I've never liked the placement of the motherboard cooling fan on the Rep1. It pulls air from the heated build chamber and randomly blows it into the motherboard chamber. There have been some great mods here on Thingiverse to solve this problem, but after looking at most of them, I wanted a simpler, less invasive way to better cool the motherboard.
Once I turned the printer over and looked at the situation, I quickly saw that if you just relocated the fan to the edge of the cover board it would pull air from the open area underneath the printer where it is much cooler and the fan would blow air more directly onto the motherboard. And best of all, there is minimal drilling involved, and no messing with the motherboard.
My fan was starting to go out, so I recently upgraded to an Orion fan (Digi-Key #1053-1208-ND) It's incredibly quiet and runs at 7cfm, a tad higher than the stock 6cfm (hey, every bit helps..). I actually replaced my extruder fans with the 6cfm version of these babies as well. I hardly know the machine is on now - highly recommend swapping these out. But if you don't want to buy new fans, the stock fan can be moved and used with this mod as well since it's the exact size as the Orion fan.
4 - #4-40x.75 machine bolt
4 - #4-40 nut
4 - #4 washers
4 - #4 split-ring lock washers
4 - 5/32 rubber washers (optional - there isn't much vibration induced noise generated by these fans..)
First, print the bracket on your printer. I printed it at 100% infill, 1 shell, .2 layer height.
Turn off, and unplug your printer.
Turn in onto the left side. Unscrew the bolt holding the motherboard cover plate to expose the board and fan.
Unbolt the fan and remove. You shouldn't need to unhook the wiring to the fan during this operation, though it might make some of the steps a little easier.
Mark the location of the fan bracket on the cover plate and drill 2 mounting holes. See photos, but I mounted mine next to the opening in the cover so it would blow air both onto the board and down the side of it into the cavity.
Mount the fan to the bracket as shown in the included pictures. Be sure and pay attention to air flow direction of the fan. It should blow towards the label side of the fan. You want the fan, once mounted, to blow into the motherboard cavity. You can use the rubber washers if you like to dampen any vibrations, but they are probably not needed. These fans run very smoothly. I didn't notice any difference if I used them or not.
Mount the fan/bracket assembly onto the cover plate and re-install the plate.
I created the bracket in Autodesk 123D. I've included that file and saved it as a DXF file - not sure if this will be usable.
Note: The bracket in the photos is a version 1 prototype. I removed the inner fillet (don't know why that was there), and decreased the space between the mounting holes for the cover side to reduce interference with the fan mounting bolts.