Hi Folks,
I've enjoyed reading many past threads here over the years.
We recently bought a 2ndhand Universal M-300. It's 14 years old, but the tube is a 2012 model.
It ran fine for a bit then suddenly started making horrible grinding noises in the Y axis, as if it was a servo fighting to retain its place - except it's a stepper motor.
It would not home properly, and could not be jogged around the bed properly without the machine convinced you'd reached the limits - yet the lens was still in the middle.
X was fine - just Y was the problem.
I eventually found a loose plug on the motherboard and plugged it back in-it looked like an old PC IDE harddrive ribbon cable lead.
However that did NOT fix the problem.
Several reboots and suddenly it behaved-for a day.
The it played up and was no good. Then it came good.
Touch wood it stays that way - today it has not missed a beat.
I've been racking my brain to think of reasons -it's not the stepper motor itself-I changed that out for no difference.
It can;t be the CPU or motherboard... I did re-flash the firmware, and it made no difference.
If it was the cpu or motherboard or the drive on it, I believe it would not fix itself. It would stay kaput.
So I'm down to thinking maybe a possibly weak part of one of the 4 wires leafing to the stepper motor.
Vibrations in use worsen it, and vibrations or a rest, remedies it?

I still have no idea - except that today it's going fine so far!