TCL160 Stepper motors glitching / skipping

I posted the other day about my TCL 160 loosing steps but thought i would start a new thread due to eliminating mechanical causes.
I have detached one of the steppers from its ball screw and jogged it off of the machine's front panel and it is audibly glitching / skipping. Obviously this eliminates any mechanical, PC or software issues. I cant see it being the motors, or motor drivers as its happening on both axis and the tool turret.
Im not particularly experienced with CNC machines so could do with some ideas for fault finding. The 3 motor drives are all mounted on a control board so i guess it could be that board or it could be an issue with the motherboard. I also wondered if the drives were getting enough current / voltage? Could this cause it even when the motors are not under and load?
Ive attached a short video, sorry the volume is a little low but thats as high as it goes on my phone.
If anyone has any ideas thy would be gratefully received, i only bought the software for this not long ago and have neither the time nor the money for a retrofit at the moment.

https://youtu.be/fgqfTzHhWOc

Tay - appreciate this can be very frustrating - but no video attached (I think there's a minimum post count of 10 before you can post images - maybe the same limit applies for video). Quick question - would you say that, if you can drive x/z together, that they miss steps at the same instant in time?, or independently? Trying to gauge if this is a common mode fault (e.g. motherboard or PSU).

Hey Doddy, thank you so much for your reply ! That is a very good question, i will give it go and find out tomorrow. This is the link to the video on Youtube, hopefully that might work.

https://www.youtube.com/watch?v=fgqfTzHhWOc