I know many of you already know this procedure, this post is mostly for the archives since it may not readily apparent how the knobs on the LS-30's come off if you don't have the proper tool that SNK made available for doing so.
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The first thing you need to do, if you don't have the plastic knob removal tool, is to make a little tool to pop out the center cap. What I did was find a piece of heavy wire (I believe the wire below was actually a coat hanger at some point!) in the garage and bent it into this shape:
Then locate the 2 small nubs on the bottom of the joystick handle, this is where you need to use the tool to release the center cap. Just press up (towards the SNK logo on the knob) with the tool to release the tabs on the center cap.
When the cap is removed, you will see a nut in the center of the knob. This nut only needs to be loosened with a 10mm socket. The knob is held on by a compression fitting inside, and loosening the nut relieves pressure so the knob will come right off. If the knob doesn't want to come off, spray around the nut with some penetrating oil (WD-40, Break-Away, etc) as the fitting is likely stuck to shaft from some goo that found its way inside the joystick handle. Let it sit for a couple minutes and try again. The shaft has a knurled end that grips the inside of the compression fitting. It's pretty simple, once you know what you need to do...