X limit switch alarm even w/ no switch connected. Mega V

[shockme]

I’ve just assembled my Mega V. On my first test drive, the homing routine worked fine and I was able to jog the router without issue.
The next morning I had X limit alarms and error messages and the device could not begin a homing cycle.
I can still unlock the Mega V and successfully cut a test file.
On troubleshooting, I find that the impedance of the x limit switch when open measured from the NO connector to ground is only 1.4K ohms vs 2 M ohms for the Y and Z switches.
I’ve removed the switch- by itself it’s now 2M ohms when open. The connecting wires still have 1.4K ohms. Continuing on, I’ve ultimately removed the x-limit wires from the Arduino shield itself. Measuring from the two set screws is still 1.4K ohms vs the same 2M ohms when measured at the Y and Z set screws.

At this point, I believe I’ve localized the problem to either the shield or the Arduino itself having a stray 1.4k ohm connection pulling the pin to ground and triggering the x limit alarm.

Is there more troubleshooting I can do, or am I at the point where I need to ask Millright for a replacement shield and/or Arduino?
Thank you!

[btreichel]

I would re-assemble it and see if you can see it toggle on/off in UGS. BTW, its not unusual to see resistance between pins on an input like that since it is normal practice to use pull-up or down resistors to produce a clean (definite on/ off) signal. 

[shockme]

Thank you for the suggestion! I’ve tried this and as before, no luck. The state of the x limit switch can not be toggled because the controller is sending a continuous “closed” message. This persists even with no switch attached- the Arduino sees a closed switch even though there is none. When the Mega V is unlocked, I can jog the router and cut a project. The status report in each line includes “Pn: X” indicating the x limit switch is closed. Physically closing the x switch had no effect. (Unlike the Y and Z switches which behave as you described)

I strongly suspect that the discrepancy between the measurements 1.4K ohms for X vs 2M ohms for Y and Z is significant and likely explains the problem.

[Bruce]

You can also check if the limit switch LED is lit on the breakout board also. This is a digital input that can be setup with a pull up or pull down resistor which can change the resistance. Typically a voltage level measurement would be a better indicator. +5v or 0v