I have my UM2 (2.1.4 control board) on a work bench in my garage/shop area. During the summer the ambient temp around the printer is in the low 90sF - no air conditioning in the garage. I have been having print failures during long prints at these high ambient temps. On one occasion, I observed the Z axis drive stepper motor drive the build plate down by about 1 inch between layers, resulting in "printing in air". This is the type of random failures that I have had. This led me to look for overheating on the control board and I found the same indications of high temp on the circuit board (around the driver chips) as others have reported - a light brown color around the chips for the X, Y, and Z axis ICs. Since I wanted to continue my printing projects and contacting UM for a solution would mean a delay, I chose to add a cooling fan to the board enclosure and heat sinks to each of the driver ICs. I ordered the heats sinks, thermal conductive adhesive tape, and a cooling fan from DigiKey.
Here are the parts that I ordered, part #s are Digikey:
Heat sinks (X5)- P/N AE10837-ND, 10mmX10mm, $0.78ea (smallest of this type that they had)
Thermal tape - P/N 1168-2057-ND, 12mmX1120mmX0.25mm, $2.09ea
Cooling blower (X1, powered from the 24V fan connector) - P/N 1570-1036-ND, 50mmX20mm, 24vdc, $8.79ea
I added heat sinks to all 5 driver ICs even though the E1 extruder IC areas was only mildly discolored and the E2 device isn't used...yet. The heat sinks are inexpensive and are easy to install. The E2 driver is for the 2nd nozzle upgrade if we ever get one. I cut out some of the louvers in the short side of the control board cover to improve the blower air discharge flow and mounted it using a longer bolt in one of the cover bolts holes. I can't help you with a part number or source for a plug for the 24V fan connector, I cut down a strip of pin plugs I had left over from a pinball machine repair. The blower does add to the noise level of the printer and it does run all the time but at 29 dba, it isn't very loud and I don't really notice it. I could add a switch but then, where to mount it (another project)? I also printed four "feet" for the printer to improve air circulation under it. For other part sources, the Digikey online catalog has references to the part OEM and their p/n.
Yes, I know all this is probably overkill, adding just the blower to stir the air under the printer may have been sufficient. But if a little cooling is good, isn't more cooling better?
I've been printing for about 3 weeks now, including 4 prints that required 10 to 12hours each (ambient air temp 85F to 95F) and have not had any more problems, so I consider this project a success. In my opinion, if your board is getting dark, I would look into adding some additional cooling. I understand that UM believes that the darkening is of the solder mask and is acceptable, if not normal. My limited experience indicates to me that the thermal design is marginal on the driver ICs (based on my Z axis control channel issues on long runs in high ambient conditions that seem to clear up after cooling down, along with these indication of high temps on circuit board), but it could be an isolated device issue as well.