Self test error  

Re: Self test error

Yes, that has been an issue in the past. Cables stressing because of movement and breaking internally.

Usually it is just at the back of the extruder where the cables turn 90 degrees into the bundle. It is possible to splice, but replacement is usually quicker (especially with the fans).

Peter

Re: Self test error

Thanks, Peter!

Any insight into how the above error messages are generated?

And has someone worked out a better (more durable) way to attach the cables to the extruder? I don't want to have to do this again every few months.

I'm thinking about using a high quality multi-core cable to traverse the extruder, then splice the cables in loctions exposed to less stress.

Re: Self test error

I found that the z-axis only moves up, not down, when I use Settings>move axis> z-axis.

When I move the cables going into the extruder, I can make the z-motors move the z-axis down.

The z-axis motors are not connected to the extruder cable bundle, so I think some cables are shorting against other cables, or ground, in the extruder.

i bought an assortment of multi-core cables today, a metre each, to try out what might work to fix this problem once and for all.

Re: Self test error

When I run the Calibration> Self test, then the left side fan is spinnig, the front fan is not spinning. I have disconnected the front fan and found that the red cable does not have continuity, it appears to have broken internally. I did not notice this because most of my recent prints were high temperature prints with the part cooling fan off.

When I click "Spinning" at the 'Front print fan?' stage of the self test, then Checking Endstops commences and then ends with this error message:

Selftest error!
Please check :
Endstops
Wiring error Z

When I reset the printer and then go to Settings>move axis, then X moves normally in both directions, Y moves normally in both directions, the extruder spins (if nozzle is preheated), but the Y-axis only moves up, not down.

It affects both y-axis motors equally. Sometimes the Y-axis moves down, but I cannot reproduce it.

At the start of the last large print that completed, the side (heat-sink) fan was running erratically. It was turning off periodically, I thought it was related to the position of the cables entering the extruder, because most of the time, when moving the wiring harness, the fan would come on again. This problem stopped by itself and the print completed fine.

I have disassembled the extruder and unwrapped the cables between RAMBO and extruder. They look OK, and everything supplied by these cables seems to be working fine.
Any ideas for how to troubleshoot this issue?

Thanks for any help with this, Mik

Re: Self test error

When turned on, the position of the Z axis at that time determines the Z=0 position which the printer will not allow moves below, so the Z axis will only move up at that point. It should however then be possible to move back down to the assumed "Home".

Have you tried the Auto Home option in the LCD menu? If you do, be prepared to reset the printer is the nozzle touches the bed (make sure the extruder heater is off).

Peter

Re: Self test error

Thanks, Peter.

I was aware of the need to move the Z-axis up, before it will move down, but I had not tried the Auto-home function.

I selected Auto-home (in submenue Calibration) and everything is back to normal. As normal as you can expect when the printer is dis-assembled as shown below. What I mean is: The axes all move, the self test progresses as it should (when I lie about the front fan function) and the Z-axis starts to move downward at the right time in the process. I have no doubt it would complete the self test if it was assembled. The broken red cable to the front fan of course is still broken and the fan does not spin.

I did nothing else before the "Auto home" command, no wiggling of cables.

Now I have moved the cables randomly for a bit, and the Z-axis will not move downward any longer.

I repeated the "Auto home" command, and this time it ratles around X- and Y axis, and then stops when the downward movement of the Z-axis should commence.

At least I know now that the "Auto home" does not fix this intermittent problem. My biggest worry was that I'd put it all together again, just to get hit again at random by this baffling malfunction.

Next thought: Maybe a cable is only almost broken, therefore it's resistance is too high for the stepper motor current, and the thin part of the cable heats up when being used, then the resistance rises further until there is insufficient current for the Z-axis stepper motors. On one occasion earlier today I thought that the downward movement of the Z-axis was slower and incomplete after each upward move (via turning the knob).

If this hypothesis is right, then the Z-axis should work for a little while when the printer is 'cold' after rest, like when I tried the 'auto home for the first time. And, it should continue to work much longer in 'silent' mode. I changed from long-term 'silent' mode use to 'high power' mode use during the last 25hr print that completed. It may well have something to do with it. I'm not certain, but there may not have been any Z-hops during the last 42mm Z-height of the 200mm Z-height print. That could explain why it completed: No downward Z-axis movement was required.

Next idea:
If the failure of downward Z-axis movement is due to extruder cable problems, then it might be resolved if I unplug the extruder motor cable connector from the RAMBO. I tried that, the Z-axis does not move down, but up. Unfortunately it proves nothing, because if for some reason one of the 4 cables to the Extruder needs to be intact, then unplugging it should cause the same problem.

If anyone could try this out for me on a working i3 MK2, that would answer my question:
If you unplug the 'Extruder Motor Connector' on the RAMBO, can you then still control the Z-axis motors and make them move down?

Thanks for any help with this, Mik

Re: Self test error

Could it have something to do with the 'always on' state of the Z-axis motors when the power is on?

Re: Self test error

Checking if any of the other cables entering the extruder might be causing the Z-axis 'no-downward-move-malfunction':

Unplugging in succession without plugging them back in:

PINDA probe connector: No downward Z movement.
Y-axis motor connector: No change
X-axis motor connector: No change
Z-axis motor connectors: Stops the upward motion of one Z-motor as well as the downward motion, but no downward motion occurs. When one or the other Z-axis motor connectors are disconnected, then there is a high pitched whining noise. If both are disconnected, then I do not hear a noise.

Z-endstop removed: No change
Y-endstop removed: No change

Re: Self test error

I think this is a defect on the RAMBO board.

Here is why I think so:

Connecting either one of the Z-axis motors to the Y-axis output, they both move in both directions. That rules out cable damage to Z-motors.

Connecting the Y-axis motor to one of the Z-axis outputs, it only moves in one direction.

Is this particular RAMBo specific to the Prusa i3 MK2, or can I buy a different RAMBo locally to save time?

Re: Self test error

When the probe cable is broken, the Z end stop will be set to "true" - you can view the end stop current readings in the LCD.

So if the end stop is on, then you will only be able to move upwards. Problem is that the end stop will remain on. Check the LED on top of the probe. It is on when the end stop is not triggered.

I think you will find cable damage on the probe as well as the fan.

Peter

Re: Self test error

I sent a link to this post and brief description to the "Contact Support" button on the Prusa website.

http://help.prusa3d.com/contact-us?contact_query=Please%20enter%20your%20question

I had been sending email before, but got no replies, I'm not sure which email is supposed to be used for this.

Is it [email protected] ?

Re: Self test error

When the probe cable is broken, the Z end stop will be set to "true" - you can view the end stop current readings in the LCD.

So if the end stop is on, then you will only be able to move upwards. Problem is that the end stop will remain on. Check the LED on top of the probe. It is on when the end stop is not triggered.

I think you will find cable damage on the probe as well as the fan.

Peter

That makes sense!

And you are right, I found the problem and can now repeat it:

When the printer is on, the red light on top of the PINDA probe should be on. It only turns off when it senses proximity to the calibration points in the print bed. When I wiggle the PINDA probe cable, the light comes on and off, and the downward movement of the Z-axis is always disabled when the light is off, and enabled when the light is on.

Now if I could only figure out if the break is in the probe or the cable. It's infuriating how I can not pin down the exact location of the intermittent disruption.

I already ordered a new PINDA probe on Dec 10th.

Re: Self test error

The break in the cable will be where I have sai on many occasions (not necessarily in this thread though)...

Right at the back of the extruder where the cables bend 90 degrees to enter the cable bundle. It's the point where the long vertical cable tie is placed to hold the cables against the back of the extruder body.

Peter

Re: Self test error

Thanks again, Peter! 🙂

I think my last print broke the cables, it was moving for practically the full X-axis range to 160mm z-height at 0.25mm / layer.
The cables were bent to their extreme positions 160 x 4 = 640 times.

I will probably print several more such prints, so I need to fix it well.

I have bought some extra-flexible cable, meant for stage use. The 4 cores inside it have 40 strands of coper each, I think I'll use that in one way or another, it might resist repeated bending better than other cables.

Re: Self test error

I think I have 'nailed it'! 😆

Lot's of soldering and multiple layers of shrink-wrap tubing to hold the shortened filament and cut-off steel nail together.

Practically all movement of the cables at the critical 90deg kink is thus prevented.

Re: Self test error

Only time (printing time that is) will tell for certain if this works to prevent the extruder cables breaking on Prusa i3 MK2.