Editing Apple II (section)

== Troubleshooting Guide ==
{{main|Apple II Troubleshooting Guide}}
Common issues include display problems, boot failures, and keyboard malfunctions. If the system won't boot, first remove all expansion cards and reseat every chip on the board, then swap chips of the same type to identify failures. For no display output, check the data bus with an oscilloscope for proper signal levels. Bad RAM chips often cause green squares or bars on screen, particularly in the lowest 16K bank. For non-responsive keys, mark faulty keys during testing, then apply 99% isopropyl alcohol with a squeeze bulb at the key stem edges while repeatedly pressing the key. Use the built-in self-test routines and monitor commands for memory testing. Check power supply voltages - the +12V rail should remain above 11.4V under load, and the +5V should stay above 5V. The R/W line should toggle properly; if it never goes low, check the 74LS257 latches at B6 and B7.