Ramps 1.4 with external stepper driver on Z-Axis step problem

Hi guys,
I've built a gantry style 3DP that should be able to print 470x400x400mm components.
I used the std Polulo DRV8825 drivers on the RAMPS board, but it seemed that the 1A motor I had was not strong enough to lift the bed.
I then replaced the motor with a 3A 1.8 degree stepper connected to a 2mm pitch lead screw and 16:60 T2.5 belt system.
Mechanical setup: Lead screw dia 16mm, 2mm pitch, 16:60 pulleys T2.5 belt.
1.8 deg/step => 1 rev motor = 200 steps
=> 1 rev motor = 16/60 = 0.2667 rev on lead screw
=> 0.2667 rev on lead screw = 0.2667*2 = 0.5334 mm vertical movement on lead screw
=> 0.5334 / 200 = 0.0027mm per step
=> 1/0.0027 = 370.3704 steps per mm vertical movement

I also increased the current on the DRV8825 to max possible, but the 3A motor would go down and struggle (stop with humm continuing) when going back up.

I decided to replace the DRV8825 with an external stepper driver (Wantai DQ542ma) so that I could increase the current & voltage (now 24V). The connection for the Z-axis was done according to the attached file RampstoDriverWiring as found on the web. This solution works well and drives the bed up and down neatly without any jitters. The problem is that it only moves the axis by 1/2 the physical movement requested. At 370 steps /mm, 100mm requested delivers 49.1. Increasing the steps to 740steps/mm should then fix the problem, but I still get the same results (100mm requested delivers 49.1). Even increasing the steps to 1480 delivers the same result.

Stepper driver dip switches are as follows:
SW1 = ON
SW2 = ON
SW3 = OFF => 2.84Amp
SW4 = OFF
SW5 = OFF
SW6 = OFF
SW7 = ON
SW8 = ON => 1600 pulses/rev

Any ideas what might be the cause of this behaviour?
Regards

... could it be, you have an EEPROM with stored config values? - then the changes in flash would be ignored, until you copy/rewrite them to the EEPROM ...

---

Viktor
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Thanks for the note Viktor.
I checked, but this is unfortunately not the case.
RAMPS jumpers on Z are all NC, thus it should be full step, yet only half the steps are executed.

Ramps micro-stepping jumpers are irreverent when your not using ms1/ms2/ms3 pins on the stepper driver module socket.

Thanks for the note, I understand and it is indeed the case as I also tested it experimentally. The results are attached in the excel file.
What is however baffling me is that:
Why does the system produce only 1/2 the required distance when the required steps are below the Steps/rev dip switch settings on the stepper driver (DQ542ma)?

If the motor was a 0.9 degrees instead of 1.8 degrees, the problem should be resolved when doubling the steps, but it does not resolve problem.
Is there anything else in Marlin or the HW (RAMPS) that could force the system to only execute half the steps?

Weird things happening!
I have been playing with the settings and receive with M503 this extract:
echo: M92 X80.00 Y80.00 Z750.00 E283.00
echo:Maximum feedrates (units/s):
echo: M203 X300.00 Y300.00 Z2.00 E25.00
echo:Maximum Acceleration (units/s2):
echo: M201 X3000.00 Y3000.00 Z2.00 E10000.00
Sending G0 Z10 via serial interface gives me a movement of 5mm, whilst sending G0 Z-10 gives me 10mm movement???
This is very strange to me.
Any ideas what I should look for ?

Send M114 before and after each test move See where marlin thinks it is at