LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
I have an MK3 which is exhibiting several issues intermittently. Last night I tried my first non-trivial print, and there was a layer shifting on it that corrupted the print. The issues that I am seeing are:
LCD display corruption - Sometimes what is displayed on the LCD is not correct. I have seen this only during calibration. This photo shows an example, you can see the LCD says "2 of 4G" instead of just "2 of 4":
https://mhumphrey.smugmug.com/PrusaMK3/i-rLFnL8v
Lock-ups, sometimes with garbled LCD, sometimes with blank LCD - During first layer calibration last night, the machine stopped and the LCD was completely garbled. It also locked up once during Z-axis calibration, but in that case the display was blank. Here is a picture of the garbled LCD:
https://mhumphrey.smugmug.com/PrusaMK3/i-pr57xgT
Layer Shifting - Here is a picture of the print I was trying last night:
https://mhumphrey.smugmug.com/PrusaMK3/i-gGDFFHv
The print was from this design: https://www.thingiverse.com/thing:119689
LCD backlight flickers when unit is powered off and bed is manually moved along Y-axis - You can see this in the video at this link:
I know that stepper motors will generate back-EMF when moved, but typically one would design the circuitry to prevent this from escaping to other parts of the circuitry (I am an Electrical Engineer). So I was surprised to see this, and am wondering if there is some issue with the electronics. I have double-checked connections to the Einsy, and made sure everything was reseated. The LCD corruption problems seem intermittent, and I have been able to do several smaller prints with no major issues.
Any ideas what might be the issue?
Re: LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
I can only help with your last point (LCD backlight flickers when unit is powered off and bed is manually moved along Y-axis) and can re-assure you its normal.
When you move the bed, the motor turns and it acts as a generator sending powers "into" the printer and this illuminates the screen, so its not related to your other problems.
Jon
Re: LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
About your last point: it is completely normal and if you move Y fast you might even destroy your stepper drivers or electronics.
Sometimes my MK3 also shows a wrong char on the display - I could not care less.
Re: LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
3. Do you have your printer in Stealth mode? Or do you have crash detection turned off? That's a MASSIVE layer shift, and I can't imagine what would cause that, besides a nice crash.
1 & 2. These are similarly related I think. I would jiggle the connectors at both ends of both LCD wires, and verify they are not "pinched" anywhere. I hate ribbon wires.
4. Seriously, don't push it fast. You can kill your drivers, and with the built-in drivers on the mk3, that means a new Einsy board. Not cheap. (unless you are really really really really good with a soldering iron, then you could just swap the chip) This is normal on every 3D printer I own.
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Re: LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
Thanks everyone for the responses. I am aware of how stepper motors can generate back-EMF when moved (I actually mentioned this in my post). I guess what I was not expecting was that this is allowed to spill over into other parts of the circuitry where it may cause damage. It's 100% preventable with good circuit design. BUT, since it seems to be normal on this printer, let's put that aside.
I saw a couple of posts saying the "LCD corruption" was normal. I could see the occasional wrong character due to the long ribbon cable. However, I don't think this explains the picture I posted with the entire LCD display corrupted and the lock-ups that I mentioned. Is that considered normal too?
Re: LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
3. Do you have your printer in Stealth mode? Or do you have crash detection turned off? That's a MASSIVE layer shift, and I can't imagine what would cause that, besides a nice crash.
I am not running in Stealth mode. I will have to check on the crash detection when I get home. I have not changed any of the defaults - printer is configured as it came from Prusa.
1 & 2. These are similarly related I think. I would jiggle the connectors at both ends of both LCD wires, and verify they are not "pinched" anywhere. I hate ribbon wires.
I have already done that.
Re: LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
About your last point: it is completely normal and if you move Y fast you might even destroy your stepper drivers or electronics.
Sometimes my MK3 also shows a wrong char on the display - I could not care less.
Yes, but does it scramble the whole display and then lock up? I wouldn't think that is normal behavior.
Re: LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
Layer Shifting - Here is a picture of the print I was trying last night:
https://mhumphrey.smugmug.com/PrusaMK3/i-gGDFFHv
The print was from this design: https://www.thingiverse.com/thing:119689
Layer shifting is often caused by loose screws used to lock the pulley to the stepper motor shaft. Those screws can sometimes work their way loose, so even if you're dead certain they were tight before, I'd check them again.
Re: LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
I just checked, and crash detection is ON.
Re: LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
Layer shifting is often caused by loose screws used to lock the pulley to the stepper motor shaft. Those screws can sometimes work their way loose, so even if you're dead certain they were tight before, I'd check them again.
Thank you. I just double-checked that. Nothing seemed loose, but I did tighten the Y-axis pulley grub screws just a little bit.
Re: LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
Thank you. I just double-checked that. Nothing seemed loose, but I did tighten the Y-axis pulley grub screws just a little bit.
If it was possible to tighten them at all, then they were probably loose.
Re: LCD backlight flickering when bed moved and power is off, LCD corruption, layer shifting
Last night I went through the printer from top to bottom. The first thing I noticed was a huge blob of PLA stuck on the underside of the extruder. THis was just the perfect size to not be visible until I tipped the printer over. I suspect this is related to the layer shifting that happened during my print. I went back over every screw and made sure it was tight, and rechecked belt tension (which was fine).
A couple of other findings:
The LCD board is not grounded very well, and is very sensitive to static discharge. This is what is causing the display corruption. Also, the connectors on the end of the ribbon cable are some of the worst connectors I have ever seen. They are brand new and yet very loose. All this combines to make the LCD display very susceptible to losing its state. I did the best I could w/o replacing those connectors (which I will do at some point), fishing more cable through and making sure that there is no strain on the LCD connectors. I also place another zip-tie in a place that should help anchor the ribbon cable better.
I think maybe my z-axis first-layer offset was too low, so maybe things were coming unstuck. I've bumped it up a little (it's currently -0.625). I was able to do a small print last night with no issues, and the quality looks OK. I'll retry my larger print tonight.