Coca Cola ate my keyboard

There's a lot of mythology out there about the corrosive properties of Coca Cola. Most of it is hooey; the corrosive effect is largely exaggerated, but not entirely. Someone spilt some coke on my keyboard and the syrup, over time, ate through several of the copper traces on the PC board under the keys. As a result a couple of the keys stopped working altogether and I had to break out the soldering iron. Don't know that anyone cars, but here are some pics of the repair.



Here we have a nice picture showing the "hammers" of the weighted action. Each hammer consists of a piece of heavy wire of different lengths, the heavier and longer wire hammers corresponding to the bass registers. Electronic keyboards usually have small, light keys with little of the feel of a conventional piano's action. There's a place for them in the instrumental cornucopia, but I've never liked them. Mine is a so-called "electric piano" which has a full-sized keyboard with individually weighted keys to mimic the feel of an acoustic piano. I would have it no other way.

I like this picture because it shows how the electronics figure out how hard you press the keys to control the volume of the note. Super-cheap keyboards play notes at the same volume irrespective of how hard you press the keys. I used to think perhaps they accomplished the volume-sensing feature by utilizing a piezo-electric sensor or the like, but it's really so elegantly simple, I feel stupid for not having thought of it before. The velocity at which the key is pressed down is sensed by measuring the time interval between the closing of two switches. In the picture, they are the pairs of black dots seen on the orange rubber membrane. The switches are places one behind the other in such a way that they close in succession as the key approaches the bottom if its stroke. The faster the key is traveling, the faster the key will traverse the small amount of travel between the first and second switch. There you go.

The switches seen in the picture above are really just carbonized patches of rubber than contact the exposed traces shown in the picture to the left (black horizontal lines arranged in rectangles along the bottom of the PCB). What happened is the coke syrup settled on the thin traces shown at the end of the orange and red jumpers furthermost left in the picture. Eventually, this broke continuity along a couple of those traces and I had to jumper them as shown.


And that's pretty much it. Good as new.