5i25 to 7i92TM - Spindle Index No Longer Working

Hi Guys,Recently I had my 5i25 card fail and bought a 7i92TM to replace it, updating my HAL file to suit the new ethernet board.
LinuxCNC runs as normal, however, the spindle index pulse is no longer being recognised. The index pulse was detected and rigid tapping worked when I had th 5i25 card installed. I have not made any changes to the HAL file in regards to the encoder.

I confirmed with an oscilloscope the encoder is outputting the index pulse.
Halscope will detect the A and B pulses but not the index pulse.
The index pulse is not detected in either LinuxCNC 2.8.0 nor 2.9.4 (rigid tapping just hangs)

Is there something I am missing in my HAL file or is there a timming error in which the encoder pulse is not being read by the 7i92tm? 

I would first verify that you have the correct firmware installed
in the 7I92T (7i92t_7i76x2d).

Next, I would verify the hardware by setting the 7I76 index input
mode to TTL mode (W4 left), unplug the encoder, then watch
the signal hm2_7i92.0.encoder.00.input-index in halshow
and check that it changes state when you ground the IDX+ input
(TB3 pin 13)

Peter,

Confirmed firmware is correct using latest firmware from Mesa website.

Encoder set to TTL mode and no state change to index-input when idx+ is grounded.

I have confirmed the cable between 7i92tm and 7i76 has continuity on all pins.

Reading other posts with similar issues, I did have an instance when I still had the 5i25 working the cable was loose and cycled the power to the 7i76 ~3-4 times before I picked up on it possibly damaging pin 14. Not sure I rigid tapped at all after this event thought.

As the 7i92tm is brand new, is there a bus chip on the 7i76 I can replace to fix this issue?
While talking chips, I have blown a single input on my 7i76 (older model ~2018), what is the IC part number I need to replace this chip?

The most likely issue on the index is that the encoder differential
receiver (U6 ISL32273) or possibly U13 (74ACT04) have been damaged

On the other 7I76, do you mean 1 isolated input does not work?
This is odd because there is a relatively high power 10K resistor
in series with each isolated input so even a short connection to
120 VAC  is survive-able. It might be a contamination issue.
Perhaps the resistive divider and filter cap for the specific input
could be looked at closely