Looks like I fried my RAMPS 1.4 mosfet.

(Mark Estefanos) #1

Looks like I fried my RAMPS 1.4 mosfet. Anyone know a good alternative I can get from frys or radioshack? Are there any other stores that stock them? I want to get printing sooner than later.

(Chuck McManis) #2

Well Digikey (http://www.digikey.com) and Mouser (http://www.mouser.com) do have next day service. You are probably not going to find one locally unless you live in China. If you want to get it from Fry’s you will need to find the NTE equivalent and see if they carry it (doubtful). I don’t know what city you are currently in so local places are hard to specify.

(Mark Estefanos) #3

Thanks for the help! I’m in Huntington Beach, Orange County. Any ideas? I’ll get IRLB8743PBF online otherwise.

(Chuck McManis) #4

I don’t know of places but these guys would: http://larobotics.org/

(Mark Estefanos) #5

Do you know how I can check whether its the polyfuse or the mosfet that’s gone bad? My heat bed tries but fails to get to temp and eventually refuses to heat up at all once the RAMPS is hot.

(Chuck McManis) #6

Polyfuses are self healing fuses, either its open (blown) or shorted (not blown). It transitions from one state to the other fairly quickly. A multimeter measuring the resistance across the terminals should show close to zero ohms.

Harder to test the MOSFET in circuit but presumably a lot of RAMPS owners out there have debugged this board a number of times so you should be able to get solid answers on the RepRap forums.

(Mark Estefanos) #7

Thanks! I’ll check the resistance.

(Evan Nguyen) #8

If you are in a bind I can loan you a Ramps board until you get yours replaced. I’m in Irvine

(ThantiK) #9

@Chuck_McManis , polyfuses, once tripped also become easier and easier to trip.

(Chuck McManis) #10

That is very true. It would be a shame if the RAMPS 1.4 circuit was constantly tripping the fuse though. It would suggest a more serious design issue.

(dstevens lv) #11

Marvac is close to you. I don’t know if they stock them. I just searched them online and came up empty. For the FET you can use either http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/FDP8870/?qs=TIe0t8ne476%2bdM5I4duLTA== or http://www.mouser.com/ProductDetail/International-Rectifier/IRLB8743PBF/?qs=%2Fha2pyFadui97xXKZV5A71C7%2Fq2rBisybdlZdVP85R4%3D

The issues with RAMPs and the FETs and fuses has been discussed plenty at the Reprap forum. http://forums.reprap.org/read.php?219,169361,169595#msg-169595 It’s not so much a design issue as it is application issue. I’ve used them in high duty cycle environments with good results.

(Mark Estefanos) #12

So I’ve got almost 0 ohms of resistance on the polyfuses. I’ll check the amperage going through next.@Evan_Nguyen Thanks for the offer! I may take you up on that once I can narrow down the issue. @dstevens_lv Thanks for the information, I’ll look into it more.

(Mark Estefanos) #13

Welp I screwed up. Tried to measure amperage across one of the polyfuses and the board ended up sparking and killing my PSU. I think the RAMPS is fine since it can run off of USB still, but I have no idea. I’m assuming I wasn’t supposed to do that.