Make sure the housing for the switch can move up and down freely (no lose parts/screws and the lead screw is clean and lubed with some light oil). I've had a tactile housing come loose from the lead screw = limit errors - it should be tight with no slop. Go into I/O and see if the tactile switch is working. However, even if it appears to be fine in I/O, many times the switches get flaky. Replace it with a new one. Additionally, if your tactile has a metal plunger on it, remove it, clean it and apply some light oil. Also, I think there is a flag for the up position. Verify it is aligned with the magnetic switch and check I/O functionality. This is all good maintenance but you also need to make sure the driver card is good (maybe the first thing to check!). Look for (smell for) blown cap or burnt wiring on/to the driver. The driver cards can get fried every now and again in which case you need a new one. I don't think you can swap tactile driver card with just any other card. It takes it's own specialized driver but you should double check that if you need a new one as I could be wrong.
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