Replicator 2 Extruder Fan Won't Run (not a fan failure)

[DHeadrick]

My friend has a Replicator 2 which has been printing for 5000 hours.  Here is the history behind it:

- Last year sometime, he accidentally shorted the connectors for the LED light strip on the front edge of the case.
- After this, he noticed that the extruder fan (on the front of the cooling block) would run constantly (not just when the nozzle temp was over 50C)
- Just recently, this fan has stopped working entirely (the fan will run when supplied directly with 24V from an external source)

I'm not very familiar with the guts of the electronics board under the Replicator 2... is there a way to fix this?

he seems to think that the MOSFET can be replaced?  Is this true?  If it can be done, I can do it (I've successfully soldered on circuit boards of laptops before).  I just won't bother trying if that is not the cause of the issue.

Can anyone enlighten me on the magic that is within the Mightyboard?

[tramalot]

yes probably the MOSFET, it can be done but a hot air wand is preferable as there is quite a large area to heat (the heat sync section)

[Ryan Carlyle]

Probably the fan FET. Running always-on is a dead give-away. They're a bit delicate on the Rep2 and R2x... Not like the RevE boards that use a ~20A FET to run a 0.07A fan.

[DHeadrick]

Is it possible to replace it with a more robust FET?  Is there anyway to find out the specs on the existing one so I can locate another on Digikey?

[Jetguy]

https://groups.google.com/d/msg/makerbot-users/nSI3gdb2TCo/la0bEK_S8GQJ\

I've circled the MOSFETs in question in red. Specifically, Q11 and Q9 control the extruder fans, Q7 controls the main blower duct on a Rep-2

I found the specifics here:

Dan Newman posted in the Tips and Tricks group in reference to a user with a 2X obviously a Rev G or H board https://groups.google.com/d/msg/3dprintertipstricksreviews/Vgq2z2_x1zc/9PfZqflsbBIJ

"The MOSFET they use for the cooling fan is a 2N7002K which is good for 60V but 
only 0.3 A. So make sure that the two fans combined use do not exceed that 
current rating @ 24V.

Due to the size of the picture, it might show up hidden under "quoted" here in google groups so be sure to expand to see it.

[Jetguy]

This thread we kind of kicked around exactly what you are asking, is there a better FET that could work. I don't know (I don't own a Replicator 2 series) so it's untested, but we had some pointers to try out.
https://groups.google.com/d/msg/makerbot-users/_arqq2V-TQ4/KOwzkcwvBwAJ

Again, keep in mind the 24V source and read all the posts in that thread, there was a fair amount of back and forth and good input.

[Gian Pablo]

Yeah, the replacement dmn3033 in SOT23-3 package worked fine. I'm using it to drive bigger fans.

[DHeadrick]

After reading the threads linked (thank you BTW!), I have decided to try the DMN3033 with a fall back of moving Q11 to Q9 (since the Rep2 doesn't use Q11 because of the lack of dual extruder).

[DHeadrick]

Also (in case anyone knows of any gotchas), I've confirmed that the board in question is Rev G.