5V pin reads too low with external power supply, arduino not working.

Hi all,

I have the following setup with these symptoms:

1. USB connection, no external power supply: blink example works. 5V-GND reads 5V
2. External power (12V) via ramps 1.4: led blinks fast and randomly. 5V-GND reads 3V, and VIN-GND reads 12V.

In setup 2, the original code we're using is also not working (running a fan, running steppers, etc... )

What can cause this behaviour? And can I test on something if there is something broken?

There are no stepper drivers or other components connected, and it used to work.

Thanks!

... wrecked voltag regulator? ... shorted REF-pin? ... defective stepper driver? ...

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Viktor
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Hi viktor,
Thanks for your answer.

The stepper drivers are currently unplugged.

Is there a way to test for the other 2 issues?

Thanks,
Patrik

Quote
patrik_g
Hi all,

I have the following setup with these symptoms:

1. USB connection, no external power supply: blink example works. 5V-GND reads 5V
2. External power (12V) via ramps 1.4: led blinks fast and randomly. 5V-GND reads 3V, and VIN-GND reads 12V.

In setup 2, the original code we're using is also not working (running a fan, running steppers, etc... )

What can cause this behaviour? And can I test on something if there is something broken?

There are no stepper drivers or other components connected, and it used to work.

Thanks!

If you are using a graphical LCD or servo powered from the 5V rail, then that's a known issue with Arduino/RAMPS. [reprap.org]

Edited 1 time(s). Last edit at 11/20/2018 03:14PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

That's not the case I'm afraid, we only have 2 steppers, 1 fan and 2 endstops on the ramps itself.

Is your 12V power supply putting out 12V consistently? Are the connections between it and the RAMPS secure? Is the 5V regulator chip on the Arduino getting hot?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

"External power (12V) via ramps 1.4: led blinks fast and randomly. 5V-GND reads 3V, and VIN-GND reads 12V."

The 5v regulator on the mega is damaged, its only used when the dc jack or vin is used, when exclusively usb is used 5v is taken from the computer

this is often caused by a 5v to gnd short, often from putting switch based endstops on backwards (connecting 5v to gnd via the switch)

Completely remove the ramps, apply 7-12V to the mega dc in jack (or vin pin) check 5v line for 5v. I suspect you will still get 3v... and that confirms it is not something on the ramps dragging 5v low.

Edited 2 time(s). Last edit at 11/21/2018 04:37AM by Dust.

The 12V seems stable, I checked it on the screws on the ramps. Then i also assume the connection is secure.

@Dust I tried that, and indeed there is only 3V output in this case.

Thank you all for the information, I'll replace the arduino and keep this one for usb-only applications.