Author Topic: PMDX416 Limit Switch & Probe Input Wiring Voltage troubleshooting  (Read 339 times)


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Windows 10 64bit, Mach4 PMDX 0.53.263 Firmware 0.60.208 No errors in Mach4.

I am using the PMDX 416 with the PMDX 407 Spindle Speed Controller to drive a homebrew version of the CNCRouterParts 5x10 machine. Using NPN 12v limit switches powered by external supply with the AvidCNC corner finding touch plate. Motion works. XYZ all happen, can drive the machine by jogging, etc. The worst part is this machine was functional in the prototype phase but by moving the electronics into a proper grounded enclosure, using proper wiring and cable management, upgrading the computer, something broke and no longer works.

I cannot figure out why Pins 10-15 are non functional and always are high (+5v). Not sure if the board isn't working correctly, etc. If measure voltage from ground to  +5v on J5 or J7 connectors, I don't get anything, and if I use a jumper wire to jump ground to a pin or 5v to a pin (10-15), nothing changes in the real time monitoring, in the mach status window, etc.. I've enabled them in Mach Settings as inputs, and no dice. What's the best way to troubleshoot this? See attached screenshot of the I/O status to see that the pins are all high.

My current testing (no pun intended) is to enable Mach4 and start things running, jog the machine to verify everything is connected and working, and then start trying to measure voltage across pins etc. All of my output signals in the I/O status window work properly, but i can't get the inputs to show anything. I have tried connecting the probe to +5v and pin 15, gnd  and pin 15, and configured it both active low and high and still nothing.

Steve Stallings

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Re: PMDX416 Limit Switch & Probe Input Wiring Voltage troubleshooting
« Reply #1 on: February 10, 2021, 09:02:08 AM »
The ISO+5 and ISO_GND on J5 are provided by an on board inverter and failure of this inverter or a short on its output could cause the symptoms you describe.

The +5OUT and GND on J7 are controlled by a power management switch that feeds USB power after the unit has completed its power on sequence. This power is not isolated and does not rely on the inverter. It is unusual that your board would be running if this power has failed.

When measuring power you cannot mix connections from the ISO power with the non-isolated power. Both probes must connect to the same power system.

You could check again with your wiring unplugged to make sure that power is not being shorted somewhere in the wiring.

If you still do not have power, you will need to return the board for warranty repair.

Steve Stallings