Wondering where to find the circuit diagram of the actual keyboard matrix (i.e. positions on the rows and colums where the common schematics http://www.x-speed.de/computer/amstrad/schaltplan_cpc_464.gif ends with the words KEYBOARD CONNECTOR), and just when about to ask around here, I stumbled upon the long-lost CPC 6128 Service Manual at http://safemanuals.com/user-guide-instructions-owner-manual/AMSTRAD/CPC%206128-_E featuring this piece among all the information we wish we'd had a quarter-century ago...
Wow, thanks for the link.
Found the same 6128 manual but a different (15mb) scan:
http://safemanuals.com/user-guide-instructions-owner-manual/AMSTRAD/CPC6128-_E
Also the 464 manual (15mb):
http://safemanuals.com/user-guide-instructions-owner-manual/AMSTRAD/CPC464-_E
Hey, how about http://www.cpcwiki.eu/index.php/Service_Manuals then? :D