Zonestar Extruder motor does not work - what can I check? While this may seem like terribly noobish question, I'm sure one day someone will have same problem.

I own a ZONESTAR P802QSU (Bowden extruder) and all of sudden my extruder motor stopped working. What I did:


I check whether or not motor is moving freely - I can rotate it without any problems manually.
I checked out cable and plugs - everything seems OK.
I checked whether motor is working after plugging it into another slot in motherboard - motor works fine.
I checked if another motor works after plugging it into same slot on mainboard - and it does not.


It would seem that there is something wrong with E0-mot driver module, or with socket. I'm however totally at loss about what can I do with any of those. I do not have any electronic equipment except multimeter, and voltage on motor seems fine(11.3V between red and black, I guess V+ and ground). It sometimes seemed to get lower, but I'm almost sure it is my trembling hands.

After some googling, I started checking A4988 stepper driver with my multimeter. VDD was ~5V and VMOT around 12V, so it seems to work at least in this way.

What can I do, to see what is broken? Visually nothing looks like it burned out, but I'm fully aware it may not be visible.
Good investigation there!  You are almost certainly correct that a driver chip has gone blooey.  Personally I doubt it's worth the effort to locate and repair, rather than buying a new, trustworthy board.  

I recommend this approach because one blown chip may well have caused (or been caused by) unrecognized damage elsewhere, which might then lead to future failures.