When the chance arrived to buy a mechanical keyboard for not a lot, naturally, [Hales] jumped at it. Then it started having odd intermittent problems with some keys appearing stuck, which led to a teardown and some fault finding. The culprit was a white LED — but why this was the case is a fascinating story.
Stripping it down there didn’t seem to be an obvious culprit, but eventually, the trail led to a lack of diodes in the matrix. This keyboard had an extremely clever yet rather cursed design in which it used LEDs as both illumination and as a diode in the keyboard matrix circuit, and the faulty LED had a reverse breakdown condition that could be triggered under certain operational conditions.
More unexpectedly, it would sometimes hold on to its reverse breakdown state even after power off. Just when you think you understand a component’s properties, there’s always room for surprise. And we can safely say we’ve learned something about the design of cheaper keyboards in reading the account. It’s clear that when it comes to ‘boards, it’s best to take no chances.