Because of the way the wipers are situated, the upper connecting trace is never encountered, but I cleaned it anyway. After a decent (but not extreme) sanding of the upper and lower contact traces, I re-tested the potentiometer and it appeared to work perfectly. None of my cleaners (DeOxit, Ether, alcohol) would remove the oxidation, so I (gasp!) used 1000 grit black oxide sandpaper to lightly sand away the oxidative layer, being careful to not sand down the resistive trace. Not a surprise, given the level of oxidation I observed on the trace - the wiper is sometime able to make good contact, but usually 'floats' over the trace on a layer of non-conducting oxidation. Here, the resistance wildly jumped around from zero to about 2K ohms as I lightly placed my finger on the lever.

When I carefully bench tested the potentiometer, the resistance perfectly matched the other working potentiometers until the very last few millimetres of travel - where the carbon trace ends and the connecting trace begins. What I found was that while the carbon trace and wiper on the linear potentiometer were clean and in good shape, the 'connecting' trace at the bottom of the potentiometer board was covered in oxidation. What I did, however, is completely disassemble the unit, desolder fader 1, and disassemble fader 1 to look at what the issue really was (I previously tried compressed air and fader cleaner and lube to no effect). This isn't really new - many people have pointed this out. I noticed that whenever fader 1 was pulled to zero (completely down), it started 'randomly' jumping around between values, which caused all kinds of other issues (random notes, for example). I started Analog Lab and watched the dynamic feedback as I played and manipulated all sliders, keys, and and knobs.

Last night, I watched my KeyLab stop responding to notes, sending random CCs and then locking up completely. I think I can clear up the many, many threads on KeyLab slider/CC/MIDI woes/random keys/resets, etc.

Key lab 61