Ready for repairs

[gnydick]

My soldering skills and equipment have been growing. I've got many boards with fried MOSFETs from short circuited fans. I'd like to try to repair them. I've had reasonable success repairing SMDs the size of a grain of rice with just a regular iron and proper technique. Is it possible to repair the duet 2 with just an iron?

[dc42]

@gnydick it's easier to remove the 3-pin mosfets with just a soldering iron if you also have low melting point solder such as Chipquik.

[gnydick]

@dc42 thanks. Can you shoot me a part number?

[droftarts]

@gnydick for Duet 2 parts, see https://docs.duet3d.com/en/User_manual/Troubleshooting/Parts#replacement-parts

Ian

[gnydick]

@droftarts thank you!!

[gnydick]

@dc42 forgot to ask. I have so many boards and I haven't inventoried them, I don't remember which MOSFETs are blown. Is there a passive (no power supply needed) way to test the health of them?

[dc42]

@gnydick said in Ready for repairs:

@dc42 forgot to ask. I have so many boards and I haven't inventoried them, I don't remember which MOSFETs are blown. Is there a passive (no power supply needed) way to test the health of them?

If the mosfet has a hole blown in it, it needs to be replaced. Your multimeter should show a diode between the source and drain terminals, and no short circuits between any terminals.

[gnydick]

@dc42 awesome, thank you for the education.

[droftarts]

@gnydick do you feel like getting added to the list of community repairers here? https://forum.duet3d.com/post/127089

Ian

[gnydick]

@droftarts maybe after I actually do some

[gnydick]

@dc42 I tested all 3 fan mosfets and they are fine, and the 1A fuse is not blown, but I have a couple of fans that don't work anymore. Is there anything else that I can check on the board?

[dc42]

@gnydick you can command the fan on and off and measure the voltage between the mosfet gate and source. It should be 0V when the fan is commanded off and on the Duet 2, 3.3V when it is commanded on.

Also check the mosfet for signs of damage. If the mosfet has gone open circuit then there may be a tell-take mark on it.

[gnydick]

@dc42 thanks. I don't have any way to hold/move probes accurately and precisely enough without touching other components. How do you do it?

[dc42]

@gnydick search for needle tipped multimeter probes.

[gnydick]

@dc42 I have tremors, is there anything like "helping hands" that aren't just crappy alligator clips on stiff bendy arms that aren't very precise or accurate?

[gnydick]

Also, I have a system with a fan that won't turn off, I'm guessing that's a bad MOSFET?