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Stepper driver Vref not the same after switching to SKR v1.4 Turbo

Posted by CaptainJackas 
Stepper driver Vref not the same after switching to SKR v1.4 Turbo
July 22, 2020 03:08PM
Hi all!

A strange problem came up today when I switched my MKS Gen L for a BTT SKR v1.4 Turbo. For my stepper motors (1.7A) in combination with my LV8729 stepper drivers (R100) I need a Vref of about 0.68V (where the max Vref for this stepper is around 0.75V), so I had set the adjustment screw in the correct position for this (did this a few weeks ago on the MKS Gen L board).

However, after simply switching the stepper drivers onto the new (SKR v1.4) board the value of Vref is now suddenly 0.48V. I tried to turn the screw to increase the voltage but as it already was almost at its maximum I can't increase the voltage any further than 0.55V which is too low for my motors. Does anyone know what the problem could be here and how to fix this?

Note that I ordered 2 BTT SKR v1.4 Turbo boards and the same occurred on both of them, and I also tried this with 5 different LV8729 stepper drivers without any change in result.

UPDATE: So I just tried my DRV8825 stepper drivers and these seem to be working just fine, so it has to be something with the compatibility with the LV8729 drivers as I just checked them on my Gen L board and they're still working fine on that one...

Edited 2 time(s). Last edit at 07/23/2020 07:54AM by CaptainJackas.
Re: Stepper driver Vref not the same after switching to SKR v1.4 Turbo
February 17, 2021 03:28AM
DRV8825 is a fairly difficult technique. So you should be careful to operate it. good luck.
ECJ
Re: Stepper driver Vref not the same after switching to SKR v1.4 Turbo
February 19, 2021 10:15PM
I think it's unfortunate, but SKR 1.4 provides 3.3v instead of 5v to the drivers. The same problem occurs with A4988. I solved this by cutting the VDD pins of the drivers and soldering wires that I connected to one of the several terminals that supply 5v on the board.
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