Reply To: Tin's 1100x900mm Build

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Martin S

Everything was going really smooth, but the other day I fried my Arduino Mega. I don’t know if I did something wrong or if it’s a hardware issue.
I will try to explain what I did. Sorry if it’s not proper English.

1). Mounted the Ramps on top of the Mega.
2). Put the jumpers, all 9 of them to get 32 steps.
3). Connected the Ramps+Mega to the PC with the USB port (12v PSU still not connected).
4). Loaded the firmware.
5). Unplugged the USB and placed the DRV8825 drivers.
6). Turned on the Ramps+Mega using just the 12v PSU and then calibrated the drivers.
7). After that, I plugged the USB to the PC. At the exact moment I’m doing this, the notebook turns off.

* The Mega is no longer recognized by the PC.
* The 2560 chip was extremely hot, to the point of burning when touching.
* I can’t recall, but I think that the USB port of the Megas was hot too.

I’ve already bought another Mega, but I’m scared of connecting it, before knowing what went wrong with the other one.

Stuff checked with the new Mega:
A). The output voltage of the 12v 20a PSU is 12,23vDC with no load.
B). With Ramps+mega connected to the PSU, but unplugged from the PC, the output voltage of the Mega’s USB is 6,28vDC. Shouldn’t this be 5vDC? If I raise the voltage of the PSU, the USB also rises.
C). I measured the ground to ground voltage between the PSU and the Mega USB and it’s zero. So there is no voltage difference.
D). Then I checked for continuity between the -V of the PSU and the ground (earth) of the mains cable and it doesn’t “beep”, neither does the +V so there is no continuity.
I read that to fix this -V line floating, I need to bridge one the -V to the ground terminal.
Is this the right thing to do? I know nothing John Snow.