Hi all,
after I changed the heatbed of my K8200 I got wrong temp reading from the heatbed thermistor.
I checked the resistor and capacitor on the input, but they seem ok.
The thermistor is directly connected without any protection to one of the ADC inputs of the 2560.
These inputs are easy to damage if you work on it with static electricity (ESD).
I tried the pin next to it on the 2560 to change the input pin to the pin next to it wich was not in use in the Marlin sketch but
this pin defining must probably set in more places so I stoped with this after a few tries.
I don’t want to give that much money for a new board wich has only a damaged ADC
So I replaced the Atmega 2560, put in the bootloader and firmware and it works with succes
this only cost me €5 instead a new board 
I read this wrong temperature reading problem more here on the forum so if you have a damaged ADC input just put a new 2560 on the controllerboard.
You can do it by yourself if you have good soldering skills.
I hope this is helpfull
greetz
Floris