@Shoki To add to what @dc42 said, a 1K ohm pullup should give a voltage of around 4V for the signals. This should be enough; the TB6600 datasheet has the input voltage on CW/CCW, CLK, and ENABLE (as well as other pins) as between -0.2V to 0.8V for low, and between 2V to 5.5V for high, which explains why 1.4V doesn't work, but 4V should. See top of page 5 here: https://www.mouser.com/datasheet/2/408/TB6600HG-483084.pdf
I think you have an MKS TB6600 board. The files for this are available here: https://github.com/makerbase-mks/MKS-Big-Current-Driver/tree/master/MKS TB6600-Black
There are some resistors on each input that can be seen in the schematic, labelled R6, R8 and R9, but unfortunately they don't list the values of components.
https://github.com/makerbase-mks/MKS-Big-Current-Driver/blob/master/MKS TB6600-Black/MKS TB6600(Black) V1.1_001/MKS TB6600(B)lack V1.1_001 SCH.png
Ian