The CPC keyboards contain fragile keyboard membranes, which have a rather low lifetime of maybe 5-10 years. Pictures of the membrane are here: CPC6128 Keyboard Disassembled.
The east-german CPC clone KC Compact Computer contains a more robust real keyboard circuit board, which should give it an infinite lifetime.
Repair
There is no chance to repair broken wires on the membrane by soldering (either the wire vaporizes, or the foil melts). However, one can repaint broken wires using conductive silver, which is sold as:
- English: conductive silver (or conductive paint)
- German: Leitsilber
- French: ?
- Spanish: ?
the silver should be available anywhere were you can buy electronic components. It may be also available as car equipment (for repairing the rear-window heating).
Replacement
New Membranes
New membranes are available for other home computers. But none are sold for CPCs...?
Adapters for PC Keyboards
The CPCKey circuit translates the serial PC Keyboard signals to CPC keyboard matrix signals (the circuit uses a lot of components though). A simplified solution may be a single chip with built-in microprocessor, flash memory, and I/O ports.
Rewired PC Keyboards
Cut all wires on the circuit board, and rewire them as in the CPCs keyboard matrix. Sounds simple, but it's quite a lot of work. Of course it works only with keyboards that do have a real circuit board (eg. many inexpensive noname keyboards use boards), not with membrane based keyboards (eg. the infamous overpriced Cherry keyboards).