Editing Maintenance/Mouse button replacement (section)

== Nothing to lose but our chains ==
[[File:Scattered screws.jpg|thumb|So many screws]]
Time to go deep.  Take apart the everything and find out what I broke.  I'd rather leave the switches in place, they seem good enough mechanically and I'll probably just tear away the remaining traces if I touch them again.  Instead, there's got to be a way of rerouting the signals that went to the missing surface-mount pads.  A continuity tester confirms that the other working buttons do what we might expect: one side has a positive voltage and the other side causes a wire in the board connector to toggle between high-impedance and positive reference.  The broken buttons don't cause a similar signal anywhere on the board connector, and it's hard to follow the traces because of the high-security board layout and black solder mask.

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[[File:Mouse confidential board.jpg|thumb|left]]
<big>Oh, hold everything!  The middle board is clearly marked "confidential", we'll have to stop here because it's simply not allowed.  (I jest.)</big>

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[[File:Two layer board.jpg|thumb|Two-layer board edge]]
Looking at the edge of the PCB shows that it's only two layers so everything that happens is on the front and back.  Electrical networks can only cross through the board via a via, go sideways along a trace of foil, or through a component.  Nonetheless, I can't quite follow the signal.  Now we're going to have fun: I make a test jumper ending with a small resistor to avoid a high-current short, clip it to the positive reference voltage on a working switch, and poke this into each conductor of the board connector one at a time with the mouse powered on.  Xev begins to reveal the confidential secrets.

Luckily for me, this is successful!  It becomes clear which of the switch pads should carry positive voltage and which board connector wires relay the outgoing button signals.
[[File:Mouse final jumpered top.jpg|thumb|Top jumper|left]]
[[File:Mouse final jumpered back.jpg|thumb|Bottom jumper]]
In the end it only takes two additional wires to make the mouse fully functional.  Photos are included for your amusement.  The top jumper looks especially scary since it attaches to an unusual hole cut in a ribbon cable, but both wires make me slightly queasy.

I would file this hack under the "I'll jam the satellite uplink with my hair clip while you break into the broadcast station with a chainsaw" school of electrical engineering, and the resulting monstrosity is a fire hazard without a doubt.  I wouldn't feel comfortable letting anyone else use it.  But it's good enough for me!

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[[File:Mouse is patched.jpg|thumb|Empiricism rules.|left]]
<big>Here's a close-up of the most absurd detail, where I scraped away at the ribbon cable insulation to more easily patch in—kids, please don't try this at home.</big>

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