7i76e - Input pin erratic behaviour

Context: An old Boxford 160 lathe adaptation, using the (fabulous) Mesa 7i76e card (integrated FPGA/2-port/massive break-out of I/O/Steppers etc). Started too many years ago and been through various incarnations, LinuxCNC uplifts etc. Never really used in anger, but more for learning about LinuxCNC, in between juggling work, the wife and various cats. Now that I'm retired I can start to concentrate a little. A long winded way to say I think it used to work but now...

Somewhere along the way something has happened. I have push button controls for jog x+/x- and z+/z-, with the jog speed controlled by an analogue pot, From memory, this all worked. Then retirement hits and I get more time to play. The behaviour now somewhat peculiar. X+/- work as expected. Z+/- are more erratic. Turns out, through HAL-Show/Scope that I have z+ on 7i76e.0.input-08 and z- on 7i76.0.input-09.

If I activate (field voltage to input) input-08, the resulting waveform on halscope shows an erratic 0/1 value for the duration of the field voltage being applied. Once field voltage is removed then the signal on halscope reverts to a steady 0.

If I apply field voltage to input-09, then input-9 is shown high on halscope and input-8 reverts to the erratic 1/0 value whilst the voltage is applied to input-09. Removing voltage from input-09 and both input8/9 on halscope revert to 0.

The observation on halscope describes perfectly the observation on the machine - traverse in the Z axis is erratic to the point of occasional reverses of direction and/or stuttering of the jog.

Particularly as my fuddled brain thinks that when I last played with this this all worked, I'm thinking this is likely to be a hardware issue on the 7i76e card. I've quickly belled-out all other inputs and they appear to work as expected. This does mean I can re-wire to use an otherwise unused input, but this irks me.

Has anyone experienced anything like this before?, and is there a solution (e.g. a different bit-file for the FPGA?)

The nature of this is peculiar to my mind, that this is likely tied not so much to a IP fragment of the FPGA, but more likely individual hardware between the terminals on the board and a FPGA port pin. Particularly as the input-8 looks to be in someway coupled to input-9 I'm inclined to get the associated pins under the microscope and reflow the joints, but that's a job for another day. This post just to understand if anyone has witnessed similar and found a solution?

Regards,

Mike

Kind of where my thoughts where - to the periphery of the board the wiring is correct - I've strapped field-V to the inputs (input KEFG connector). What you've described I can believe with a broken track/open circuit component on the board.

Yes, coupling of inputs often means a missing ground.

Note the the field I/O is completely isolated from the
logic (5V side)