Hello,
There are not long my extruder fans stopped working during printing. I saw that the cables were cut so I resoldered them and checked with a multimeter that there is no short circuit. And when I restart the fans do not turn, I tried the fans with a power supply they all work well. Little strange thing, when I measure the current leaving the terminal blocks of the fans I have about 12 volts whan the fans are not connected and when the fans are connected it’s about 2 volts …
If anyone has had this problem or know how to fix thank you to tell me how to do 
English isn’t my native language so I hope you understand all, please ask me for any questions
Are you sure you didn’t reverse the wiring (+ on -).
Check one fan at a time to check if there’s a faulty one.
The voltage should be between 6 and 12V when the fans are running (depends on the speed).
no my cables are not reverse…
How come the cables here cut in the first place?
Hello did you find a fix for this?
My cabels was short circuit from the beigginng, and now I have the same problem after sorting out the cabels on the 50mm fan (big one) Her is a picture, the cabels wear in my meaning stripped too long and got in contact when spinned
Dear guys,
normally a shortage like this would damage the switching transistor for the fans in a short time. Since Vellemann uses 12V fans but is operating with 15V supply voltage, they have to prevent an overload on the fans. For this reason they implemented a shunt resistor, where the overvoltage should be compensated. This resistor is located at the left side of the heater PCB towards the backside of the printer. This resistor becomes hot during normal operation.
In case of a shortage of the fans the whole supply voltage drops across this resistor. I measured a value of 11.2 Ohm, so in case of a fan shortage an electrical power of 20W is generated, the resistor design is for 0.5W max. power. So it will die as a heater.
Finally there are many options how the resistor will behave later on: it can be completely open or it can have a significantly higher resistance value. For the latter case you will still measure the correct voltage without the load of (correct) fans. But you cannot provide the necessary power for the fans.
My proposal: check the resistance of the fan resistor, maybe it will be necessary to change them.
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