Editing Amstrad CPC 464 Maintenance Guide (section)

== Keyboard Maintenance ==

The CPC 464 keyboard has a layered construction: '''hard plastic keytops''' (or flat keys on revisions 1+ where the keyboard ribbon connects through CP002), '''silicone rubber domes''' (parts 170008/170009/170010), and a flexible '''membrane contact PCB''' (parts 170028/170029).

Common keyboard faults:

* '''Whole row dead''': membrane trace broken or contact PCB-to-main-PCB cable fault. Reseat the cable; if the row remains dead, check continuity along the membrane track for that row.
* '''Single key dead''': dirty contact. Open the keyboard, clean the relevant carbon pill on the silicone dome and the matching pad on the membrane with IPA on a swab. Do not abrade the carbon pill &mdash; it is conductive coating, not metal.
* '''Single key permanently active (stuck)''': membrane shorted, often by an old liquid spill that crystallised between two adjacent traces. Clean the trace area with IPA. If the short remains, isolate the trace by carefully scoring the membrane between the two adjacent pads &mdash; this is a last resort.
* '''Soft keys / no click''': silicone dome collapsed. Replace the dome from a donor keyboard; modern silicone replacement sets exist on the after-market.

The CPC 464 has no key matrix scan code reported in the BIOS to identify a stuck key (unlike a PC). The classic diagnostic is to type a known sequence at the BASIC prompt and look for additional characters appearing.