<p>I have a DIY 3D printer with Marlin firmware. I use an LJ12A3-4-Z/BY sensor for the Z probe. Recently I have had a ridiculous problem with Z homing.</p>
<p>In doing <strong>Z homing</strong>, it senses the bed, goes up, and stops, it doesn't go back to the bed...</p>
<p>In doing <strong>Bed leveling</strong>, it goes up without sensing the bed and in the next step goes even higher and higher.</p>
<p>If I ignore bed leveling, it starts printing in the air. If I still use bed leveling, the Z axis moves in long courses in every layer.</p>
<p>It looks like it is saving the wrong Z-axis position as home! These are some related settings that I think of:</p>
<pre><code>#define Z_PROBE_OFFSET_FROM_EXTRUDER 0.25   // Z offset: -below +above  [the nozzle]
</code></pre>
<p>and</p>
<pre><code>// Travel limits (mm) after homing, corresponding to endstop positions.
#define X_MIN_POS -3
#define Y_MIN_POS -3
#define Z_MIN_POS 0
</code></pre>
<p>and</p>
<pre><code>// For M851 give a range for adjusting the Z probe offset
#define Z_PROBE_OFFSET_RANGE_MIN -20
#define Z_PROBE_OFFSET_RANGE_MAX 20
</code></pre>

CC BY-SA 4.0
2021-09-12T20:03:17.527Z
What changed to have this happen? Did you change anything? Have you checked and replaced cables, remounted cables to the printer board?
0scar
CC BY-SA 4.0
2021-09-12T20:26:20.847Z
A few months ago sth in my power supply went wrong. It fried my MKS board and stepper drivers. I replaced them and I connected power supply earth to ground because I found some current leak in the Aluminum structure of the printer... I guess that was the reason it fried my board. Since then I have this problem randomly, sometimes. But now it is happening every time!
2012User
CC BY-SA 4.0
2021-09-13T08:09:58.907Z
So you have this issue since you swapped hardware, but now more frequently, did you replace the PSU and board (and stepper drivers). This does sound like a hardware failure, please check, replace and re-seat cables and connectors. Personally I would have bought another controller board and rewired the printer to be sure. This is most likely not a firmware issue.
0scar
CC BY-SA 4.0
2021-09-13T12:42:13.710Z
I replaced Board and drivers. didn't replace the PSU. It was happening frequently but it's been a while that happens every time and I can't print anything! still I'm not sure it is because of hardware failure only.
2012User
CC BY-SA 4.0
2021-09-13T16:43:06.273Z
I have a PNP proximity sensor with a 7805 regulator... inverted logic in marlin. Using M119 z probe is open before z homing, gets triggered after, even though sensor led is off. It keeps being triggered!!!
2012User
<diy-3d-printer><bed-leveling><z-axis><z-probe>
Z homing problem; starts printing in the air
2012User
# Z homing problem; starts printing in the air

(Asked by: username_0 on 2021-09-12)

I have a DIY 3D printer with Marlin firmware. I use an LJ12A3-4-Z/BY sensor for the Z probe. Recently I have had a ridiculous problem with Z homing.

In doing **Z homing**, it senses the bed, goes up, and stops, it doesn't go back to the bed...

In doing **Bed leveling**, it goes up without sensing the bed and in the next step goes even higher and higher.

If I ignore bed leveling, it starts printing in the air. If I still use bed leveling, the Z axis moves in long courses in every layer.

It looks like it is saving the wrong Z-axis position as home! These are some related settings that I think of:

```
#define Z_PROBE_OFFSET_FROM_EXTRUDER 0.25   // Z offset: -below +above  [the nozzle]

```

and

```
// Travel limits (mm) after homing, corresponding to endstop positions.
#define X_MIN_POS -3
#define Y_MIN_POS -3
#define Z_MIN_POS 0

```

and

```
// For M851 give a range for adjusting the Z probe offset
#define Z_PROBE_OFFSET_RANGE_MIN -20
#define Z_PROBE_OFFSET_RANGE_MAX 20

```

**Tags:** diy-3d-printer, bed-leveling, z-axis, z-probe

> **Comments:**
> **username_1**: What changed to have this happen? Did you change anything? Have you checked and replaced cables, remounted cables to the printer board?  
> **username_0**: A few months ago sth in my power supply went wrong. It fried my MKS board and stepper drivers. I replaced them and I connected power supply earth to ground because I found some current leak in the Aluminum structure of the printer... I guess that was the reason it fried my board. Since then I have this problem randomly, sometimes. But now it is happening every time!  
> **username_1**: So you have this issue since you swapped hardware, but now more frequently, did you replace the PSU and board (and stepper drivers). This does sound like a hardware failure, please check, replace and re-seat cables and connectors. Personally I would have bought another controller board and rewired the printer to be sure. This is most likely not a firmware issue.  
> **username_0**: I replaced Board and drivers. didn't replace the PSU. It was happening frequently but it's been a while that happens every time and I can't print anything! still I'm not sure it is because of hardware failure only.  
> **username_0**: I have a PNP proximity sensor with a 7805 regulator... inverted logic in marlin. Using M119 z probe is open before z homing, gets triggered after, even though sensor led is off. It keeps being triggered!!!  

---

## 0 answers

