power off, IC6 pin 8 should read about 1.1 V. If it is under 1 V, change B1 and check D2 and C15.<ref name="a3000sm" />
|-
| [[Acorn Archimedes A540|A540]] || NiCd, 1.2 V 280 mAh, BT1<ref name="sm500">Acorn Computers, ''Acorn Archimedes 500 series / Acorn R200 series Service Manual'', part 0486,056, issue 2, June 1991, p. 5-27 (configuration memory and clock fault finding) and p. 6-1 (main board parts list, BT1). Hosted on this wiki as [[Acorn Archimedes 500 Series and R200 Series Service Manual]].</ref> || Soldered to the main board<ref name="sm500" /> || With the power off, IC22 pin 8 should read about 2.8 V; if it does not, check the charge state of BT1.<ref name="sm500" />
|-
| [[Acorn Archimedes A5000|A5000]] || 1.2 V 280 mAh rechargeable cell, BT1<ref name="a5000cd">Acorn Computers, ''A5000 Main PCB Circuit Diagram'', drawing 0192,000/C, sheet 2 (battery-backed RAM and real-time clock), 1991. Hosted on this wiki as [[Acorn A5000 Circuit Diagrams]].</ref> || Main board || Charged from +5 V through D15 and R272 while the machine is on; it backs the PCF8583 clock, IC58.<ref name="a5000cd" /> Acorn's A5000 service manual gives no battery type or part number.
|-
| [[Acorn Archimedes A3010 Maintenance Guide|A3010]], [[Acorn Archimedes A3020 Maintenance Guide|A3020]], [[Acorn Archimedes A4000 Maintenance Guide|A4000]] || Nickel, 1.2 V 280 mAh, BT2, Acorn part 0817,014 ("BAT NI 1V2 280MAH VT PCB")<ref name="a3010trm">Acorn Computers, ''A3010/A3020/A4000 Technical Reference Manual'', issue 1, January 1993, part 2, parts lists: A3010 1M main PCB assembly, issue 3, p. 2-5; A3020 2M main PCB assembly, issue 2, p. 2-23; A4000 main PCB assembly, issue 2, pp. 2-1 to 2-4. Hosted on this wiki as [[Acorn A3010, A3020 and A4000 Technical Reference Manual]].</ref> || Soldered to the main board || The same cell and part number on all three boards.<ref name="a3010trm" />
|-
| [[Acorn Risc PC 600 Maintenance Guide|Risc PC 600]] and [[Acorn Risc PC 700 Maintenance Guide|700]] || NiMH, 1.2 V 280 mAh, BT1, Acorn part 0817,016<ref name="rpctrm">Acorn Computers, ''Acorn Risc PC Technical Reference Manual'', issue 1, September 1994, p. 1-10 (I²C and RTC: "A 1.2V rechargeable cell ... is trickle charged from the +5v supply when the computer is on") and p. 3-1 (parts list, BT1 0817,016 BAT NH 1V2 280MAH). Hosted on this wiki as [[Acorn Risc PC Technical Reference Manual]].</ref> || Main board || Trickle-charged from +5 V while the machine is on.<ref name="rpctrm" /> On Acorn's circuit diagram the charge path runs from +5 V through diode D2 and R130 (180 Ω), with R212 (180 Ω) in the negative lead; the PCF8583 clock (IC20) is fed through R133 and decoupled by C70.<ref name="rpcdrg">Acorn Computers, "Medusa" main PCB circuit diagram, drawing 0197,000/C, sheet 1 of 7 (battery-backed RAM and RTC), 1994. Hosted on this wiki in [[:File:Acorn Risc PC Technical Reference Manual drawings.pdf]].</ref> A board that reports "CMOS unreadable" with a good cell can have a fault in that path: on one 700 board the stardot user philpem found D2 failed, an open via under C70 and a leaking decoupling capacitor next to R133. See [[Acorn Risc PC 700 Maintenance Guide]].<ref name="sd19984">[https://stardot.org.uk/forums/viewtopic.php?t=19984 "(Repair) RISC PC Series 3 (1208,000) motherboard"], stardot.org.uk forum thread, July 2020 to November 2022. Community source: philpem's repair of a 1208,000 board reporting "CMOS unreadable", with 1.3 V across the battery and 0.13 V at the clock chip.</ref>
|}

The 1.2 V cells on the later boards are charged by the board. A common repair is a CR2032 in a holder behind a series diode, so the board cannot charge it.<ref name="retrorr">Retro Repairs and Refurbs, [https://retrorepairsandrefurbs.com/2024/09/27/1992-acorn-archimedes-3010-repair-restoration/ "1992 Acorn Archimedes A3010 repair/restoration"], 27 September 2024. Community source for battery leakage, the PCF8583 clock, track repair and the CR2032 conversion.</ref> The alkaline cells in the 300 and 400 series leak potassium hydroxide, as do the NiCd cells.