This is a short article on a lighter note.
I got a broken keyboard (from boxes with DOA stuff) with a few keys that were not working.
I've opened the keyboard up and marked the keys that were not working, you can see a slight red marker trace in the picture below:
The key circuitry is a sandwich of three flexible plastic layers: top and bottom with conductive traces and a middle one for isolation. Only the bottom one was broken.
Using a continuity meter the breakage was traced to an area near the connector.
As a heads-up, the measured resistance for this type of traces is 5-10 ohms/cm, so for a strip/trace longer than 20 cm the meter might not beep anymore.
I had some silver paste sitting around unused, so I covered the broken traces with that.
...after shaking all the silver flakes/powder should be evenly distributed. I don't think they mention this anywhere.
I believe a bottle of that stuff is around 15E for 5ml, but should last a really long time.
There's no way to properly construct traces, I've tried using toothpicks and other small-pointed objects:
I've left it to dry for 5 minutes then proceeded to remove the large unneeded areas with a cotton ball tip and traced the outline with a needle-like tip:
After 30 mins of drying and some more cleaning the keyboard was ready for use.