Limit switch error during print

[Ahiggs 1]

Hello,

 

We have an Ultimaker 3 that is currently being a pain. In the past few months we have printed without issues. Now, it is often displaying the axis is stuck or limit switch is broken error during the middle of a print. It has happened for both the X/Y axis and the Z-axis for numerous different sliced models (Cura 4.4).

 

When the error occurs, the printer stops moving, extrudes a small blob of filament on the print and then shows the error and fails. I have never actually seen what happens before the failure, but it typically occurs during the first few layers of the print

 

I have cleaned and oiled the sliding rods for the extruder. The printer moves smoothly and passes the X-Y motion stress test. The print quality is fine when it manages to print successfully...

 

Any advice?

 

Thank you

[gr5 2,176]

I've been around on this forum quite a bit and unfortunately I don't know much about this error.  It seems to be somewhat rare maybe?

 

Could you please say which error number it is?  Is it 17?  From reading this it sounds like the error only happens during homing?  Anyway it suggests a few things to check.  Although I'm wondering if you are getting a very similar, but different error?

 

https://support.ultimaker.com/hc/en-us/articles/360011573780-The-X-or-Y-axis-is-stuck-or-the-limit-switch-is-broken-ER17

 

Errors 16 and 33 also sound similar.  I guess step 1 is to figure out which error number you are getting.

 

Also regarding Z errors - look in the back of the printer under the print bed (just pull the bed up).  Under the bed is a long screw that sticks down.  Directly below that is a hole.  Clean out that hole.

[Ahiggs 1]

Thanks for the quick reply. I will need to check again when it fails, but I am 95% it was 17 once and I think another number a different time. Once the message was for the X-Y axis and once for the Z axis.

 

There are no issues with the limit switches that I have seen. It always homes correctly. I checked the z-switch hole and it was clean. 

 

Also, during the most recent print, I managed to walk by the printer before the error occurred. It seemed like something happened during the first layer causing the head to stop moving. The fans were running, but the lights on the print cores were off (not visible in picture). The motors were idle. It almost seems like the printer lost communication to the motors and extruder but thought they were still connected and continued to print. 

 

I have updated the printer firmware to the latest version, but Cura is still on 4.4.0

[Ahiggs 1]

I just received error 18 (communication with print head) when unloading the material from print core 1.

I first unloaded material 2 which went without issue. I then tried to unload material 1 which went fine until the head started to move back to home when it was done unloading. The motors just stopped and the error appeared before the head was even close to the limit switch.

[gr5 2,176]

This is very strange stuff.  Never heard of any of this before.  There's 3 boards under the printer.  One is for the display.  The other 2 each have a computer.  The smaller red one, made by Olimex, has a powerful cell-phone like computer on it running linux.  The white one has an arduino type computer on it and runs the steppers (and more).  They communicate through some kind of serial interface (I think USB).  I think there is literally a USB cable that connects them together.

 

I'd check that cable - unplug it and plug it back in.  On both ends.  But... lights going out?  I think the white board powers the red board so I don't see how it could lose power without the red board losing power and the display also going dark.  The display is controlled from the red board (not 100% certain but pretty sure).

 

The quickest (and most expensive) option is to just replace both of those circuit boards.  I'd ask your reseller how much that would cost.  If you only replace one, the white one seems more likely to be the problem (from your description).

[gr5 2,176]

Another thought.

 

There are 2 bowden tubes and an electric cable going into the print head.  On UM3 printers it's a common problem that the electric cable works it's way loose.  There are 4 long (very long) screws at the top of the print head.  Remove the rear 2 and the head will still hold together but let you remove the panel towards the back on top of the head.  Push down on the connector - make sure it's seated all the way and put it all back together.  Giving the cabling inside a little bit of slack.  Some people put a shim around the cable so it can't slide up and down.  Maybe some tape or some paper.  Or just don't worry about it unless it happens again.

[Ahiggs 1]

Hello, sorry about the delay in response.

 

I have watched exactly what happens when the error occurs. During printing, maybe on the 4th or 5th layer, the extruder will stop moving, feeder motor will stop (I think, didn't hear grinding noises), both print core lights will turn off, but the printer will think that it is still printing. If I select abort print, it will sit there motionless and then display the Z or X/Y limit switch error, presumable because it thinks the extruder/bed is moving and never detects the limit.

 

I checked the cables underneath the printer and everything seemed fully seated. I will check the print head cable tomorrow, haven't done that yet. It's possible that this is loose since I have had to open the head before to clean out a clog.

 

Thank you!

[gr5 2,176]

Okay - you are losing 24V.  24V is used only for a few things:

steppers

heaters (bed and nozzles)

some lights maybe

some fans maybe

 

The computers and display don't need the 24V.

 

Like I said above, there is a white PCB under your printer.  That is the failing board.

 

One solution is to get a replacement.  You can contact your reseller.  If you are within warranty they should send it for free.

 

Or you can fix it yourself.  There is a relay on that board, K1.  That relay is your problem.  The relay isn't needed.  You can just short it out so that 24V skips over the relay.  I have a post and a video about this somewhere - let me look...

 

So that's for a UM2 but the UM3 has a very similar board.  The position of K1 might have changed.  I'll go look for the UM3 white PCB schematic now.  If I find it I will make another posting below.

 

 

[gr5 2,176]

Here is a pdf of the schematic - K1 is on 3rd page upper center (area 4B).  Just below K1 you can see where the 24V comes in "Supply connection".  

 

Anyway if you do the exact same jump as I did in the photo above it should fix your issue.  Assuming the problem is with K1.

 

I'm realizing as I look at the schematic again that this jump means 24V is always going to the stepper drivers even with power off but I guess it doesn't matter as I've been using this printer since 2014 and it still works great.

 

This link takes you to both the schematic and the pcb layers - the copper layers and the text layers and the solder mask layers.  No changes were made between UM2 and UM3 in this area of the board.   zero.  None.  I can definitely see some key differences (UM3 has filament detection connectors?  what?).  K1 is typically a white box right near where the 24V comes in.

 

https://github.com/Ultimaker/Ultimaker3/tree/master/PCB files/1548-I Ultimainboard/Schematics and layout pdf

[Torgeir 243]

Hi Folks,

 

This relay only serve as a power switch for the 24 VDC.

As gr5 said, it might be used for external fire/smoke detectors for disabling power to the heaters.

 

Sorry for the noise.

Torgeir

 

 

 

I'll say this approach might be a risky thing to do by solving the problem "permanently" this way, cause this relay actually is a safety device, -hence cutting power to heat bed and heat block if one of the temp sensors fails..

 

This relay is a high priority element in our UM2 printers that "turn off" the high current to items (all heaters and stepper motors) inside the printer.

 

Just to be mentioned.

Thanks

Torgeir

 

Edited March 18, 2021 by Torgeir
Not correct!

[gr5 2,176]

I know, right?  but not true.  That circuit doesn't do anything.  There are two connectors "safety 1" and "safety 2" also known as J16 and J17.  On the UM2 there are jumpers in there that jumper the 2 pins together bringing 5V through both connectors to the chip U7. 

 

The idea is you can put a connector there and run it off to some safety equipment - maybe a fire alarm.  But it's not really documented and no one has ever done it (most likely).  In the UM3 they even removed the connectors and the circuitry!  But left K1.

 

[gr5 2,176]

Here you can see the latest UM3 PCB.  Red circled area is where the safety1 and safety2 connectors used to be.  Green circled area is U7.  I have other photos from earlier days when UM3 *did* have connectors there and jumpers.

 

 

Now signal PA6 from the arduino also arrives there but I think that is only to monitor the signal - not to flip K1 open.  Because otherwise it would have to overdrive U7 and I don't think the arduino (actually atmega - whatever) has the power to overdrive U7.  I didn't look up the specs.

 

Yes - now U7 is gone but there are probably thousands of UM3's out there with U7 still installed.  Probably over 10,000.

 

So overriding K1 should be okay.  I'm kind of surprised it doesn't blow up the stepper drivers but whatever.  It doesn't.

 

I guess it *is* slightly dangerous that you have 24V going to parts of that PCB even when power is switched "off".

 

I've had my UM2 in that situation for years.   It's off more than on but always connected to the 24V power supply.

 

[gr5 2,176]

@Ahiggs - actually, if your UM3 is older - your whole issue might be those 2 jumpers.  I circled them in red in the photo above!

 

They may be a little loose - when things heat up (after an hour of printing) things expand and one of those 2 jumpers might cause an open which shuts down your 24V power!

 

Try sliding them out and back in.  They are black.  They are in the area circled in the photo above.  You only have to remove I think 4 screws to get at those.  You don't need to remove the board or flip it over - just get access to those 2 black things there.

[gr5 2,176]

@Ahiggs - here's what I mean - the two black connectors - one is pointed by the red arrow here - the other is just below (hidden by that white cable):

 

 

This website explains how to remove the cover (it's pretty obvious!)

https://fbrc8.zendesk.com/hc/en-us/articles/115005017923-Electronics-Board-UM3-UM3X-

 

 

[Ahiggs 1]

Alright, so I reseated the white cable in the print head. It did not look loose or under tension but I was able to print a 11 hour part immediately afterwards, so maybe this was our issue. If we continue to have issues, I'll take a look at the relay.

 

Thanks for your help!