The 5V on the Gen6 board is oscillating at approximately 23kHz.

This oscillation is caused by a much to low phase margin. The PWM controller is not designed for a ceramic output capacitor. The ESR of the ceramic capacitor is to low.
On my board the oscillation amplitude was approximately 300mVpp.

This oscillation causes problems with the temperature measurement. Also the current through the stepper motors is influenced by this oscillation.

I did an openloop simulation with LTSpice to see how we can fix this oscillation

By adding a 1nF capacitor parallel to R12 the circuit is stable. The phase margin is much higher. (Not optimal but this should include more changes)
I soldered a 1nF/0805 capacitor on top of R12. The oscillation is completely gone.

The temperature measurement is now rock stable. (Even with klimentkip firmware without filtering)
The motors are now silent (Unless they move of course)

Hi, is this problem likely to be on all Camiel's Gen6 boards? Can you post a picture how you did this? I haven't got as far as wiring up the temperature sensor, but in testing I do have whining motors, particularly the X and Y axis when they are on hold. And they get quite warm while on hold.

I'm interested in seeing what you did too...

but fwiw, stepper motors get warm when on hold.. that's how they work... they draw their maximum current when on hold.. and less as their RPM increases.

Al...

Hi Erik
Is this mod still working for you? Can everyone do this mod, or do is it specific to each board? Can you give me a bit more information about the capacitor you used? There are a lot of variations of the 1nF-0805 capacitor, and I don't know too much about electronics.

I finally got around to doing this mod, which is quite tricky as you need to solder one tiny SMD resistor on top of another. However, the results were immediate; temperature reporting is now very stable, and no appreciable whine from motor or heater drivers. Thanks Erik! And thanks a second time for Marlin!

A bit of extra info on the mod here: http://forums.reprap.org/read.php?181,93663

Just a friendly note that I performed this fix, albeit with a 0603 100nF capacitor instead of the suggested 1nF. It seems to be working well; the machine is near silent when all axes are homed and much quieter in general. I haven't had much of a chance to test the other benefits of it, but I suspect they are present as well.