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...

A Small Victory...

Seven or eight years ago, we bought a large-screen HDTV. After doing quite a bit of research on the various technologies and models, we eventually settled on a rear-projection triple-CRT model: the Pioneer Elite Pro-620HD.

It's a monster of a TV. If the inside of the cabinet were hollow, you could use it as a residence for 3 or 4 families in some parts of the world.

We've really enjoyed this television. The picture is superb, and the user-tweakable digital color convergence has allowed us to keep it that way for all these years (I adjust it every 18 months or so).

But a couple of days ago it just quit working. The symptoms were not at all encouraging: when you tried to turn it on, the green power light would come on for a fraction of a second, you could hear some relays clicking, and then it just shut down again.

A few minutes on the web and I learned several depressing things: (1) Pioneer no longer supported this prehistoric model in any shape, way, or form (including at their authorized service centers); (2) nobody has any spare parts for it; and (3) there apparently is no longer any such thing as a television repair shop.

I was on my own.

A few more minutes of searching for our TV's symptoms led me to several articles and forum posts. There I learned that this model had a history of exactly this failure – and that at least for one person, re-soldering some “cold” solder joints on the low-voltage power supply circuit board fixed the problem. I also knew from long past experience as an electronics tech that cleaning dirt (especially away from high-voltage components) and cleaning/reseating connectors could often cure a problem.

So I decided to take the back off the beast and see what I could do. The thing was quite expensive, and I didn't want to just throw it away without even trying.

First came the easy part: cleaning off the accumulated dust of years, and reseating the connections. As I was doing this, I could observe (for the first time, actually) all the electronics in this TV. A couple of impressions: it was very nicely made (trust me, not all electronic equipment is!), and there was an awful lot of electronics. I counted 9 circuit boards in the area I could see, and I don't doubt there were more tucked away in parts of the cabinet I couldn't see.

After the cleaning/reseating, we tested. No joy. The symptoms were identical. So I decided to go for the more difficult task of removing, cleaning, examining, resoldering, and replacing the power supply board.

There are actually two power supply boards in this TV: a low-voltage and a high-voltage board. The low-voltage board was the culprit in the article I'd read online, and fortunately it was the easier of the two to get out. The board is mounted vertically at the extreme right side of the cabinet, as you're looking in from the back. There were 17 screws and 11 connectors to remove, and then out it popped. Took only a few minutes to get it out.

Then I took it to our kitchen table, and carefully examined it in the bright sunlight. It was a largish (about 12 x 18 inches) single-sided circuit board with dozens of large, high-power components on it (all of this is typical for a power supply). Right away it was obvious that someone had worked on this board since it was manufactured. The giveaway was that 30 or so solder joints had brown rosin residue remaining – something you don't see on boards that were soldered by machine (the rosin all gets cleaned off with solvents). A little more examination and I saw a pattern: the resoldered joints were larger than the majority of the joints. That led to a theory on my part: that Pioneer had a manufacturing problem that caused cold solder joints on the larger joints on the board (and being a power supply board, it had quite a few of these). Larger solder joints do require more heat, and they are tricky to get right in an automated soldering machine, so this was at least plausible.

So I resoldered every one of the large solder joints on the board – something like 175 of them. The hardest part of this chore was spotting them – my eyes don't seem to work quite as well as they used to. I've done a lot of soldering in my day, and apparently I didn't forget how (it's like riding a bicycle, you know). In the course of carefully looking for each of those large joints, I spotted 3 that looked like they might be cold solder joints, and one definite bad joint, complete with cracks.

When I finished all the soldering, we put everything back together and tried it out. Much celebrating ensued – the danged thing worked, and it has kept on working. Debbie (the primary consumer of TV around here) was very happy to have her TV back, and we were both very happy that we didn't need to go out and buy another TV.

A small victory, to be sure...but it really does feel very good to have had it!