Z motors repeatedly interrupted

Hi

I have a pretty odd problem. I have an elderly Mendel fitted with RAMPS 1.4 which has been out of use for a while, so I decided to give it a clean up and get it going again. As part of this I decided to upgrade the Marlin firmware, Slic3r, Pronterface etc.

Now the printer basically works - except for this issue affecting the Z motors*. Basically I can connect, move XYZ no problem but shortly after homing the Z motors begin to "tick" every second or so... it feels like they are being de-energised for short pulses. If I move the Z axis it repeatedly pauses, sometimes it squeals when it tries to restart.

The X & Y axis don't suffer - in fact they are quite happy moving while the Z axis is stuttering away.

I've used v1.1 and the latest bugfix. The old v1.0 is OK though.

Any ideas? I can put the old version back, although I'd like to update it if possible.

* Dual motors, but in parallel with a single driver. Also I don't have auto leveling enabled FWIW.

Ticking is normally the vref is to high and the stepper drivers are shutting down to protect themselves, over and over.

That's it, thanks! Obviously the firmware upgrade was a great big red herring then.

Turning the stepper current down a bit stops the shutdown. So it looks like next job is to add some cooling to the boards and check the driver currents (no idea how they're set up as I bought the printer secondhand).

Regards

For Pololu drivers: [youtu.be]