I’ll do a few more tests in a bit.
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I messed with all my screens yesterday and even a bunch that I flashed for orders. None had any error message when homing, and the headless one shows no errors or any sign of M420 in the terminal window when homing.
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Two somehow different Marlin installs that should be the same, and us in the middle… LOL
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Guys, bad news: someone else (a new LR3 maker) has now hit the error of “Unknown command: M420”! Link below. I linked them over to this thread so they could read about the ongoing efforts to solve the issue.
I told them,
Ugh. This is now the second time today I’ve read about someone hitting an error of “Unknown command: M420”! Please check out the discussion beginning at the link below, and continuing onward. (Hint: they are still working on it!)
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I have no idea what the heck that can be. I have updated 6 old screens and 50+ new ones, and I have not seen it once.
I hate not knowing what the heck.
Same here. No clue how it can happen to one group of people and not to the other.
There is an easy fix for it. This fix - to my mind - is minimum-invasive, but you need to amend and compile the source code of the tft screen for it:
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There is a function in ‘usr/API/parseACK.c’ which suppresses specific messages coming from Marlin, i.e. these messages - although posted by Marlin - will not be shown on the tft screen
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This function uses the array ‘knownEcho’ to specify which messages should be ignored. Now, if you add the M420 command to this array in line 39 it will be safely ignored:
{ECHO_NOTIFY_NONE, “Unknown command: "M420”}, // M420
Interestingly, there are a couple of other entries in this array already dealing with the the M420 command …
This fix works perfectly for me and is not dependant on what BTT / Marlin do with it. It should also work for the Repeat users. So, if this M420 message - for whatever reason - is thrown by Marlin, it will be suppressed. And if it is not thrown, well, then it won’t be shown anyway. The downside is that you will never see this message again on your tft, even if it is thrown by Marlin for a good reason. But I decided to live with this risk.
Alternatively, you can revert the change BTT introduced in Feb (see above). But because I don’t understand Marlin well enough I thought my second option would be better.
I updated my MP3DP Screen and my Primo screen and now both say “No Printer Attached” they were working just fine before the update…
This is a different issue. It is probably the baud rate set incorrectly.
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Ok i will start a new thread. thank you!
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I am not super interested in maintaining edits that are that deep. If we can figure out why two of you are seeing this issue, that I can submit it to BTT and get the repo fixed. Always best to get the issue fixed that try to maintain a band aid.
Wondering if more will pop up. Both of you have had other firmware flashed to your screens and BTT does make firmware that is non-down gradable at times. Last time we wanted to go back it caused the screens to show upside down on previously good firmware and could only be fixed with new firmware.
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Agreed!
Wondering if more will pop up.
I don’t hope so!
Both of you have had other firmware flashed to your screens
Are you sure? I haven’t followed the other thread, but the screen Doug / Sway pasted in looks like the stock firmware to me.
If we can figure out why two of you are seeing this issue
More than happy to support this analysis.
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Okay, I went to submit a bug report and someone had already done so this morning. Fingers crossed this is a quick fix.
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Okay, PR is in the works, Fix "Unknown Command: M420" bug by kisslorand · Pull Request #2752 · bigtreetech/BIGTREETECH-TouchScreenFirmware · GitHub
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Did they verify it was legal in their state, or did they have a note from their doctor? That’s usually the issue with (M)420 problems…
I’m in California, that is why I was so concerned. It should not be an issue here. 
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Have just applied the fix to my sources and it works. No (M)420 problem anymore 
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Awesome. He said he was the cause of the issue so I am glad he knew how to fix it.
I like his attitude. Maybe we can get some CNC specifics over the line in the future.
Me too, I was thinking about that earlier. He has helped fix a lot of issues on those screens.
Hello, I just did the update and I have the same problem as Christian Avatario, when I do a homing in the tactile mode I am getting the error ‘unknown commander:“ M420 ”’ (when I do it in Marlin mode the message does not appear).
I have realized that of all .bin files that contains “CNC TFT package.zip” the one that has used (it has renamed .CUR) has been BIGTREE_GD_TFT35_V3.0.27.x when my TFT is a BIGTREE TFT35-E3 V3.0.1
Shouldn’t it has used the BIGTREE _GD_TFT35_V3.0_E3.27.x.bin or the BIGTREE _GD_TFT35_V3.0_E3.27.x.bin? (I do not know the difference between whether or not GD)
Thank you and I’m sorry but my English is very bad and I use the Google translator.
Hola, acabo de hacer la actualización y tengo el mismo problema que Christian Avatario, cuando hago un home en el modo táctil me da un error ‘Unknown command: “M420”’ (cuando lo hago en modo Marlin no aparece el mensaje).
Me he dado cuenta de que de todos los archivos .bin que contiene “CNC TFT Package.zip” el que ha usado (ha renombrado a .CUR) ha sido BIGTREE_GD_TFT35_V3.0.27.x cuando mi TFT es una BIGTREE TFT35-E3 V3.0.1.
¿No debería haber usado el BIGTREE_GD_TFT35_V3.0_E3.27.x.bin o el BIGTREE_GD_TFT35_V3.0_E3.27.x.bin? (No se la diferencia entre que sea o no GD).
Gracias y lo siento pero mi inglés es muy malo y uso el traductor de Google.