Editing Amstrad CPC 664 Capacitor Replacement Guide (section)

== Diagnostic Procedure ==

# Disconnect the CPC from the monitor (no power).
# Open the system unit.
# Disconnect the floppy drive ribbon at the disc-controller area, the keyboard ribbon at CP002, and the audio sub-PCB ribbon.
# Inspect each electrolytic for visible aging signs: bulged top, leaked electrolyte (brown crust), discoloured sleeve, cracked seal.
# With a multimeter on resistance / ESR mode, probe each electrolytic in-circuit. Good cap: high resistance after charge pulse. Bad cap: low resistance or very high ESR.
# Pay particular attention to the '''470 µF/16 V on the drive +12 V supply''' &mdash; this is the most common 664-specific failure.
# Test the AY output stage: replace C309/C311/C314 as a set if any audio degradation is noted.