printer won't start

My printer will not start printing, It is 2 years old and it will heat and get close to temp on hot end then good down a few degs then back up, sometimes if I turn off and back on it will start, other times it will warm up for an hour then start printing. It is a stand alone printer and I run prints off a sd card. Any help would be greatly appreciated, thanks Doug

Hi, I had a similar thing happen which was caused by a bad crimp connection to the solid wire that comes out of the heater cartridge. You have to slide the insulation back to inspect the connection. If it's loose at all you will probably see some discolouration where it's getting hot. If an intermittent connection is the problem it's easy to recrimp it with side cutters or pliers, or a crimp tool if you have one. If that's not it, you could try a PID tune to see if it helps. Fairly well down the list of possibilities is a bad mosfet or an intermittent connection between the microcontroller and the mosfet.

I have tried to run the pid autotune and all it does is hover around the 200 range, goes down to 198 then back up to 202. I will check the wires, the wire that goes to the front of the heater has a dark spot but not the heater cartridge wire. Is the autotune suppose to go up and down in temp? thank you so much for your help

I haven't run an autotune in a long time, but yes it's supposed to do as many cycles as you tell it to in the command. From the wiki

Quote

M303 E0 S200 C8
This will heat the first nozzle (E0), and cycle around the target temperature 8 times (C8) at the given temperature (S200) and return values for P I and D.