Recovering from wrong power connection on RAMPS 1.4

After successfully building 2 printers I managed to mess up on my 3rd Prusa i3. I connected the PSU on the RAMPS 1.4 the wrong way at first, the + in the - and vice versa.

I turned it on and nothing moved (as it should by the Marlin defaults) and after a few seconds I saw a bit of smoke and smelled. I realised what I did, reversed the black/red cables and tried again. The motors moved at first but then stopped and had the same smoke and smell come off the board. The second yellow fuse (the slightly smaller one on my RAMPS [www.reprapdiscount.com]#) was getting very very hot. I tried again and got the same issue.

Any ideas what would be burnt first with such mistake? A fuse, a diode or worse?

Thank you.

Edited 1 time(s). Last edit at 06/07/2014 06:07AM by SirDuke13.

There is a reverse voltage protection diode D2

If that didn’t survive, then you could have partial short from +12v to GND threw it... this would cause F1 to get rather warm.

I would replace D2 (the one next to the fuse)

That's exactly what happened, I replaced the D2 diode with a new N4007 one (I could not find a N4004 which I think was the previous one) and it works great now.

Thank you!

To follow up, everything worked with the new diode, all axes move fine and the printer extrudes etc.

However, the extruder hot end will not stop heating up, so I guess that MOSFET was also damaged (the heated bed MOSFET works fine). I'll replace and see if that fixes it.

if the nozzle heater won't turn off then it's shorted. When those fail, they fail shorted (always on).

I'm having an issue with my heater bed doing the same thing. Replaced thermistor just cause I had one on hand and still as soon as printer is powered up heat bed is on and wont shut down. I've thoroughly checked for loose, broken or frayed wires and suspect the ramps board itself, not knowing much about how the polyfuses work. I assume theyre normally closed and open on over amperage? Any input appreciated, thanks.

Edited 2 time(s). Last edit at 06/12/2014 10:54AM by cool2print.