Melzi V2 board on Prusa i3- commissioning
September 20, 2015 07:02AM
Hi All.

This is my first 3d printer project and am having some problems getting everything working.

Everything is build and (as far as I can tell) correctly wired up.

When I power up the unit, the led on the power supply lights up (and this stays on). There is also a LED on the Melzi board (L1) that lights up red for about 3 seconds before going out. At the same time that L1 lights up, the extruder fan becomes active. The fan also stops when the the L1 LED goes out. While it's active, there is 12V across the fan connector on the board which drops to 0V when the fan stops. Once the fan has stopped, there is still 12V supplied to the board.
This doesn't seem like correct behaviour but I don't really know. Can anyone offer any suggestions or provide a set of things to test in order to see what's going on.

When the board LED goes out and the fan has stopped, it is possible to start the cycle again by pressing the 'reset' switch on the board. The LED lights up and the fan starts again (but only for the 3 seconds and then everything stops)
JMP15 isn't set to USB
I have installed RepetierHost on the PC but don't really know if the printer is recognised properly. I can press the 'connect' icon on top left of screen and it goes green and says connected but if I manually try and move the bed or extruder, it just queues the commands and nothing happens. Of course, by this point, the LED on the controller board has already gone out.

Any help greatly appreciated or I can supply pics/screenshots if someone can tell me what relevant information to post.

Re: Melzi V2 board on Prusa i3- commissioning
September 27, 2015 05:31PM

I have exactly the same problem. My power supply seems OK (fans can turn if directly plugged to it) but I have the same voltage drop on melzi board when I plug the printer.
I can add that I can hear that the PC detects the printer (the windows noise), but impossible to communicate with repetier.

Like Richstuch, I will be very grateful if you could provide me some informations on how to solve this pb^^.

Re: Melzi V2 board on Prusa i3- commissioning
September 28, 2015 03:01AM
Are you sure that what you are seeing in the first 3 seconds after powering on is not just due to the boot process, i.e. just happening in the time between power on and the firmware starts controlling actively the pins? I don't have a Melzi, but also on my Sanguinololu the fan turns for a few seconds before Marlin has bootet and switched if off. And the LED on the RAMPS also blinks for a second or two at power on. So maybe your problem is not related to what you see and measure in the first 3 seconds after powering on...

What firmware do you have installed on the Melzi? And is it configured correctly? Is the baud rate configured correctly?
Re: Melzi V2 board on Prusa i3- commissioning
September 28, 2015 07:04AM
thx for your anwer Enif. Actually I bought my printer from aliexpress (Hesine 3D prusa i3). They are supposed to be plug and play and I do not know what firmware I have. I already asked to the seller and I am waiting for an answer. Baud rate is 250000 in repetier.

In fact even after the lights turns off, I am unable to use it with repetier, I have a connexion error when I try to connect (error serial communication/Forcing start), and I can not move anything on the printer.
Re: Melzi V2 board on Prusa i3- commissioning
September 28, 2015 07:19AM
Thanks for the replies. I now realise that my issue was due to my noobness. But for info of others that might be having similar problems, I thought I would post what I found out and how I got mine to work in the end.

As pointed out, the fan starting for a couple of seconds, the LED lighting for a few seconds before going out is just the normal boot sequence. What made me think it wasn't working properly is the lack of connectivity to Repetier or Pronterface. I did a couple of things to resolve:

1. I updated to the latest Virtual COM port drivers and FT232 USB drivers. Available here - [] ( this will be the cause of improper recognition of the printer and will show errors in your 'Device settings' (for Windows) if they are not up to date)
2. Changed the baud rate from the default 256000 to 115200

Once that was done, successful connection was made at first attempt. Just make sure you note which COM port gets added by the drivers. I installed on 2 PCs and one of them got COM4 and the other COM5. You can then select that in the connection settings ('Auto' might work too)
Re: Melzi V2 board on Prusa i3- commissioning
September 28, 2015 07:28AM
I think that you should insist that your seller sends you the configured(!) source of the firmware for your printer. Because without it, you won't get far anyway. Sooner or later you want to do some upgrade of hardware or software, and then you'll need to be able to flash the firmware again. If your seller does not want to give you the configured source code, you will be better off to install a fresh open source firmware from scratch, and calibrate your printer yourself. It's a learning experience, but you'll find whatever you need on wiki and forum - and it's well worth the effort, believe me smiling smiley

Glad to hear that you got it working now!
Re: Melzi V2 board on Prusa i3- commissioning
September 28, 2015 06:16PM
Hello all,
a bit late compared to Richstuch but the baud rate was also the solution for me! When I set it to 115200 it works immediatly.

@Enif: I think you are wright, I will try to reflash a new firmware as soon as possible (I realyy would like to know what is behind the control of the printer) but nobody can resists to print his first part before working on that kind of things grinning smiley.

Thanks you Enif and richstuch!
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