Extruder won't work, it's neither Driver nor Motor

[firefrog]

Hi there,

I built a Pro W (GT2560 mainboard and A4988 stepper drivers) during the last weekend, and when finished, got it to print initially.
There is a problem with one of the drivers, though, as its Vref jumps from 0 to 0,2 V, then is adjustable from about 0,2 to 0,26 V, and after that it jumps without any transition to 5 V. The seller already sent me a new one that has not arrived yet. I used this driver for the extruder motor, as I thought I'd need that one last, after calibrating all the axes, and it worked quite well, until the driver apparently gets hot and interrupts working to prevent damage, and the motor started to lose steps. Now, that's only the prequel.

Today I exchanged the A4988 driver for a DRV8825 that I got from a colleague at my job who does all the 3d printer setup there. It is new and has never been used.
Now I tried one last time to extrude some filament with the old driver to check for differences with the new driver (eg extrusion length, as the DRV8825 has 1/32 steps), but that's when it stopped working completely. The hobbed gear of the extruder jerked a little forward, then backward, then forward and backward again, and then ceased working completely.
I spent the whole evening checking for errors:

- Checked the cable connection between mainboard and motor
- Checked the fit of the driver on the main board (even changed the driver for the DRV8825, I hope I didn't fry it, as I have to give it back)
- Searched for scorched spots on both the driver and the main board (which is white, good for finding burnmarks ), but no sign of malfunctioning whatsoever.
- Connected the extruder motor to another axis (works)
- Connected the driver to another slot (works)
- Measuring the Vref of the driver on the extruder slot (works as stated above)
- Connected another driver (both the DRV8825 and an A4988 from another axis), does NOT work
- updated the firmware to eliminate software issues (new FW works, but didn't change the problem)


Can you please tell me on what I can check next? Apparently it is neither driver nor motor that is faulty, so how can I check the mainboard? I do not have an oscilloscope or something, just a simple multimeter.

[_kaktus_]

Hi


This may be a non-contact or short-circuit on the controller board near the socket of this stepstick module.
You can test the continuity of connections in this area with a multimeter.

When you find that you think everything is all right, I would consider making a complaint.

I would test additionally, the continuity of power supply to the stepstick module, for both supply voltages.

[firefrog]

Hi Kaktus,

Thanks for your reply. The problem with probing with the multimeter would be that I have no idea about what I can probe and what I can't, because I would fry the board when I did.
Buuuuuut: I got the problem solved otherwise, way easier, as there's one thing nobody tells you: the extruder motor only works when the HE is heated. Now that makes perfect sense for normal conditions, but for testing the extruder calibration, not so much. Still, after somebody on the reprap forum told me, it worked like a charm.

I received the replacement driver today, since then the printer works. It badly needs to be calibrated, and the Z-wobble is still beyond reasoning, but at least it works for now and I can go on.

[_kaktus_]