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I have been using my MK3 for about a year with no problems, but a couple of weeks ago I started to have the following issue: the printing head loses its first layer height calibration, apparently for no reason. Sometimes it goes higher and the plastic line gets loose from the plate and sometimes it goes down, scratching the plate.

I already calibrated the first layer several times, it works for a while and then goes bad again. Today I calibrated the first layer twice, proceeded the PINDA calibration as well, flashed the new release, and nothing: my MK3 is no longer printing right. There must be a faulty part, possibly the PINDA sensor or something else. Once the first layer is done, the rest of the piece goes right, that is why I suspect that the PINDA sensor is failing.

Could you please, give me any clue on how to overcome the problem? Also, could you list the possible faulty parts so I can order them?

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    $\begingroup$ Maybe too obvious :-) , but I have to ask, have you checked the hotend carriage and probe mount if there is nothing loose or broken? $\endgroup$ – 0scar Jul 26 '19 at 11:52
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    $\begingroup$ Along the lines of what @0scar has stated, have you checked to ensure your z-axis rods are tight? I'm talking about where the rod attaches to the motors. If they aren't holding correctly, it could be giving you fits in both directions (up or down). $\endgroup$ – Pᴀᴜʟsᴛᴇʀ2 Jul 26 '19 at 13:54
  • $\begingroup$ I had a similar problem with a MIGBOT. There is a tube that feeds the filament into the hotend heater/nozzle/thermistor block, the tube is held in place with a setscrew in the hotend block. Turns out the setscrew had backed out enough for the hotend block to wobble around. Took things apart, retightened the screw, re-assembled, re-leveled, no problems since. $\endgroup$ – CrossRoads Jul 29 '19 at 16:25
  • $\begingroup$ Thanks for the comments! $\endgroup$ – Marco Vettori Jul 30 '19 at 18:07
  • $\begingroup$ Indeed, I checked those items and everything is firm in place. The problem seems to be the PINDA sensor: I performed the test recommended by Prusa and found some disperse readings, what must be causing the error in height of the nozzle in the first layer. It might be consequence of the new FW, where the initialization leveling now is faster, maybe causing unprecise readings. $\endgroup$ – Marco Vettori Jul 30 '19 at 18:12

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