Editing Sinclair QL Troubleshooting Guide (section)

== Random crashes and lock-ups ==

The QL has a reputation for instability, and much of it is contact-related rather than component failure:<ref name="tfs" />

# Remove all expansions, external ROMs and upgrades and see whether the fault persists.
# Remove, clean and firmly reseat every socketed IC; clean the ROM cartridge edge connector with an eraser on the solder-side tracks. This is a very common cause of crashing.
# Verify the +5 V rail and the regulator's heatsinking.
# Check the machine is to the latest build standard and that the mandatory modifications are fitted.
# Run a thicker wire from the 5 V line at the regulator to the RAM 5 V rail (the thick track running from just above R68 and under IC7) if expansions are marginal.
# Make sure expansion connector pins are straight and the socket is clean.
# Switch all equipment on from one switch where possible, to avoid earth-potential differences between the QL and its monitor.

Where a second working QL is available, swapping all socketed ICs across and then replacing them one at a time is a quick way to isolate the culprit.<ref name="tfs" />