PC shuts down when I connect 12V

Hi All,
I'm really enjoying building my DIY Prusa i3 although it is taking a long time.

I have obviously damaged something via a short circuit, whilst probing with mutimeter I think.

I originallyconnected the ramps to the arduino and tried to install Sprinter. But Sprinter download from Github would not download so I changed to Marlin which compiled properly and uploaded to the arduino.

I also installed Pronterface and all seemed well.

Unfortunately pronterface showed errors so I assumed it was the baord at fault and started poking around with a mutimeter to try and measure voltage between Gnd and the Pololu pot. I slipped and shorted something around the PSU area. PC went off.

Rebooted PC reconnected 12V and off again.

Rebooted PC and connected RAMPS via USB only and all seems well. I can measure both thermistor values and all three End Stops show up nicely with the M119 command.

So most if it works but the 12V don't.

I bought a new RAMPS board but the same thing is happening, shut down when connecting 12V.

I've measured my 12V and it's reasonable (from an ATX PSU).

Do I have to buy a new Arduino Mega or is there soething I can just replace?

I am sure the answer is to buy a new Mega but if anyone has any other ideas to save a few quid I'd be pleased to hear them.

I would say you probably have a short to ground somewhere in your RAMPS. To check:

1. remove all the connectors and the stepper drivers from the RAMPS board, i.e. just leave the Arduino and the RAMPS.
2. Connect only your power supply to the RAMPS and turn it on.
3. If you still have a short, your PC will turn off. Change the RAMPS.
4. If you do not have a short now, re install the drivers and connectors one by one. Sooner or later you'll get the same problem and voila, you have identified the source of your problem.

What I do not understand is why even a short on your RAMPS could cause the PC to power off? Your RAMPS is connected to its own power supply, not the one from the PC? Then your only connection between the PC and the RAMPS is via the USB port and that one is protected against shorts.

Could it be that your problem is due to some ground loop? Do you have the PC and the power supply of your i3 on the same phase of the mains fuse? If you measure the voltage between the PC ground and the RAMPS ground (PC *not* connected to the i3!), what does read?

normaly its two much current been drawn from the pc (ie a short somewhere)

Or in this case a short from 12v to 5v somewhere.. most likely a dead or pugged in backwards pololu module.

But with these ultra cheap ramps kits with zero checking... could be anything



Basic diagnosises

remove all pololu modules, power it on, does it still do it? if so bad ramps, lok for bridged solder joints, incorrect componets etc
If no the its a bad pololu or it was plugged in wrong, backwards, one pin over or just dead.