Editing Acorn Archimedes A4000 Troubleshooting Guide (section)

== Mains warning — risk of fatal shock ==

The A4000 has a mains-powered switch-mode PSU inside the case. Its primary side and its reservoir and mains-suppression capacitors '''can hold a lethal charge even after the machine is unplugged''' — a shock from them '''can kill you'''. '''Disconnect the mains lead before removing the cover,''' and never work on the supply while it is plugged in. The PSU can be opened and recapped as part of a restoration, but only if you are competent with mains switch-mode supplies: discharge the reservoir capacitor and confirm 0&nbsp;V before touching the primary side (see the [[Acorn Archimedes A4000 Capacitor Guide]]). Re-apply the earth-continuity and DC-insulation safety tests after any internal work.<ref name="sm" />

[[File:Acorn Archimedes A4000 circuit diagram (1 of 3).png|center|thumb|680px|Acorn A4000 "Roadrunner" main PCB circuit diagram, sheet 1 of 3 (Technical Reference Manual), showing the ARM250, the battery-backed RAM/RTC, reset circuitry and the filtered +5&nbsp;V supply. Sheets 2 and 3 are also on the wiki. (Source: The Centre for Computing History.)]]