Editing Acorn Archimedes A3020 Troubleshooting Guide (section)

== Video faults ==

A very common "dead" report is actually a '''monitor-type mismatch''': POST sets a 15 kHz mode, so a VGA or multisync monitor may show an unsynchronised or blank picture at power-on even though the machine is healthy.<ref name="stardotvideo">[https://stardot.org.uk/forums/viewtopic.php?t=7578 "A3020 no video / monitor type"], Stardot forums.</ref>

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Symptom !! Probable cause !! Action
|-
| No picture, machine clearly boots (floppy/sound active) || Monitor-type mismatch, or monitor/cable || Try a 15 kHz/multisync monitor; force the monitor type (hold '''Delete''' at power-on to reset CMOS, then reconfigure)
|-
| No picture, machine does not boot || Logic/PSU fault || Use the power and dead-machine procedures above
|-
| Corrupt or striped display || DRAM fault || Run the memory test; a single failed device gives a repeating pattern
|-
| Wrong or shifted geometry only || Monitor adjustment / mode || Not a board fault
|}

The analogue RGB output is 0.7 V peak-to-peak into 75 Ω at the 15-pin video connector; if the machine boots (confirmed by disc and sound activity) but there is no output at the connector, suspect the VIDC section of the ARM250 or the video output components.<ref name="trm" />