Sunhokey Prusa i3 hotend/extruder won't stay hot

I bought the Sunhokey Prusa i3 Acrylic printer last month as my first printer. It is the third in our household as my husband has been printing for 4 years. I assembled the printer in one day and got things printing right away. The install was easy and with the help of my husband I managed to get everything wired up as the directions were missing for that part.

After a couple weeks of printing I began to have issues with the extruder staying at temperature. Then it started not heating up to the target temp at all - which means the print won't start. Power cycling everything will sometimes get it running again. The last time I ran a print the heat just dropped off at hour 3 like I turned the hot end off. I don't know what to do at this point. I have changed the wires from the power adapter to the board as the one that came with the system seemed to be heating up to the point that they burned my fingers. I changed out the thermistor for the extra one that came with the kit because the connector on the board was extremely loose when plugged in. That cleared things up for about 5 hours ... then again back to the no joy.

I have the printer on now with both the hotend and the heatbed on and I'm watching the temp fluctuate on the hotend by a range of 15 degrees while not actually in use.

Do I go through the hassle of ripping out the board and replacing it as well as the extruder/hotend?

I'm going to assume the wiring isn't the problem. Maybe the mosfet for the hotend has gone bad. Try setting the pin number of the controlled cooling fan as hotend and use the fan connector for the hotend. If that works it's very likely the mosfet is bad. If you've got some soldering skills you can replace it with a heavy duty logic level one like IRLB8743. I use that one and it doesn't even feel warm to the touch. If soldering is not your thing you can try replacing the board.

Edited 1 time(s). Last edit at 10/27/2015 04:34AM by imqqmi.