Thanks for your reply!
Indeed, the hall-sensor cables have been repaired, as i also suspected them from being broken.
As this didn't help, i also took away the plastic potting around the pcb and did a proper continuity-test on those cables, that all seems ok.
But, after your reply i went to the next step and tried to measure the hall-sensor as described here:
https://endless-sphere.com/forums/viewtopic.php?f=3&t=105444&p=1543436&hilit=led+hall#p1543566
In short, i've placed 5v+ on the red wire, and GND on the black wire.
Then, through a 10K resisor, i applied the 5v also the my red measurement probe, and connected the black measurement-probe to GND.
I then measured the blue, green and yellow wire individually whilst rotating the motor axle.
Interpretation of the result is not very clear to me, it seems like the yellow one gives a bit of a strange result (only passing through 3.5v instead of 5v (can be seen from ~0.34s))
To enable you guys to check it, i've made movie of the results, what do you think?
To make it easier to speak about, order of measuring in video was Blue > Green > Yellow (both on connector and on motor)
[youtube]kB0rWImvquE[/youtube]