Sieg KX1 & Mach3 won't come out of emergency reset

[m_c]

Checking the voltages at the board is far simpler than testing each switch individually.
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If the fault re-occurs, measuring to see if the correct voltage is present at the BOB is the easiest and most accurate way to establish if there's a fault in the E-stop circuit. It could be a faulty input on the BOB, but unless you can confirm there is 5V across the relevant pins when the fault occurs, then you're only guessing where the fault is. It could just as easily be a lose connection somewhere.