Weird problem with extruder temperature

So I'm running marlin 2.0.5.3 on a prusa steel and for a couple of weeks I've been having this issue. It's best described with the video below. I changed the thermistor I tuned the pid but I don't think it's a software issue. Help
[youtu.be]
The problem starts at about the 1 minute mark. The printer prints fine up until the thing with the temperature starts acting up. The temperature is read fine by marlin as I tested it with a thermocouple. The problem is not constant. Some times it does it, some times not.

If you watch the temp you notice it jumps up and down a bit.

The final jump is from 231 to 263!

I suspect a damaged ADC on the controller. perhaps a non functioning missing bit.

In your firmware enable #define SHOW_TEMP_ADC_VALUES and AUTO_REPORT_TEMPERATURES
Start up a terminal package at correct baud rate and send M155 S1 (report temperature and ADC values every second)

If you use pronterface you need to enable Settings|Debug Communication to see the temperatures

the log will look something like (this eg im not heating up.. just a cold room)
SENT: M105
RECV: ok T:8.31 /0.00 (1000.69) @:0
RECV: T:8.25 /0.00 (1000.75) @:0
RECV: T:8.06 /0.00 (1000.94) @:0
RECV: T:8.25 /0.00 (1000.75) @:0
SENT: M105
RECV: ok T:8.19 /0.00 (1000.81) @:0
RECV: T:8.25 /0.00 (1000.75) @:0
RECV: T:8.44 /0.00 (1000.56) @:0
RECV: T:8.25 /0.00 (1000.75) @:0
SENT: M105
RECV: ok T:8.25 /0.00 (1000.75) @:0
RECV: T:8.13 /0.00 (1000.88) @:0
RECV: T:8.25 /0.00 (1000.75) @:0

(pronterface is also sending M105's every 5 seconds...)

The number in the brackets is the raw ADC value (i suspect averaged, as it should only have 0-1023 values. no floats)

Log heating up to 232 like before. and post the results...

Edited 1 time(s). Last edit at 06/20/2020 05:57AM by Dust.