hotend heating when powering on the printer - no temp set

Hi guys,
I recently got a new board (creality 4.2.7) for which I configured and built marlin (the newest available version).
Flash went ok, boot up fine, axes are working, auto-home working, bed heating, probes showing plausible data, all ok - but the hotend is heating full power all the time, without setting a temperature. It will heat up to the firmware-restriction if I don't shut down the printer.
Any idea what kind of silly mistake I have made?
Damn I wish I had tested it with the original firmware...I think it wasn't heating when I started it up shortly, but I'm not sure...

Quote
stahlsau
Any idea what kind of silly mistake I have made?

Yes!

Re-flash the original firmware Else

There could be a short across the Mosfet, this happens quite often on new boards.

The short could be as simple as a solder ball or any thing loose that rolled across and shorting pins.
It could be that the solder of the Mosfet shorted the pins together and simply needs the excess solder removed from its pins.
A quick look could determine it it can be fixed without returning for a warranty replacement.

If you had a multi-meter you could check to see it the output of the mosfet is shorted and a replacement could be installed though this would void any warranty.
It could be a circuit trace that is shorted an needs to repaired...

If it is not a simple fix and you want to continue post!
else return the controller for a warranty replacement.

Edited 3 time(s). Last edit at 11/21/2020 04:50PM by Roberts_Clif.

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Computer Programmer / Electronics Technician

hi,
thanks for your thoughtful answer.
I've reflashed the original firmware and the hotend is not heating (at least not from alone, only when it's told to heat).
So I would rule out a hardware error.

The question is - what could I possible have configured wrong that the heater is on by default? I don't understand that.

I would take a look at your firmware if you were to post a link to the source for original and your updated configurations.
sometimes a 2nd eye can catch possible problems.

By the way I use WinMerge to do my comparing it make the job so easy and download the Zip files..

Edited 1 time(s). Last edit at 11/22/2020 07:50AM by Roberts_Clif.

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Computer Programmer / Electronics Technician

great idea with winmerge. Didn't think of something like that. That prog is a great help.

Well I resetted platform.io and started a new project with vanilla marlin. Then I reconfigured it with the bare needed minimum, et voila!
No more selfheating hotend.
My guess is I configured the wrong pin for the control fan, and somehow this enabled the hotend. Dunno if this is possible though.

Many thanks!