Hello everyone,
I recently broke this mosfet trying to find the current draw on fan0 pin on the SKR v1. 4 board, how I achieved this I don’t know, but that is my talent.
My trouble shooting was that the fan on fan0 run at 100% and can’t be controlled, the heated bed goes to 100C and can’t be controlled and when I touched the Q2 mosfet it burnt my finger. I think I’m on the right track, is there anything else I should be checking and where would I get this misfit because I’m having trouble finding it online.
Thank you in advance
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Hi Thor,
I’ve found the datasheet for that MOSFET here:
Core don’t stock any N-Channel MOSFETs that are that beefy, if you get the specs from the datasheet though I’m sure you can find an equivalent in the same TO-263-2L package from a distributor like RS Components, Element 14, Mouser or Digikey.
I’m not too familiar with those control boards so I’m not sure what usually fails to get a thermal runaway like that happening. Perhaps someone else more familiar with the SKR boards has some ideas on what usually fails.
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Hi Thor
Are you sure this is “broken”. Quite often this centre pin is connected to the large metal back of the device which is soldered to a big chunk of copper track to assist in heat dissipation. This is then the same connection as the centre pin which is cut off or just not there.
Cheers Bob
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Thank you for the replies,
I had a second board that also stopped working for a different reason, so I thought I would swap the mosfets. When I was doing that I found this little doo-ma-hockey was discoloured so I scratched it with my nail and the resine broke off, so I’m thinking this may be the issue as its connected to the fan I couldn’t control.
I think I’ll try swapping that as well.
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Hi Trent,
Sorry for the rely slow reply. I finaly had 10 minutes to sit down and test it and cooked it good and proper. O have sorted open the main fan and heat in the open possion, so Ive cut my losses and got a MKS GEN L 2.1 and external mosfets.
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Hi All
Add on to my previous post:
If this Mosfet has failed short circuit and is switching inductive loads (Fan???) my experience with Golf buggies tells me that the flywheel diode across the fan will almost certainly be open circuit. While this may not destroy the mosfet immediately it won’t take long. With the golf buggy switching a reasonably hefty motor and indeed with any inductive load it is good practise to replace this diode when replacing a failed mosfet even if it tests OK with a multimeter.
A point to note: This diode may be disguised as another mosfet sometimes of the same type using the body diode with the gate and source connected together. I haver seen this on several occasions.
Cheers Bob
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Hi Thor,
Sorry to hear that, I hope you have more success with the MKS GEN L 2.1 board.
Testing circuit components in-situ on a PCB is very difficult and virtually impossible without proper documentation and a schematic to tell you what values you should be measuring.
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