The original part was a NE5230, which is now obsolete, a suitable replacement is a THS4281D or a OPA197IDR
 

I achieved some kind of success in homing the servo motors using the CiA402 home component. There is still a problem when the homing is executed in a certain situation. Basically, I am using homing method 34. Then using the halshow I set  the 'request-custom-homing' pin, the homing procedure starts but when the servo find its Z pulse it start moving quite fast. Perhaps it tries to reach a certain position but LinuxCNC reports 'joint 0 amplifier fault' and the servo drive error is 'Position deviation is too large'. You can see videos of what is happening - one video in normal velocity and one in slow motion.  Videos
This behavior of the drives can be observed the the actual position is above 35 000 000 pulses. When the homing is started below this pulse number, the motor finds it Z pulse and the move quite fast to the position where the homing was started.
Attached are the configuration files.

Thanks again for help. I swapped both analogoutput0 and analogoutput3 to RG58 cable that I had laying around and had the same results. I also double checked the ground and shielding on the original wiring. i had disconnected one of the grounds but reconnecting it also did not change anything.It looks like the oscillation is at about 33Hz so I don't think it is from the main power. Another note, I change the base period on the servothred from 1000000ns to 800000ns to see if that changed anything. it seems to change the frequency slightly but it no affect on the amplitude. 

Yes. First thing I checked is the HAL. This has been a machine that runs daily. no changes whatsoever.

That is exactly what I measured. Disconnected the analog out from the spindle drive, then measured. It's wildly non-linear. What Can I do? I live far away from US and don't really have a way to get a new one too. Can you provide the op amp model so that I can try to fix it?

Spindle drive did emit a bad EMI. I had to put filters in the power line of the PC. But didn't expect it to affect the analog out. 10V power is fed through a separate isolated 10V supply. spindle drive is a 11KW SZGH drive. This worked untouched from 2021 and did run daily without a hiccup. This was the only issue that I ever came across.

I suspect its something with the tachometer emulation or connections to the Fanuc drive

How did the original drive get velocity feedback?

Did you check the the analog command (xx.n.7i76.0.0.spinout) in hal is as expected?
that is 1000 for a 1000 RPM command with a scale of 10000
(in case you have feedback in the PID setup and there is a encoder issue)

If the analog spindle output (when disconnected from the VFD) is non-linear
relative to xx.n.7i76.0.0.spinout pin, it likely means the the OP-AMP buffer
in the analog output circuit has been damaged, perhaps by EMI from the VFD

At lower end it's about twice the voltage, then the error gets lower as we go up. I also noticed spindle rpm glitching once. I have an encoder and had setup spindle at speed with that, That's how I noticed first. Then measured the voltages.