Print Stops Midway Through

After printing happily for weeks - over USB - today the printer stopped 3/4 way through a print much like the jobs it had no problem doing previously. There were no error messages in the Pronterface output window. The fan remained on but I could send no commands through Pronterface. So I turned off the Mendel90 and after turning it on again connected to it as normal. When closing Pronterface it generated an error. This normally doesn't happen but I have seen the error before. I restarted the computer.

These freezes have happened before but VERY rarely. I am wondering what to suspect? It seems to be obviously between the computer and printer somehow but is it the cable, or maybe Pronterface? I would like to eliminate this.

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Garry Bartsch
.... It seems to be obviously between the computer and printer somehow....

Not necessarily. It might be worth eliminating the USB connection entirely by printing directly from the SD card for a while. If the problem still arises, you have eliminated the USB connection from possible causes. If the problem goes away, THEN you can start to suspect the USB side of things. I had similar problems a while back which turned out to be a power supply problem: [forums.reprap.org]

Alan

Check the ground connection to the melzi is tight.

Unfortunately USB was a poor choice for RepRap because it only works properly when the device is isolated. When both the host and the device are grounded you get a loop that can pick up RFI. Because USB uses a none differential signalling code in an otherwise differential protocol it is susceptible to common mode noise. Because it is a connection based protocol it cannot recover seemlessly when comms breaks down like a conectionless protocol can.

To minimise ground loop pickup you need to minimise the area of the loop. I.e. use short power cables plugged into the same wall outlet and have the PC physically close to the printer. My own experience is that with a laptop next to the machine it is 100% reliable but with a desktop the other side of a room it will always fail when the room light is switched off. Those are two extremes and other layouts will be somewhere in between in terms of reliability.

The problem is completely solved if you use octoprint on a raspberry pi that is powered from the the same PSU and grounded to the Melzi. The Ethernet connection to the RPI is transformer coupled at each end so there is no ground loop, or you can use WiFi.

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[www.hydraraptor.blogspot.com]

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Alzibiff
Not necessarily. It might be worth eliminating the USB connection entirely by printing directly from the SD card for a while.

Good idea; if this starts happening more frequently I will. But honestly I can't accurately remember the last time it locked up like this. It's really been more like months (it's happened maybe five times since I've had the Mendel90). I'd have to print from the SD card for a loooooong time before I could eliminate the USB and I don't have the patience LOL.

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nophead
Check the ground connection to the melzi is tight.

Thank you. I will do this as soon as I can get some help.

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nophead
The problem is completely solved if you use octoprint on a raspberry pi that is powered from the the same PSU and grounded to the Melzi.

I started to read about RaspberryPi; that is really cool. I think it will be worth evaluating for my new machine. Now I need to research how it will tie in to RAMPS.