<p>It could be a hardware fault. </p>

<p>First check, and compare, the control board connections to the motors of the three axes. You don't state it in your question but, presumably, the X and Y axes move correctly? If so, then compare the connections for the Z-axis motors with the connections for the motors of the axes that work as expected.</p>

<p>If they are correct then the problem is likely to be with the firmware.</p>

<p>Have you...</p>

<ul>
<li>homed the Z-axis yet?</li>
<li>installed the endstops?</li>
</ul>

<p>From <a href="https://makerware.thingiverse.com/groups/prusa-i3/topic:7370" rel="noreferrer">X Y Z axis only move one direction?</a>:</p>

<blockquote>
  <p>Using Marlin? Before you do a <code>G28</code> homing the axes will only move
  towards the endstops. But also check your endstops with <code>M119</code> to make
  sure they are triggered at the right time. On older Marlin, you may
  need to set <code>DISABLE_MAX_ENDSTOPS</code> (on a machine that has no max
  endstops). Newer Marlin uses <code>USE_XMIN_PLUG</code>, etc., to specifically
  set which endstops are connected. If the switches show the opposite
  state (off when triggered) then set the
  <code>[XYZ]_(MIN|MAX)_ENDSTOP_INVERTING</code> flags, as needed.</p>
</blockquote>

<p>Likewise, from <a href="http://www.instructables.com/id/Building-a-Prusa-i3-3D-Printer/" rel="noreferrer">Building a Prusa I3 3D Printer</a>:</p>

<blockquote>
  <p>You will probably also find the motor will turn only in one direction. This is normal for now as we don't have end-stops installed and haven't homed the axis - so the software doesn't know how far it can go in one direction or the other.</p>
</blockquote>

<hr>

<p>As Mark states in his <a href="https://3dprinting.stackexchange.com/questions/4158/prusa-i3-z-axis-only-goes-down-even-on-up-command#comment5758_4162">comment</a>, the P802M uses a Melzi board. From <a href="https://github.com/repetier/Repetier-Firmware/tree/master/boards/Zonestar%20P802M" rel="noreferrer">Github: Repetier-Firmware/boards/Zonestar P802M/</a>:</p>

<blockquote>
  <p>There are some printers sold under different names like 'Zonestar
  P802M', 'Prusa i3 P802M DIY kit', 'Anet A8-B', etc, which have LCD
  20x4 with 5 keys controller connected to Melzi V2.0 board via 10 wires
  cable. Keys are connected to a single analog input using resistive
  divider.</p>
</blockquote>

CC BY-SA 3.0
2017-05-30T12:41:20.620Z
2017-05-31T01:34:30.007Z
2017-05-31T01:34:30.007Z
Greenonline
<p>Thank you guys, it took me a while but it was a faulty cable, 
One stepper motor worked but the other did not. But, apparently, both have to work for even one to turn. </p>

<p>The cable had one wire isolation still in place, so there was no connection from the board to the stepper. </p>

<p>I also had another cable with the wires connected in the wrong order, as well.  </p>

<p>Bottom line - it is working. And printing well. </p>

<p>Now it seems like I have problem with the z-sensor (stopped working after a few hours of printing). But I'll figure it out tomorrow. </p>

<p>Thank you for your help.</p>

CC BY-SA 3.0
2017-05-31T18:18:39.563Z
2017-06-01T19:38:51.043Z
2017-06-01T19:38:51.043Z
Avshalom Mizrahi
<p>I have just finished building a Tronxy P802M Prusa i3.</p>

<p>When I try to move the Z-axis, using the hardware buttons in the LCD menu (without a computer connected), it only goes down, when I both increase, and decrease, the value of Z.</p>

<p>Any suggestions?</p>

CC BY-SA 3.0
2017-05-30T14:23:10.813Z
See similar issue at https://3dprinting.stackexchange.com/questions/4090/my-prusa-i3s-z-axis-will-only-go-up/4091#4091
markshancock
CC BY-SA 3.0
2017-05-30T16:26:45.100Z
Increasing the value of Z makes it go down as well? Does it make any unusual noise? I had to loosen the nut on the right lead screw, otherwise the right motor wouldn't turn when I increased the value for Z
Davide
CC BY-SA 3.0
2017-05-30T16:49:37.980Z
@markshancock - I thought that was similar too, except in this case it moves down for *both* up and down commands, which is odd.
Greenonline
<printer-building><z-axis><tronxy-p802>
Prusa i3 Z axis only goes down (even on up command)
Avshalom Mizrahi
# Prusa i3 Z axis only goes down (even on up command)

(Asked by: username_0 on 2017-05-30)

I have just finished building a Tronxy P802M Prusa i3.

When I try to move the Z-axis, using the hardware buttons in the LCD menu (without a computer connected), it only goes down, when I both increase, and decrease, the value of Z.

Any suggestions?

**Tags:** printer-building, z-axis, tronxy-p802
> **Comments:**
> **username_1**: See similar issue at https://3dprinting.stackexchange.com/questions/4090/my-prusa-i3s-z-axis-will-only-go-up/4091#4091  
> **username_2**: Increasing the value of Z makes it go down as well? Does it make any unusual noise? I had to loosen the nut on the right lead screw, otherwise the right motor wouldn't turn when I increased the value for Z  
> **username_3**: @markshancock - I thought that was similar too, except in this case it moves down for *both* up and down commands, which is odd.  

---

## 2 answers

### Answer by username_3 on 2017-05-30. Score: 4

It could be a hardware fault.

First check, and compare, the control board connections to the motors of the three axes. You don't state it in your question but, presumably, the X and Y axes move correctly? If so, then compare the connections for the Z-axis motors with the connections for the motors of the axes that work as expected.

If they are correct then the problem is likely to be with the firmware.

Have you...

* homed the Z-axis yet?
* installed the endstops?

From [X Y Z axis only move one direction?](https://makerware.thingiverse.com/groups/prusa-i3/topic:7370):

> Using Marlin? Before you do a `G28` homing the axes will only move
> towards the endstops. But also check your endstops with `M119` to make
> sure they are triggered at the right time. On older Marlin, you may
> need to set `DISABLE_MAX_ENDSTOPS` (on a machine that has no max
> endstops). Newer Marlin uses `USE_XMIN_PLUG`, etc., to specifically
> set which endstops are connected. If the switches show the opposite
> state (off when triggered) then set the
> `[XYZ]_(MIN|MAX)_ENDSTOP_INVERTING` flags, as needed.

Likewise, from [Building a Prusa I3 3D Printer](http://www.instructables.com/id/Building-a-Prusa-i3-3D-Printer/):

> You will probably also find the motor will turn only in one direction. This is normal for now as we don't have end-stops installed and haven't homed the axis - so the software doesn't know how far it can go in one direction or the other.

---

As Mark states in his [comment](https://3dprinting.stackexchange.com/questions/4158/prusa-i3-z-axis-only-goes-down-even-on-up-command#comment5758_4162), the P802M uses a Melzi board. From [Github: Repetier-Firmware/boards/Zonestar P802M/](https://github.com/repetier/Repetier-Firmware/tree/master/boards/Zonestar%20P802M):

> There are some printers sold under different names like 'Zonestar
> P802M', 'Prusa i3 P802M DIY kit', 'Anet A8-B', etc, which have LCD
> 20x4 with 5 keys controller connected to Melzi V2.0 board via 10 wires
> cable. Keys are connected to a single analog input using resistive
> divider.


---

### Answer by username_0 on 2017-05-31. Score: 3

Thank you guys, it took me a while but it was a faulty cable,
One stepper motor worked but the other did not. But, apparently, both have to work for even one to turn.

The cable had one wire isolation still in place, so there was no connection from the board to the stepper.

I also had another cable with the wires connected in the wrong order, as well.

Bottom line - it is working. And printing well.

Now it seems like I have problem with the z-sensor (stopped working after a few hours of printing). But I'll figure it out tomorrow.

Thank you for your help.


---

