Editing Acorn Archimedes A4000 Troubleshooting Guide (section)

== Boots to the Supervisor prompt instead of the desktop ==

If the machine starts to a text screen at the '''Supervisor''' <code>*</code> prompt (or a BASIC <code>></code> prompt) instead of loading the RISC OS desktop, the desktop itself is almost certainly fine &mdash; the machine has lost its configured startup because the '''CMOS settings are corrupt or have been cleared'''.

* '''To reach the desktop now''': type <code>*Desktop</code> and press Return (at the Supervisor prompt the leading <code>*</code> is optional, so <code>Desktop</code> also works). The desktop loads normally for the rest of the session.
* '''Why it happens''': the setting that tells RISC OS to start the desktop at power-on is held in battery-backed CMOS RAM. A '''flat or leaked backup battery''' loses or corrupts that setting, so the machine falls back to the Supervisor prompt. It usually appears alongside a wrong clock, lost configuration, or the CMOS POST faults (checksum error, or "CMOS&nbsp;unreadable" on a battery-corroded board).
* '''Permanent fix''': replace the backup battery (see the [[Acorn Archimedes A4000 Maintenance Guide]]) so the configuration is retained, then restore a known-good configuration &mdash; hold '''Delete''' at power-on until the screen clears to reset CMOS to its defaults (which re-enable desktop startup), and set anything machine-specific again with <code>*Configure</code>. With a healthy battery fitted, the machine boots straight to the desktop again.

If <code>*Desktop</code> reaches the desktop but the machine still drops to the Supervisor on every cold start even after a CMOS reset, the battery is not holding charge &mdash; fit a new cell.