I recently rebuilt my A8 printer to have a metal frame and replaced the board with a GT2560 reva+. I'm having problems with the temp readings from both my hotend and hotbed. Using marlin 1.1x and Its possible I have something configured incorrectly. I can get successful prints with good quality but sometimes I get thermal runaway during a print.
Both cold and at temp (200c) have fairly large temp spikes. I didn't have this problem with my old board. I had much smoother temp curves. I'm using the default PID values for Ultimaker Kp 22.2, Ki 1.08, Kd 144.
I have tried to use PID autotune but get drastically different values every time I run it and using the results gave worse results (sometimes giving a heating error during the autotune). I checked all the wiring and nothing looks frayed or damaged.
First pic is cold temps. Second is trying to do a PID tune. Third and fourth are during a print.
I had a similar problem and there could be three reasons(if the connections are ok):
- thin wires to the hotend
- one of the MOSFETs was fried
- the termal sensor wasn't good enough insert into the hotend
Try to measure the hotend heating element voltage while printing.