New front fan won't stop (Replicator2)

[brian conlan]

Hey gang,

Y'know that fan on the Replicator2 that sits in front of the heat sink on the extruder assembly? The 40mmx40mmx10mm square one. 

I just replaced the stock Makerbot fan with one of these:

http://www.amazon.com/40mm-10mm-Case-Cooling-Bearing/dp/B00AMQ5M8C/ref=sr_1_1?s=pc&ie=UTF8&qid=1449153376&sr=1-1&keywords=40mm+X+10mm+New+Case+Fan+24v+5CFM+PC+CPU+Cooling+Ball+Bearing+2+Pin

It's lovely– quiet, smooth, efficient. Problem is, it won't ever shut off as long as the printer is on. The old one would stop spinning once the temp dropped below 50ºc and would not be spinning when nothing was actively printing. The new one runs ALL the time. You'll notice that the new fan is a simple 2-wire jobber running into a 3-wire connector. To make it work, I simply cut the connector off and spliced the old Maker bot one on. Black to black, red to red. 

The second photo shows the new wires going into the original slots on the mightyboard. I am 99% sure that I put the new wires in precisely where/how the old wires came out.

Any ideas? 

THANKS

[Dan Newman]

The FET controlling the fan has blown on your motherboard. Pretty common actually;
plenty of people have had them die on their Rev G and H motherboards. It's easy
enough to replace if you're okay soldering.

Dan

[brian conlan]

Excellent! I'll google that repair and hit you back if I can't figure something out. 

Thanks for the quick reply!

[Jetguy]

Here is an older thread. Note, some of the pictures are hidden- click on the "quoted" portion to reveal them https://groups.google.com/d/msg/makerbot-users/N1A4wGJLOOo/hzmMimikq_8J

On Thursday, December 3, 2015 at 10:27:03 AM UTC-5, dnewman wrote:

[brian conlan]

Perfect- I'll get a pile of those FETs while I'm at it. (Surely this won't be the last one I blow)

[Dan Newman]

On 03/12/2015 7:41 AM, brian conlan wrote:
> Perfect- I'll get a pile of those FETs while I'm at it. (Surely this won't
> be the last one I blow)

I believe there's only three on the board: two extruders and one print cooling fan.
They don't deal well with fan failures, shorts (however brief), or back current (e.g.,
suddenly stopped/siezed fan). They mostly got the rev G and H boards right except
for those three FETs (saving pennies again?), switching over to custom wiring
harnesses and connectors (makes it harder for customers to service/repair their
bots), and omitting half the endstop connectors (definitely saving pennies; the
maxim of omitting unused components to reduce failures is a bit of a stretch in
this instance).

Dan

[Gian Pablo]

If you are going to replace the FETS, you might as well go with a lower voltage but higher current part.

I ended up going with a part rated for 30V but 6A. This is the part # on Digikey: DMN3033LSNDICT-ND MOSFET N-CH 30V 6A SC59-3

I am using higher output fans on my Rep 2X and they would not work with the existing FET.

[brian conlan]

@Gian That's a good idea. Got any observations about print quality / consistency changes with higher output fans?

[Gian Pablo]

The major change was in high resolution (100 micron) and dual extrusion prints.

High resolution means that filament is flowing through more slowly, and dual extrusion means that the filament is sitting in a hot extruder for a while. Both of these factors contribute to thermal creep, to the filament softening at the point that it enters the extruder nozzle (thermal barrier to be precise). This causes jams.

The higher output fans helped a lot with this. 

The challenge is that the high output fans are TOO strong, and can interfere with the extruder getting to temperature. For a while I ran the fans from a bench power supply, so I could vary the voltage, but with the new FETS I am thinking of setting up a simple voltage divider and trimpot.