Help with fluctuating hot end temperature

[dvdsnyd]

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]

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]

Replaced the heater cartridge and heater block, No change

did you replace the thermistor
i asume a 24 v heater

[dvdsnyd]

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

[csorrows]

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

[dvdsnyd]

@csorrows
PIDTEMP is defined

[dvdsnyd]

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.

[dvdsnyd]

Guys,
I am absolutely lost on this one...
I installed my new MKS Gen 1.4 board, same behavior.
The thermistor is new - no splices or connectors except the one at the board
The entire hot end cartridge is very new, new heater core and block
I've run PID Tuning for hours. I've tried hand tuning. There is something else going on as far as I can tell.
I've tried using bang-bang, I thought it was better, but it isn't after running it more. Actually eerily similar.

The thermistor I'm running on the hot end is the standard 300C offering from e3d and slice

I get about 12-15deg slow up and down variation on the hot end. It is fairly cyclic in nature.
When turning on the printer, the ambient temperature of both hot end and bed thermistors reads some fluctuations, about 4 degC. 16C to 20C, I'm in the corner of my basement. Temp is cool, but constant.
I've upgraded from 12 to 24 V. I have a meanwell 24V PSU.
To try and eliminate the PSU, I installed my bench top power supply in place of the current one.
I tried ant both 12V and 24V. I get weird fluctuations at no load, ambient temp.
It will go wonky for about 60-120 seconds with 4 deg fluctuations, to running within about a deg for another 60-120 seconds. This is on both the bed and hot end.
I have searched and searched, and cannot for the life of me find anyone else that has had a similar problem.
The common answer to temp fluctuations seems to be PID tune, which has not helped.
Any ideas?
I'm at my wits end.
Dave