Fixed: surface mount microsurgery on DSi game console

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My buddy, C, had a problem with his Nintendo DSi handheld game console: the shoulder buttons, after many many thousands of cycles, had failed.  C is a big-time Flipnote animator on the DSi and without the index-finger-action of the shoulder buttons, animating gets way less fluid.  Buying a replacement seemed unnecessary because I was pretty sure that the fairly inexpensive tactile switches (new and old, bottom right) inside had failed and could be replaced.  What I didn’t count on, was that the switches were only 3mm wide

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Unlike some other Nintendo devices, this one didn’t require the non-standard tri-wing screwdriver.  A very small Phillips screwdriver was all that was needed, so props to Nintendo for that design decision.  After flipping the device over and pulling the battery, I removed 8 screws, including one in the game card slot, 2 under the adjacent rubber plugs, and…

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one hidden under the label in the battery compartment.  You could call this screw the tamper-evident warranty voider.

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Happily there were no snappy clips that you often find holding consumer electronics together and that are so prone to breaking off.  The lower shell came off without a hitch, and I was careful to unplug the unnerving copper coloured flex cable that runs to both buttons, connecting them to the mainboard mounted in the top half of the shell.

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Here’s the left shoulder button.  L-shaped PCB (centre) is upside down, and where I expect to find the troublesome tactile switch.  Spring return for the larger button (top) that pushes the switch on the PCB, and pivot point for the button at upper right.  I’ve got to pop this PCB out of it’s hole, flip it over, and secure it so I can replace the switch.  Now here’s the freaky part: doing this requires pulling, bending, unfolding the flex cable.  Flex cable is really just conductive paint on plastic ribbon, and it’s been used in all consumer electronics since we stopped using honest to goodness wires to connect sub-components 30 years ago.  As any maker knows who dares to tread in this domain, you can break/tear/render-useless flex cable by merely looking at it 3 times.  And when it’s broken, you are in a world of non-repairable hurt. 

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To illustrate the point, here is the push-connector that joins the two halves of the DSi.  This connector is only about 7mm long and has 13 connections per side leading to hair-thin traces.  So you need to plan ahead like brain surgery, note the origami folds of the cable so you can reassemble the device, keep the sharps away, and handle it as little as humanly possible.  This patient was lucky, and livedMany others A few in the past weren’t so lucky.  Not trying to dissuade the DIY crowd here, just trying to explain why I decline to help friends swap the LCD in their $1200 cameras or replace the non-replaceable batteries in their iPhones.  I waived my usual “let’s understand it’s already dead” disclaimer with C when, drunk with optimism, I said “This should be pretty straight forward.”

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Popped out the right PCB as well, and after doing so, I taped up the push buttons so the springs would not inadvertently be sent flying into the netherworld that is the floor of the lab.

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Here’s the old left switch.  The Canadian nickel for scale, looks about the size of a hot tub compared to the switch.  To remove the old switch, you can try pouring the heat to it with a soldering iron and try to pluck it off.  Not too long ago, I catastrophically ripped up some board traces using that technique while hacking a wireless camera.  With higher stakes this time, I decided to try…

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Chip Quik.  My buddy, dmay, put me on to this years ago as a great way to remove SMT flash chips from boards, but I never picked up that ball until now.  You can get a kit of this stuff with the tacky flux in the tube, the low-melting-point solder alien alloy, and some alcohol wipes for flux cleanup.  Only $16 + $8 shipping from the massively awesome Digikey who will have your parts at your door the next day if you order by 8pm.

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I used a toothpick and smeared some flux around the 5 PCB contact points.  Then, I went around the switch with the soldering iron and the Chip Quik alloy, and bob’s yer uncle, the switch came right off.  Like magic.  Apparently, the alloy has a much lower melting point than the tin/lead solder used to originally make this device.  Flowing the alloy under the switch mixes the metals, allows the whole mess to stay molten longer than straight solder, allowing the old switch to easily be removed.  I was a sceptic, but now I’m converted.

With the old switch off, I used some 1.5mm solder braid (above) from Deal Extreme for $1.89 to clean the pads of this Chip Quik + solder mess, leaving pristine pads that I wiped down with alcohol.  Here I stuffed a piece of scrap FR4 under the switch PCB so as not to damage the DSi plastics.  Also note the green painters tape I use to rig up lots of stuff on the bench.

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The replacement switches are also from Deal Extreme, for $0.75 each with free shipping.  I threw in a $3 DSi replacement battery as well, since C has had the DSi for a couple years.  I’m a DX junkie and buy stuff there all the time.  It takes 3-4 weeks for the delivery from China, but shipping is free and gear/parts are dirt cheap. 

Installing the new switch was as easy as fluxing the PCB pads, pushing the new switch into place in the tacky flux, and then using good old tin/lead solder to… screw it up.  You can see above that I’ve bridged the solder between the centre and left pin on the bottom of the switch.  Bad.  This is all so small that I sort of turned off my targeting computer and used The Force to solder it.  Then I taped a plastic magnifying lens over my Z10 camera and shot this so I could zoom the photo and see how I did.  (Most of these pics shot the same way, with a bit of post-pro in Lightroom)

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For this microsurgery, I’m using hair-thin solder (above) that is flux core and only 10/1000 of an inch thick.  But even with skinny solder, if you feed enough in, you’ll get undesirable bridges.

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Not to worry.  I used the Chip Quik again, pulled off the bridged switch, and installed an extra new switch.  Another camera shot (above) showed the solder a little thin on the pads, so I hit it again with more solder…

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and then it looked it looked electrically and mechanically sound.

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More flex cable origami, closed up the two halves of the shell, screwed the screws (taped down here to prevent escape)…

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and had C fire up the console.  Boom!  Working!  Happy day.  Good to be back in the lab a bit.  Inspires me to make some necessary pole-cam mods tomorrow.

Happy making,
DW

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