Maybe the easiest thing to do is to test another stepper motor. I think that even a high-quality stepper from OMC can break down.

good luck and good success 👍 

So I can only conclude the stepper is failing.  Any other options?  Only fails when completely cold, and by that I mean the stepper because I am not heating the bed.  If I run tests too close together it does not fail.  I have to let sit idle for >30 minutes to reproduce.  I'll swap in the old stepper to confirm.  Not clear what failure mode would produce these results.  This is a decent quality stepper from OMC-stepperonline which worked perfectly for over a year.

@dan-rogers

I’ve done all that except for unplugging and replugging all on driver board.  I guess I’ll try that.  I wish PR flipped the board around and put the door to the outside.  It is so confined and painful to work on the way it is.  But I’ll give it a go and report back.  BTW I replaced the y stepper over a year ago so it’s actually the newest one on the printer.  

I wasn't happy with the original Einsy case either and for that reason looked around for something else and found, printed and installed this (including Raspi).

https://www.thingiverse.com/thing:3239428

@karl-herbert

do you mean swap motors or swap connections to einsy?  

First of all, I would replace the plug contacts to rule out any mechanical axis components. If the problem then occurs with the X-axis, there may be a problem with the stepper or driver.

I’ve done all that except for unplugging and replugging all on driver board.  I guess I’ll try that.  I wish PR flipped the board around and put the door to the outside.  It is so confined and painful to work on the way it is.  But I’ll give it a go and report back.  BTW I replaced the y stepper over a year ago so it’s actually the newest one on the printer.  

do you mean swap motors or swap connections to einsy?  

Every 25 hours, check the bed and bearings and belt tension for needing adjustment.

Every 5 hours clean the gunk/varnish off of your print head.

Every 100 hours, check to see your pulleys have not loosened.

It's like a boat.  Maintenance schedule will keep you humming.

I have an original mk3 that’s been printing fine for years.  I just got through a project printing 3+ kg in last two weeks flawlessly.  In last couple days I’ve had a few intermittent cases where the bed fails to move to home before mbl.   Then it crashes against endstop when leveling moves far enough.  Once I get the mbl cleared I can print without issue.  It has not failed during a print, only when first starting up after sitting idle for a bit, and only a few times. 

The first couple times it happened I heard a strange groaning/chattering sound and saw the bed slowly moving back.  It sounded like either too little current for the load or running too fast and skipping steps.  But I have made no hardware or firmware changes in a long while.   After those couple loud moves, the failure mode since is more silent where it doesn’t move at all or only makes partial move and just stops.  The bed moves very smoothly by hand so I don’t suspect bearing failure (I’ve upgraded and repacked in past).   I ran belt test and other tests and all pass.  

Is it possible the tmc driver could be starting to fail, or maybe passive component on board?   Again, only seems to occur intermittently from cold start.  The actual mbl moves seem fine, it is just the initial axis home that fails.  Printing is fine.  Not sure next step to debug. 

Have you ever checked the y-axis pulley screws? If the printer is somewhat older, an electrical plug contact on the einsy board may be corroded or there may be a loose contact in a wire somewhere. Does the error also occur when you replace the Y-stepper with the X-stepper?

The first couple times it happened I heard a strange groaning/chattering sound and saw the bed slowly moving back.  It sounded like either too little current for the load or running too fast and skipping steps.  But I have made no hardware or firmware changes in a long while.   After those couple loud moves, the failure mode since is more silent where it doesn’t move at all or only makes partial move and just stops.  The bed moves very smoothly by hand so I don’t suspect bearing failure (I’ve upgraded and repacked in past).   I ran belt test and other tests and all pass.  

Is it possible the tmc driver could be starting to fail, or maybe passive component on board?   Again, only seems to occur intermittently from cold start.  The actual mbl moves seem fine, it is just the initial axis home that fails.  Printing is fine.  Not sure next step to debug.