MAXTEMP strikes again

After a month long string of ordering parts, replacing components, changing firmware, troubleshooting and eventually fixing, my rogue MAXTEMP issue is back! To say this is maddening is understating…

after printing maybe 20-25 of this one particular model I suddenly started getting MAXTEMP shutdowns and noticed that the heat graph was spiking ±20° ish. It usually would only spike up that high but occasionally spike low 10° or so. The bed thermistor readings were also noisy. I then started replacing components in order of likelyhood.

  1. Replaced thermistor, still happened
  2. Checked wiring harness for continuity, checked out fine
  3. reverted to old firmware and resliced model, still happened
  4. Replaced original Mini1 RAMBO with Mini2 V1.3 RAMBO, Still happened
  5. Replaced power supply, fixed issue

I have no idea what could have happened to the power supply that it would have caused it to become so noisy that the RAMBO couldn’t filter out voltage spikes. But after replacing it, the noise on both the bed and hotend thermistor readings cleared up enough to print another 25 or so models before coming back.

This is a screenshot of the heat graph on the second consecutive MAXTEMP shutdown.
heat graph

What in the world is causing this? Why was I able to print 10x 1 hour prints yesterday and have no issue then suddenly it starts freaking out again? Could it be the heater cartridge going bad and slowly killing my power supply? It is the only thing I haven’t replaced yet, I just dont get it…

I took the hotend up to temp and let it sit there while I wrote this and here is the heat graph:
It looks acceptable to me, then again I am used to this temp wobble. I have never had a nice flat line since I have been monitoring temps with octoprint like I have seen from other printers. (I have done a 230° autotune)

I looked for replacement heater cartridges for the hexagon hotend and the 2 usual sources came up dry. At this point I am ready to just replace the entire toolhead. Any insights or thoughts will be greatly appreciated.