Microsoft Natural Ergonomic 4000 keyboard: fixing non-functional key

2023-01-06 19:43:00

Keyboard membranes

I've been using Microsoft's ergonomic keyboards for close to twenty years now. I've had Comfort Curve models and Natural Ergonomic ones. The Natural Ergonomic 4000 has been my daily driver at the office for years. 

I hated it when it broke down. Or... When literally one of the keys broke down. Every single key on the keyboard worked fine, except the letter "c". It just wouldn't go. Nada. 

Thanks to user teevothis's disassembly video on YouTube, I found the four two screws I never managed to find before.

Opening her up, yes there were quite some crumbs and dust. But nothing overtly wrong. Pressing contacts on the membranes directly worked as expected, but the "c" also didn't work this way. A quick visual check of the contacts for the "c" showed no damage, nor debris interfering with the contact.

Visual inspections of the traces leading to the "c" also didn't show any clear damage.  It did show that the "c" key is at the end of a specific series of contacts, which explains why it's the only key on the whole keyboard that's malfunctioning: something is interfering with its individual trace(s).

There were a few splotches of brown on the keyboard membranes, which suggests I at one point spilled cola in my keyboard. So, I did something scary: I disassembled the actual membranes, which separate into three layers of plastic. There's the bottom layer with traces on top, a middle insulating layer and the top with traces on both sides of the plastic. 

To take the membranes apart, there are four places where the plastic was melted together which you need to carefully destroy. :D A scalpel will do fine, as long as you're very careful. 

I cleaned all three layers, on both sides each, and let'm dry. Putting things together bit by bit: Halleluyah! It worked again!

My hypothesis: some spillage from the cola had gotten into one of the layers of the membrane, shorting the trace for the "c" to its neighbor. Oddly, its neighbor wasn't affected. tags: ,

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