Help with fluctuating hot end temperature

dvdsnyd 2021-11-07 04:36:37 UTC #1

Hi all, been a long time! Glad to see this community is still somewhat active :-). Hoping to get some help.
I've been battling unsteady/fluctuating hot end temperatures for a while.
I honestly can't recall exactly when it started at this point.
I have a stock MKS gen 1.4 board, running 24 V.
I am using a genuine e3d titan with V6 hotend.

I get temperature swings of 10 degrees and sometimes more. To the point that it sometimes takes a while for a print to actually start.
I've adjusted the hysteresis temp to try to battle this, but it's gotten to a point that it something I want to fix.
Things I've just looked into.
Replaced the thermistor - same style as before. Totally replaced wiring. No Change
Ran PID tune after PID tune - no change
Replaced the heater cartridge and heater block, No change
Ran PID tune after PID tune - no change
Checked board connections - all look good. Used crimp ferrules when upgrading to 24V

I'm at my wits end. I don't know what more to do. Not even sure where to begin to look.
Thanks for all your help!
Dave

dvdsnyd 2021-11-07 05:39:49 UTC #2

A quick update
I noticed that around 100C the temperature was solid, so I wanted to further test this. so I ran it at multiple intervals:
set point - 100C - Rock solid
set point - 150C - Rock solid
Set point - 200C - Solid, +/- 1C
Set Point - 225C - OK, +/- 4 c
Set point - 245C - Getting worse - +/- 6C
Set Point - 250C - out of control - +/- 8-10C

What would cause behavior like this?

Tin_Falcon 2021-11-08 00:19:01 UTC #3

did you replace the thermistor
i asume a 24 v heater

dvdsnyd 2021-11-08 20:04:25 UTC #4

Yes, that's one of the first things I did. Yes 24V 40 W heater

csorrows 2021-11-09 01:25:00 UTC #5

Are you sure it's not using bang bang mode? If no change from PID tuning, this might be the problem.

dvdsnyd 2021-11-11 22:46:33 UTC #6

@csorrows
PIDTEMP is defined

dvdsnyd 2021-11-13 16:04:02 UTC #7

I ended up disabling PIDTEMP and went to bang bang...not idea, but it is holding much more consistent at the 250 temp than before. I got my new MKS Gen 1.4 board, so I'll try that sometime this weekend hopefully.