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At start of print only one z axis is working

Posted by gribble 
At start of print only one z axis is working
September 06, 2017 12:52PM
Hi,
I got back to 3d printing after nearly a year a few days ago. My first prints went fine but today I have a problem and no clue how to solve it sad smiley

I still use printrun and when i start printing, my nophead mendel90 moves to the home position on all three axes just fine. Then it starts moving down the z axis and shortly after it starts moving down only one z axis motor works and the other one seems to be "blocked". I can then manually rotate the second z axis and it starts spinning... but then the first motor instantly stops. If i rotate the first one again the second one stops again ... and so on and on. It doesn't matter if I want to print through USB or from the SD card.

When using printrun manually I can move the z axis up and down just fine.
Re: At start of print only one z axis is working
September 07, 2017 01:13AM
Try turning the bed on in printrun and then moving the Z axis.

My best guess is you have a bad connection from the power supply and the 12V rail is too low for two motors in series when the bed is on.

Edited 1 time(s). Last edit at 09/07/2017 01:18AM by nophead.

[www.hydraraptor.blogspot.com]
Re: At start of print only one z axis is working
September 07, 2017 01:11PM
I turned on the bed (60°) and direct afterwards i got disconnected from the printer

Quote
printrun
Setting bed temperature to 60.000000 degrees Celsius.
Can't write to printer (disconnected?).
Can't write to printer (disconnected?).
Can't write to printer (disconnected?).
Can't write to printer (disconnected?).
Can't write to printer (disconnected?).
Can't write to printer (disconnected?).
Can't read from printer (disconnected?).

and pronterface.exe is not responding anymore sad smiley Can't even kill the process. I have to turn off the printer and then the application closes.

I then had a quick check of the melzi board and by my suprise I saw this at the power connector:


Guess I have to check and clean this (don't have time for this until next week sad smiley ) and hope it will work afterwards.
Re: At start of print only one z axis is working
September 29, 2017 08:02PM
This failure has happened to me too. I had to change the Molex connector and the printer started to working again...
Re: At start of print only one z axis is working
October 01, 2017 12:31PM
Sorry for the late response.

After changing the screw terminal everything works fine again smiling smiley

Thx alot

Quote
http://reprap.org/wiki/Melzi
Melted screw terminals
Sometimes, the screw terminals on a Melzi melt. More often than not, it's the bed terminal, and is due to the wire being poorly connected, ie loose in the screw terminal. It can also cause the MOSFET to fail, as it cannot dissipate heat generated as it switches on and off. RepRapPro advises customers to check the screw terminal connections periodically: [reprappro.com]
If the Melzi PCB is undamaged, you can simply replace the screw terminal. There are a couple of different screw terminal blocks, these are the most common:
This is the most common one - [uk.farnell.com]
this one is a bit taller, and easier to get the wires into - [uk.farnell.com]
The heated bed power cable carries about 10A at 12V, so any poor connection will tend to heat up. Check that your power and heated bed wires are stripped back far enough to go well into the screw terminals, and it's always worth checking that the screw terminals are well-tightened occasionally. Also, wire the printer with enough slack on the heated bed power wire so that it can be attached to frame, and there shouldn't be any movement of it at the Melzi end. But strain relief on any moving wire is necessary - try to make the movement in the actual wire, rather than at a connection point, to avoid the wire fatiguing.

Edited 1 time(s). Last edit at 10/01/2017 12:32PM by gribble.
Re: At start of print only one z axis is working
October 04, 2017 12:52PM
To prevent this, wind your wire tips as tight as possible and tin/seal them with some solder.
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