Temp Error/Temp Offset Migrate between Boards via Marlin firmware builds??

My understanding was that each new Marlin firmware .bin build and flash (especially with M502+M500) flushes out any previous errors or conditions, but I had a MAXTEMP E1 error reboot/reset loop migrate from one SKR 1.4 to a new one even though I checked all hardware, thermistors, and used clean, rewritten Marlin files. I'm wondering if Marlin/ PlatformIO reuses or migrates error conditions from dependencies or otherwise even using fresh/clean Marlin files?

Complete story here:
I got a weird problem (a handful of related problem reported on Reddit) I've been trying to figure out for the week. My SKR 1.4 Turbo (correctly) posted THERMAL RUNAWAY/thermal errors several times, I had a frayed heater wire, eventually it wouldnt restart, stuck in reset MAXTEMP E1 loop.

I replaced heater rod and thermistor, tested resistance good, and I tried everything with firmware I could think to get it to boot past error, no go, so I got a new board SKR 1.4. USBed it to Pronterface, worked fine, then wired it up to printer, the MAXTEMP error came up again, I unplugged all hardware, reflashed it with clean Marlin, the only way I could get it to boot was to first #define dummy 25C 998 temp, showed 300C in PFace, so I defined MAX TEMP to 300C, then in Pronterface it posted that temp unmoving.

Tried multiple edits to any relevant firmware settings, pins files, M502 factory resets, SD card format, tested known working thermister, and could not get TH0 or TH1 (P0_23, P024) plugs to work, or anything other than 300C reported for HE temp. I'm assuming 300C is open circuit/max/same as no thermistor? I just tried clean installing VS Code, deleting all the dependencies, IDEs, And yes, I'm checking that each new firmware is indeed overwriting last, has the right time and date, and several attempts using clean Marlin files. I stopped short of messing with any temperature.h or thermistor.h files, those are outside my understanding.

My only guess is that somehow the error or bad temp calibration/offset got effectively hardcoded on the board, migrated somehow from last board to new one, via firmware?--Is that possible? Do you have any suggestions? I've been on the Marlin Discord spamming those poor guys for the last week trying to figure this out, theyve been super helpful, but so far no fix.

The only other remote possibility is that this brand new board arrived with a non-working TH1 and TH0 port (HB P0_25 TB works fine) OR the MKS MINI 12864 display board or its SD saves errors and migrates them.

Latest attempted fix involved uninstalling VB Code, PlatformIO no luck--might have to try VMWare virtual machine to eliminate any other sources.Thanks

Edited 3 time(s). Last edit at 05/22/2020 02:31AM by okolepuka.

"I'm assuming 300C is open circuit/max/same as no thermistor? "

No this is a short circuit. NTC Thermistor resistance decreases as temperature increases.

Unplugged thermistor is max resistance and min temperature...

Edited 1 time(s). Last edit at 05/22/2020 02:28AM by Dust.

Most of what your purpose is just not how it works at all. Error conditions a not saved by anything. Not in eeprom, not in code. Not in the compiler.

Most likely scenario is the shell of your heater heater cartridge became live with 12 or 24v this made the heater block live the first time the machine was turned on.
Also one of your thermistor leg was touching the heater block. This sent 12/24v to the chip and instantly killed the pin.

Many a crappy heater cartridge from china comes like this... check the resistance from each wire to the shell. there shouldn't be any continuity

Check the resistance from each pin of the thermistor wire to the the alu heater block. there shouldn't be any continuity

Either that or the thirmistor legs are shorted in the heater block... which will also kill the pin i'm told.

Sine the fault was not successful corrected, the second board suffered the same fate as the first.

Gotcha--yet again, Dust to the rescue--I'm assuming this is Dust from the Discord. Thanks man

An addendum, I just got a New (3rd) SKR 1.4 Turbo in the mail today. I carefully checked it to be working first, then when I plugged everything in the the CPU fizzled and smoked, bricked immediately.

I've built multiple computers, basic Arduinos, Hackintoshes, wired my van with homemade lifepo4 batteries and solar panel system, 20 years of varied electronics, mechanical and soldering experience, I thought 3d printing would be an easy stretch--this hobby is kicking my ass and bleeding my bank account.