Z-calibration fails & PINDA is always 1  

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Rob
 rob
(@rob)
Active Member

Dear all,

I have been using my Prusa MK3 for quite some time now until yesterday... the printer would not start a new print.

I have been trying to re-calibrate, but I encounter an error in the Z-calibration: It goes up normally, then it would not go down and says that the calibration is failed and I have to "check the axes."

I read both the handbook and some answers in the forum but I could not figure out a solution. Can someone please help? I suspect the problem might be the PINDA Probe since the value of the sensor is always 1.

How can I fix this?

Best,
Rob

P.s. Here is a video of the situation.

This topic was modified 1 year ago by Rob
Posted : 09/05/2019 10:18 am
Rob
 rob
(@rob)
Active Member

Anyone? Please I need help! 😭

Posted : 10/05/2019 7:51 am
Tim
(@tim-m30)
Illustrious Member

Is the red LED on the PINDA on or off.

If on, move a screw driver past the tip to see if it will turn off. If it turns off, then back on when you remove the screwdriver, the PINDA is probably okay.

If always off, and there is no metal near it, then you have a problem with the PINDA or the power to it.  In many cases, it is a broken wire between the extruder and EINSY.  Cables flexing 24/7 will break with long term fatigue.  You can troubleshoot the PINDA and repair broken wires found; or simply replace it. 

Prusa: pinda-probe-testing

It is always wise to get more than one opinion......
Posted : 10/05/2019 8:55 am
Rob
 rob
(@rob)
Active Member

Thank you @tim-m30 for the answer.

LED on the PINDA probe is off. LCD Menu -> Support -> Sensor info says that the PINDA value is 1. It does not change if I put a metal object underneath.

What would you do?

Thanks,
Rob

Posted : 10/05/2019 10:02 am
Vojtěch
(@vojtech-p6)
Honorable Member
Posted by: Rob

Thank you @tim-m30 for the answer.

LED on the PINDA probe is off. LCD Menu -> Support -> Sensor info says that the PINDA value is 1. It does not change if I put a metal object underneath.

What would you do?

Replace the pinda probe. You can buy a new one from Prusa for 17 USD.

Or try to fix the PINDA cable. Most likely either the power (red) or ground (black) wires are broken.

You can either just replace it with any other four conductor signal cable with a Molex SL 4-pin connector at the end or you can find the point where the cable broke and fix just that.

To find the spot, you first need to strip the cable of the round insulation. This can be done by slicing it and pulling. Once the four small cables inside are free, you pull on each one individually, strongly, but carefully. If broken, the copper will not hold the cable together at the point of breakage and you'll see the plastic stretching. Then you cut the cable at that spot, solder it together, shrink-wrap. Now that the cable isn't protected, you can twist it (by removing the individual wires from the connector, twisting by fingers, putting them back). This will protect it from further breakage, as on a twisted cable, the stretching is much less when bending. Then you can put it back on the printer and print happily again.

 

Posted : 10/05/2019 12:18 pm
Rob
 rob
(@rob)
Active Member

Thanks for your answer, @vojtech-p6.

 

I've just removed the plastic sleeve that keeps the cables and played with the PINDA cable. Indeed, that was the problem.

The cable does not look damaged from the outside, but there is something wrong inside in the position highlighted in the image below. Temporarily, I've loosen the cable in this point and the PINDA is working again.

I'll ask Prusa for a replacement part, since the printer is still under warranty.

Best,
Rob

 

Posted : 10/05/2019 1:16 pm
Tim
(@tim-m30)
Illustrious Member

Good you found it.  Seems the PINDA cables are especially sensitive to breakage when handled/flexed a lot.  When you install the new PINDA, be very careful to not sharply bend or stretch or tug on the cable.  

As for where in the cable is is actually broken?  Breaks from fatigue rarely happen at non-flex points.  And that corner isn't one.  The break can be upstream or downstream - most likely in the tail bundle - but flexing that corner just happens to stretch the break open, or push it closed.  

It is always wise to get more than one opinion......
Posted : 10/05/2019 8:07 pm
Vojtěch
(@vojtech-p6)
Honorable Member

The PINDA cable is prone to breaking even at non-flexing sharp bends. The assembly manual warns about it. I believe the reason is the thick, strong protective sleeve on it and the fact that the inner thin cables aren't twisted. When the cable is bent sharply, the sleeve is stronger than the thin copper inside, there is no slack because the copper is straight and the copper tears.

Posted : 10/05/2019 10:17 pm
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