It’s easier to access the magnet if you take the black plastic bumper off first. There are four 10mm hex bolts towards the back and four philips screws to take the pickup head off the front.
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Everything Robotics
Everything Robotics
That magnet sensor is clearly a weak point in the robot, and I would advise any user to brush it clean and oil it when overwintering.
HA! I repaired mine with fitting it with a small rare earth magnet. The magnet wanted to settle midway between the zip tie and the end of the "sort of stick with a magnet". So I left it there and it worked!
BTW, what does the magnet do? Does it feed back to a sensor, that it has been moved?
I have exactly the same error. I whished you would show us the HD magnet, and how you mounted it.