I am running ramps 1.4 and marlin 1.1.6 with an E3D hot end. Where should I start looking if my printer is having problems maintaining temp? As in occasionally the temp drops as much as 20 degrees before the heater can catch up. I am planning on running a new auto tune once the current print is finished. As near as I can tell my temp sensor is good and the heater cartridge measures what it is supposed to.
fix the thermister on hotend it would be loose if it doesnt fix the issue do the auto pid calibration
always autotune with the part cooling fan on . alternatively use insulation on your heater block to protect it from the blowing fan.
Perhaps a loose wire or intermittant connection if you haven’t checked for that yet.
i had same problem, the termistor cable is loose at the termistor end. it was not well tinned
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@Jeremy_Wasserstrass There are a couple things that you can easily check before you do the PID autotune that should all be pretty quick!
-Make sure the thermistor is securely held in the hotend.
-Make sure all the electrical connections are tight along the hotend and heater.
-Turning on and off a fan, whether it be the hotend fan or even a room fan can cause sharp changes in temperature if the printer isn’t calibrated to handle it.
I had this problem also. First I had problems with the heated bed.
So I installed a stronger mosfet module which fixed the problems.
Now I have the same problem with the hotend. I orderd at alirobbery another kind of mosfet breakout but I am still in a little fight with it. It starts to work emidately when I power the Ramps up without any temp instructions and keeps on going until the Ramps goes into panic and I disconnect the power.
But overall, it seems to me that the mosfets wear down overtime and start to give problems. I also noticed the latest Ramps release has a cooling fin attached to the mosfets.
Hi @CatweazleMagic! This is content that was imported to Maker Forums from Google+ when Google shut down Google+ (thus the gplus label), and the user you are trying to converse with has not yet logged into Maker Forums, so they won’t get notification of your question, sadly. 
MOSFETs can fail open, and yes overheating can make that more likely. It’s common for MOSFET breakout boards to have heat sinks for that reason.