Melzi connection/freezing help

I have a RepRapPro Tri-color printer with dual Melzi controllers. I did love it up until a few days ago.

It started doing this thing where the printer loses connection with the computer mid way through prints. The printer freezes and the pronterface cant read or right. If I click 'disconnect' in pronterface to reconnect then pronterface becomes (not responding) and wont close. If I open a second pronterface and try to connect then it responds that the access is denied. The hot end and bed continue to maintain their correct temperatures the whole time. I have to unplug the power to the printer and plug it back in to reconnect.

It seems to be completely at random. I cant quite tell for sure but it looks like its in the middle of moves some times. Meaning that its probably not a communication issue on the computer side. not sure though. I made sure that its not the usb cable the best i can. If i move it around I cant make it freeze. It seems to be getting progressively more common. Now i cant finish any prints.

I have read that sometimes power surges can cause strange things but it even does it late at night when nothing in the building is on (i have it at work).

It does one thing that i have noticed. When the board is running normal it blinks at a stead quick pace. Once it freezes it changes to a combination of short and long blinks. I tried to find a pattern but it seems to be random. its mostly long blinks with some short blinks here and there.

Could it be an overheating issue? Is there any way to check that?

Is the board bad?

Any help/advice is greatly appreciated!!

-Brad

i dont know why but this reminds me of a issue where your grounds on your reprap ps and computer are not grounded at the same level.

dose it have the same issue with the reprap ps turned off / disconected.?

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[mike-mack.blogspot.com]

dissidence, do you mean with the board running the board on usb power?

Thats a good point. Now I am running the machine but with everything off. No heat or printing. I will let that run for a while and see if it freezes with nothing printing. If it does than I will repeat it with only the board on USB power.

Ya that's the idea to see if it might be a issue between your computer PS and reprap PS.

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[mike-mack.blogspot.com]

So I let it sit on with the regular PSU for a while and it did freeze at one point. It was about 1-2 hrs before it frooze. I'm not sure I didn't watch the whole time.

Then i switched the jumper to usb power and dis-connected the PSU. I let it sit for several hours and it didn't freeze. Im still not sure that the ground problem is the answer but how do you eliminate it as a possibility? Both plugs are on the same circuit so i feel like grounding the grounds is a little redundant, but maybe not? should i wire the building ground to the negative on the reprap?

I upgraded my mono mendel to a tricolour over the weekend and I am having a similar problem.

I thought it was a short so I stripped it down and rebuilt it, testing everything as i went along but its still happening.

I then ran some tests by setting the standby and operating temps of the hot ends (G10 P0 X0 Y0 Z0 S205 R180), long story short I can either have the hotends on or the heat bed. I have an efuel 20 amp power supply and it tells me the current draw everytime it bombs out its shooting up to the max current and I also Over Current Errors (OCP).

Have the hotends on and the hotend fans draws around 8.9 amps. The Heat bed seems to draw around 11.3 so it seems to be that there is too much current draw for the power supply.

I also updated my firmware to the latest version on both Melzi's before this started happening.

I am considerring power each Melzi seperatly until I can spring for a 40 amp power supply but I not sure if this would short out anything!

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www.ur3d.ie
www.keschka.co.uk

I am now also having a similar problem, the printer has been working fine for about a month, last night about an hour before the end of a 5 hour print I noticed the Pronterface was disconnected. the printer was still printing from the SD card though. When I tried to reconnect it said " can't connect to port COM7, Access is denied" now I have to reset the computer and the printer. I then start pronterface back up it works fine for a minute or two if it disconnects in the middle of homing it freezes if not it just looses connection and comes up " can't connect to port COM7, Access is denied" this is really annoying everything was working fine before and I do not understand what could have changed. When I put the board to USB mode it seems to connect fine even if that error has been coming up before switching to USB.

My Reprap is a Tri-colour Mendel.

I still havent resolved mine yet either. I have been speaking to Ian at RepRapPro and it looks like the restance of my heatbed is too low. It should be 1.3 ohms and mine is 1ohms. The lower the resistance the higher the current.

In my case my heatbed heats up supper quick but this quick heat up means that its drawing too much juice (11.3amps in my case) this is causing we Melzi to disconnect from the computer as the combined load 11.3 for the heatbed and ~3.5 for each of the hot ends equates to more than 20amps.

EDIT: Here is an alternative 30amp power supply that might do the trick: [www.amazon.co.uk]

Edited 1 time(s). Last edit at 08/02/2013 07:08PM by ur3dchef.

Thanks for the update man have you tried running with the heatbed of does it work ok then?

Aye, if i run with just the hotends on its fine.

Does your heatbed heat up quickly?

I read somewhere it normally take around 20 minutes to get to 57 degrees but I can't confirm this. Mines normally takes around 10~ min to get to 62!

I will try that tonight as admittedly I usually turn the heaters on first when it starts up so it could be that causing it.
But its been fine for over a month not sure how the resistance could drop more chance of it increasing I would have thought.

Thanks though I will update as soon as I get a chance to try.

OK so its started and homed OK without crapping out when I do not turn the heat-bed on. I have also noticed my heat-bed is measuring about 10 Degrees hotter than it should be...
I'm fairly confident its to do with the heat-bed now will try a print with it off and see.

Have you tried measuring the resistance of your heatbed?

just checked there its about 1 ohm as well. I don't understand how it can change though its been working fine for a month or so. Have you tried the higher current power supply yet or what are your plans?

I tried powering the 2 Melzi boards off 2 different 20 amp power supplies (I wanted to make sure power was the issue) it power all the heaters and the bed without issue.

I had other issues with this setup in that the 2 boards wouldnt talk to each other properly (I think this may have been done to some sort of sync between the boards by using 2 seperate power supplies), however it prooved the point I had everything on hotends at 180 standby/205 Service and the heatbed at 62 degress and I could print way past the point where it would normally fail.

I am going to hold out for a month and buy a proper power supply. I have been using this [www.skyrc.com] power supply on my RepRap and it has been great. I'll probably upgrade it to the 30 amp version.

I am only running one hotend and board just now though so it should not be close to its max.
I will try a bigger power supply though. Will there be no issues with it drawing too much current?

If your only running 1 hotend and the heat bed the current should be around 13.5 to 14.5a at 12volts.

I like the efuel PSU as you can monitor current flow and adjust the voltage on the fly. I have my PSU set for for 12.5 volts and it like a charm.... that is until I attach the 2 further extruders (7amps) which gives 21.5 amps!