[lucas]

I finalised the schematic and there are several things wich could be improved but these are not important.
Just one wich confirms the error in the microstepping table: look how the switches 5,4 and 6 are out of sequence with the M1,M2 and M3 inputs. They simply copied the microstepping table from the datasheet wich doesn't match the PCB layout and schematic.

The real error is in the circuitry for idle current reduction, the components wich define the delay are a 2K resistor and 1nF capacitor.
Their time constant is 2 µsec, this means that the drive will go into standby mode approx. 2µsec after receiving a step pulse.

Time to measure the effect of that.
Attached are 2 waveforms measured on the current sense resistors, one is from the Chinese drive the other from my TB6600 drive.
Drives are set for 1/8 usteps, 4 Amp and are driven at 30RPM.
Vertical scale is 0.2V/div. , 1 Amp on a 0.2 ohm resistor = 0.2V so 1 division =1 Amp.
Only the postive part is relevant, the negative part of the waves are a result of the decay mode.

The difference is clear, The wave form should reach 4 divisions for 4 Amp but the chinese waveform goes to 1.2 - 1.3 divisions with some hairy spikes.
These spikes are the 2µsec ones where the drive should reach maximum current after each step pulse.
What we are seeing here is a drive that basically runs in standby mode or 30% of the torque.

I'm thinking of an easy way to compare the torque, a weight attached to a lever seems the easiest.