Editing Acorn Archimedes A4000 Troubleshooting Guide (section)

== First steps: power ==

Most "dead A4000" faults are in the PSU or its feed, so confirm power before anything else.<ref name="sm" />

# Switch off, unplug the mains lead.
# Check the '''5&nbsp;A fuse in the mains plug'''. Fit a new 5&nbsp;A fuse; if it blows on switch-on, the PSU is faulty &mdash; exchange it.
# Check the internal fuse '''FS1'''.
# Measure the rails at the PSU-to-PCB connector: '''+5&nbsp;V''' (logic), '''+12&nbsp;V''' (video connector SK1 pin&nbsp;12 and the disc motors) and '''&minus;5&nbsp;V'''. A single missing rail points to the PSU.
# If the PSU runs briefly then cuts out, suspect '''thermal shutdown''' (check ventilation and the load); repeated shutdowns mean a faulty PSU.

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:90%; text-align:center;"
|+'''A4000 supply rails'''
! Rail !! Feeds !! Note
|-
| +5&nbsp;V || Logic (ARM250, RAM, ROM, I/O) || Main logic supply
|-
| +12&nbsp;V || Video connector SK1 pin&nbsp;12; floppy/HD motors || Disc + monitor feed
|-
| &minus;5&nbsp;V || Analogue / video || Low-current rail
|}