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Acorn Archimedes A4000 Maintenance Guide
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== โ ๏ธ Safety: mains PSU == The A4000 is powered by a separate cased switch-mode PSU inside the unit. The Service Manual is explicit that the PSU must not be opened or repaired: '''do not attempt to repair or modify the PSU''' — exchange it as a unit, because opening it invalidates the safety tests applied at manufacture.<ref name="sm">[[Acorn A3010, A3020 and A4000 Service Manual]], Acorn Computers — hosted on this wiki. Source for the PSU-fail and main-PCB-fail procedures, the 5 A mains fuse and internal fuse FS1, the thermal-shutdown behaviour, the +5 V/+12 V/−5 V rails (+12 V feeds the video connector SK1 pin 12), the functional test suite (ARM250 Dealer Test Disc) and the earth-continuity / DC-insulation safety tests.</ref> After any work, Acorn requires the full earth-continuity and DC-insulation (class 1) safety tests to be re-applied.<ref name="sm" /> * Disconnect the mains lead before opening. The A4000 is unusually easy to open — two screws release the cover.<ref name="chris">Whytehead, Chris. [https://chrisacorns.computinghistory.org.uk/Computers/A4000.html "Acorn A4000"], Chris's Acorns / The Centre for Computing History. Source for the ARM250 integration (ARM2, MEMC1a, VIDC1a, IOC), the "Roadrunner" board (0194,600 Issue 1) being almost entirely surface-mount, the model list (AGC10–AGC82), the Conner CFS105A/CFS210A drives and Citizen OSDA-75G-U floppy, and the easy two-screw disassembly.</ref> * Observe anti-static precautions for the ARM250 and the RAM.
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