Spiky hotend and bed temps 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.