Editing Acorn A5000 Maintenance Guide (section)

== Power supply checks ==

The PSU is a self-contained fan-cooled module. Start with the Service Manual's "action if PSU fails" routine:<ref name="sm" />

# Switch off and unplug the mains lead. Check the '''5&nbsp;A fuse in the mains plug'''. If a new fuse blows on switch-on, the PSU is faulty.
# For an individual rail failure, check the rails at the faston power connectors: '''+5&nbsp;V''' (main PCB, floppy, hard disc), '''&minus;5&nbsp;V''' (backplane), '''+12&nbsp;V''' (video connector SK1 pin&nbsp;12, and the disc motors).
# If the PSU runs then shuts down, check the fan and the fan aperture; a failed fan or blocked aperture causes thermal shutdown. Repeated shutdowns mean a faulty PSU.

A faulty or ripple-prone PSU is recapped; Acorn's original exchange-only advice assumed spare modules that no longer exist. '''⚠️ The PSU primary side and its reservoir and mains-suppression capacitors can hold a lethal charge after the machine is unplugged &mdash; a shock can be fatal.''' Only open the PSU if you are competent with mains switch-mode supplies, and '''discharge the reservoir capacitor and confirm 0&nbsp;V with a meter before touching the primary side''' (procedure in the [[Acorn A5000 Capacitor Guide]]).