[LAD] [Somewhat OT] Strange failure mode of a PC

Hello all, Early this week one of the three 'rendering' PCs of the WFS system in the Sala Bianca failed. It just appeared completely dead and didn't even try to boot when the power button was pressed, but the standby power (for the network interface) was available. I suspected the power supply, so ordered a new one which arrived two days ago. Installed it and things worked again. But now comes the interesting part. While installing the new PS, I also disconnected the wires to the power button, and to test I just used a screwdriver to short the two pins that normally connect to it. But when I reconnected the power button the PC switched off after a few seconds. So it seemed as if the power button was permanently being pressed. I again installed the old PS, and things worked as long as the power button was not connected. Measuring the power button switch with a multimeter showed an unstable resistance value of between 1 and 3k while it was not pressed. So I removed the thing, which turned out to be a cheap miniature switch, a little cube of around 8 mm size. I opened and disassembled it, and noticed that the contacts had some black dirt on them. Cleaned with aceton and reassembled, and things worked perfectly again. What I don't understand is how the contacts got so dirty. If a resistance of a few kOhm is enough to make it look as a closed contact then it can't be handling large currents, so there should not be any arcing. And the construction of the thing is such that it is virtually closed, no dust or whatever could ever creep in. Still it's quite sobering that this cheap 0.30 Euro thing was capable of bringing down a 1600 Euro workstation... Who would suspect a switch to fail in this way ? Ciao, -- Je veux que la mort me trouve plantant mes choux, mais nonchalant d’elle, et encore plus de mon jardin imparfait. (Michel de Montaigne)