RAMPS hangs and shuts down when heating extruder

Hi All,

I'm currently building my second printer. In my first, I was using Melzi board because I bought a kit. This time, I'm building from scratch and using Arduino Mega + RAMPS. My printer model is Prusa i3 with dual extruder.
What's weird is this:
Firstly, I was testing my one of my extruders to do several prints, and had undergone heating for several times. And it was all OK.
Then I tried the other extruder. When it was heating alone, with all other things off, it was fine. But the moment it's printing second layer and the fan went on, the temperature drops from 200'C to like 170'C and the printer immediately hangs and shuts down. The logs in Repetier-Host said "connection timed out".
I thought my ceramic heater was the cause because it is an old heater and had once smoked because the thermistor was loose.
But, changing the heater to a more normal one made no difference.
Then I swapped the extruder cables (extruder 1 <-> extruder 2). No difference. The same heater cause the same problem.
Now, I detached one of my heater. When I turned on the detached heater (and nothing heats up of course), it also shuts down after a moment. Note that now the detached heater is #2 (the once-smoked one) and the attached one is #1 (new) connected to slot #2 on RAMPS.
Now both causes printer to shut down.
Any hints?

Thank you very much.

"Now, I detached one of my heater. When I turned on the detached heater (and nothing heats up of course), it also shuts down after a moment" - How long is a moment?

Nonetheless, how hot is the components getting on your RAMPS board? Can you touch the two big yellow fuses? How about the MOSFETS driving the hotends, are they super hot?
If they are, try aiming a fan on them to keep them cooler.

I do not know what is wrong, but from the symptoms you mention (time - after a short while it stops working. And only once you added a second hotend, which means more load to your PSU) it seems like it is a power issue.
I would check the "wiring" of the RAMPS board (around the drivers) and see if there are any shorts. Also, I am not sure what the board would do if you tell it there is a second hotend connected to the board (even though there is nothing connected), maybe it tries to heat up .. well nothing.
Did you disable the second hotend in the firmware when you detached the one hotend?

Hopefully this helps you at least a little bit.

Good luck.

Edited 1 time(s). Last edit at 06/21/2016 08:08AM by v1talogy.

Please do not forget to test your PSU! Sometime the problem can come from bad PSU that shutdown with a lower load than what they are rated.

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DYZE DESIGN
Hotends, Extruders, Liquid Cooling and Accessories.

If you are running your fans off of 5 volts. The Arduino Mega may not have enough current for it all. You may need a separate additional 5volt power supply.