Fried RAMPS 1.4 after replacing hotend

Hello,

I have an old pre-built ramps 1.4 reprap that's never properly worked due to clogs (no issues related to heaters or the board before though).

I recently replaced the whole current dual-extruder setup with a new 12v single hotend. After wiring up the new heater and thermistor, I flashed updated firmware to the board and ran a pid tune on both the extruder and bed heater. This seemed to go as expected, the only issue I encountered to this point was the bed refusing to heat (returning a min temp error) if I attempted to set the temp to >50c. I attributed this to a config issue and continued the bed tune at 50c. After updating the pid values for both heaters I loaded a calibration cube and began the print. The axis all successfully homed and the print began just fine until I noticed the bed had been put out of level. I stopped the print and powered the machine down before proceeding to level the bed. After that I turned the machine back on and attempted to home the nozzle to check the level to find that all of the stepper motors were not energised at all. I then attempted to heat up both the hotend and the bed and both gained no temperature before returning heating failed.

At this point I checked the thermistor readings and found they were reporting the ambient air temperature with frequent small fluctuations, which suggested to me they were working. Next I loaded up the reprap test code to check the led responses and eliminate firmware issues. The board connects just fine and the led blinks during communication. Once the test code was loaded, the communication led began to blink but none of the others showed anything (aside from the constant red). I also noticed that the fans in the board housing were not spinning, so I checked where they were supplied and they were plugged in to the 12v input, along with the psu out wires. At this point I figured I had either fried a mosfet, or the 12v input pins. I don't have a multimeter handy so I cannot diagnose much further right now and I am completely unequipped to replace components on the board itself, so I decided it was likely the arduino had survived and that it made more sense to replace the shield with a ramps 1.6 than waste hours diagnosing and spending 3x on equipment for board-level repairs.

Does anyone have an idea as to what might have fried in the board based on this info? The replacement hotend is within spec (12v, 40w, 100k ntc) so I'm not sure how that could have overloaded the board. As I say I'm going to swap the ramps for a 1.6 anyway, but I really don't want to start just chain-frying boards. I'm not sure what could have gone wrong and whether it will insta-pop the new ramps as soon as i connect it. Any knowledge or advice is appreciated.

Thanks for your help!

Edited 1 time(s). Last edit at 10/07/2022 08:27PM by sundaycrunk.

Having a low-cost multimeter will always be a good tool to have, if you want to troubleshoot or debug any kind of electric issues on a 3D printer.

And it may very well be the (simple) tool that will prevent you from chain-frying RAMPS boards.