Help!!! Print extrudes a large blob, and Z axis drops.

[Sraffo 0]

Guys I need help from the collective once again. I have built my own version of the UM2E+ but for the life of me cannot get one print right yet! 

The printer is running of of Tinker firmware (kudos to the genius who created it!!!) but problem has persisted over various firmware updates.

I have been trying to print calibration cubes sliced with Cura & Repetier but every time I seem to have the same problem (the first layer or 2 come out perfectly).

At different stages of the print but normally around the 4-8th layer the printer extrudes a very large blob and then the Z axis drops by 1-2mm or so and continues to try to print.

I am running my bed from a separate power supply through a MOSFET and printing PLA+ at 210degC the print speed has also been reduced.

As per previous suggestions I have reduced the current to all my motors as I initially thought that the drivers were overheating so my X/Y axis is 1000, Z axis 900 & extruder 1000.

I have also changed the extruder motor from a Nema17 x 35mm to a Nema17 45mm @ 0.9 degree steps and have the step count and length completely perfect (had the same problem with both motor versions).

I have fitted a large heat sink and forced air fan to all the stepper drivers but nothing has helped, the heat sink doesn't seem to get overly hot.

Z axis has also been tweaked to move the correct amount IWO steps/mm etc.

Can anyone share some thoughts on what the problem and a possible solution is?

[Sraffo 0]

IMG_1801.zipI have attached a zipped video of the last 50 secs of a print which shows the extrusion blob and the Z axis drop.

I thought a video would speak a thousand words haha.

Hopefully someone knows whats going on and have a possible solution.