Saturday, January 8, 2011

A Satisfying Repair...

A couple of months ago, I bought a Das Keyboard (at right) for use at home.  It has the mechanical switches whose “feel” I've long missed.  My typing isn't as fast or as accurate on the modern keyboards with (usually) rubber dome switches.  So I splurged a bit (these things are expensive!).  Within a couple of weeks, the constrast between my keyboard at work and my keyboard at home was unliveable, so I bought one for use at work as well.  I love my Das Keyboards!

But my keyboard at home developed a truly obnoxious problem.  The left-arrow and up-arrow keys (just to the right of the right shift key) started working intermittently.  For a while, they'd work only if the keyboard was tilted toward me (with the top edge higher than the low edge).  Then they stopped working altogether.

I contacted support at Das Keyboard, and very quickly they said they'd never seen this particular problem before, and offered to exchange the keyboard.  That's entirely appropriate support, for which they should be lauded – but it wasn't what I wanted.  Now that I've grown so attached to my Das Keyboards, I was loathe to have to use something else for the few weeks it would take to send my old keyboard back and get a new one in return.

So I decided to try to fix it myself.  I've designed switch-based keyboards, so I'm very familiar with how they work.  There's really not much to go wrong in such a keyboard – it's just switches, diodes, and printed circuit board – any of which I ought to be able to fix.  So to work I went.

The first step turned out to be the most challenging: getting the danged thing open!  I'm not sure I would ever have figured it out if it weren't for this lovely post (thank you, Geoff Breach!).  Thanks to his precise directions, I was able to open my Das Keyboard, and without breaking anything.

The next step was to study the situation.  I had a good clue (what every debugger wants most!): two keys simultaneously failed in the same exact way.  This means it was extremely unlikely to be a key switch problem, as the chance for two of them to malfunction identically was vanishingly small.  It had to be something in common between the two, and that could only be a diode or a printed circuit trace.  It took just a minute or so to figure it out.  In the photo at right (click to enlarge), you can see what I discovered.  The two orange ovals at right show one of the terminals on each of the up-arrow and left-arrow switches: they are connected.  A long skinny trace (highlighted by the arrows) connects them to one terminal on the enter key switch.  The enter key always worked fine.  The problem had to be an intermittent break in that skinny trace connecting them.

A little work with my DVM quickly confirmed this hypothesis.  While measuring the resistance between the enter key's terminal and the up-arrow key's terminal, I twisted and prodded the circuit board.  Sure enough, the resistance varied all over the place, from infinity to near zero ohms.  Somewhere on that trace there must be a hairline crack (so thin I couldn't spot it, even with a magnifier).  So I tried a brute-force repair: I soldered a piece of hook-up wire between the two terminals.  Voila! I reassembled it all without difficulty, and now my Das Keyboard is now as good as new.

I haven't the words to describe how satisfying it was to be able to troubleshoot and fix this.  Silly, I know, but true nonetheless.  Note that in the process of repairing it myself, I violated the terms of my warranty, so now my keyboard is truly mine.  I'm sure the Das Keyboard folks would sternly disapprove.  I'll tell them anyway, as they may be interested to know of a potential manufacturing quality issue...

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