UM2 print head fans not working

[gluetolf 5]

Today I discovered, that the print head fans of my UM2 didn't run anymore. I had a look at the wires and discovered, that one came loose at the end where the cables from the electronic board are. I tried to fix it while the printer was running on a long run, but I had the two wires crossed for a short time. First the fans did run, but after that they just stopped. Please help, I need to get my print head fans back. What should I do to recover from this short? Thank you, Gregor

 

[illuminarti 18]

Reversing the polarity to the fans shouldn't hurt anything, but they will only run with the correct polarity. However, if you shorted out the pins between the board and the fans - got a spark from them most likely - there's a chance that the something broke on the electronics board. (I know that if the LEDs get shorted, the dimmer circuitry can blow and get stuck with the fans 'half on' - I presume the same can happen for the fans).

So first check all the wires again, and make sure all the connections are good. Turn the fans on full, and see if they run. Try kickstarting them by hand to see if they are getting tool little power). Try and measure the voltage at the board pins (should be 24V), and also check the wiring at the printhead.

 

[gluetolf 5]

Maybe I soldered the wires the wrong way around. I will check that, but I already have one electronics board that seems broken here. Same problem with the fans before, still no replacement sent to me.

 

[gluetolf 5]

Now I measured all with a multimeter and the problem I got is, that I don't see the serial setting of the two fans. I got 20-24V on the measurement at the ends, where I only want to have 12V. I also had a look at the um2 assembly manual and will check the wireing with that.

 

[gr5 2,172]

The fans are wired in serial. The wiring that breaks the most is just above or inside the print head. You can slide up the black netting (you might have to cut off some heat shrink) and inside you can see the 3 fan cables (black/red cables). Two of them are connected together with a short loop to make the fans serial.

You want 24V across both fans with 12V across each. If you are getting 24V across one fan and <1V across the other then the fan with 24V across it is "open" or has a bad/broken wire or connection.

You can turn the fans on without printing anything by "starting" a print but immediately go to TUNE menu and play with fan control there. As long as you stay inside TUNE menu the printer will not start printing.

 

[gluetolf 5]

Ok I got that, now I try to restore it how it was... maybe later this week. I have a print job running that I don't want to stop in the middle. Yes, the wires broke coming from the electronic board. As my printer is from one of the first batches, I didn't have to cut off anything One short green cable is connecting the two fans, on the one there's the green cable coming from the electronic board (= green cables), and on the other there's one green and one yellow cable.