Fix an Arduino That Only Works Via USB (blown Regulator)




Introduction: Fix an Arduino That Only Works Via USB (blown Regulator)

It's happened to everyone, you accidently plugged something in wrong or pulled too much current through your arduino. Afterwards, you heard a pop, got that wonderful burnt out electronics smell and a whiff of smoke. You probably think you just fried your arduino, but that may not be the case.

This guide specifically applies to an Arduino Mega 2560 (from eBay) but may work with other boards like a Uno etc. It will try to describe in detail how to diagnose a faulty regulator and replace it. It won't even attempt cover all the other possibilities of a dead arduino so if this isn't your problem post in the comments and I'll try to help.

Step 1: What Is a Regulator and Why Did It Fail?

I'm by no means an expert, so I'll do my best to explain what the regulator is and why it may have failed. The main job of a voltage regulator is to regulate, or limit the voltage going to a device. Many components of the arduino board and sensors you might use usually can't be exposed to the same voltage as your power source. (if you aren't using USB)

For example, the ATmega processor on your board is very sensitive to the voltage it receives. If it is exposed to more than 6v it will blow up - literally. Take a look at the datasheet (it is attached, I've also attached a summary screenshot) so you can see the various "absolute maximum ratings". Absolute Maximum means just that, this is what most datasheets will define it as:

"Stresses beyond those listed under 'Absolute Maximum Ratings' may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or other conditions beyond those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability."

So now you know what a regulator is, but why did it fail? The most common reason that I know of is you accidently shorted the 5v output to ground. This means a huge amount of current tried to flow through the regulator, burning it out. Another common reason is hooking up one or more devices that draw more current than it's rated for, like a motor. (which is basically the same as the first) You could have also plugged the power source in backwards and exposed the regulator to negative voltage - most things don't like this. There are many other reasons you could have blown up a regulator so don't fret if it wasn't one of those.

Step 2: How to Diagnose a Blown Regulator.

Before you go ordering parts and de-soldering components, it's best to make sure you actually have a blown regulator. Sometimes it will be immediately obvious that the regulator has blown. If it gets very warm when nothing else is connected or has obvious physical damage it's probably dead. Usually you will see a little burnt bubble or two, or in more extreme cases a part of it could be missing. See the photo.

If you can't see any physical damage then get out your multimeter and another arduino mega if you have one. You want to find the regulator - it's between the USB and DC Barrel Jack connectors. (see the photo) Set your multimeter onto continuity and test all the pins. The stock arduino regulator should have no continuity between any pins except for the middle one and the tab sticking out the back. If you get continuity between any other pins, you have a bad regulator.

If you still can't confirm if your regulator is dead, try leaving a comment and I'll see if I can help.

Step 3: Replace Your Regulator

If you've confirmed that your regulator is faulty, it's time to replace it. Check out eBay for some really cheap ones with questionable quality or order from somewhere like RS online. Most 5v regulators should work, just keep in mind that not all pinouts are the same. If it differs, you may need to solder individual wires back to each pad on the arduino.

The exact regulators that I used where bought from RS Online. They have a huge selection of parts and in Australia offer free next day shippinh on everything. (I bought the bag of regulators on a Monday afternoon and had them Tuesday lunch time!) Here is a link. I chose to replace it with the 7805 regulator because it's much more capable (but larger) and can be used for many other projects.

That regulator's pinout is different so you will need to bend some pins in order to solder the right ones onto the board. Take a look at the picture above, and you can see where the new pins have to go. If your interested, Vin is where your power source + goes to and the Vout is where the nice, regulated 5v comes out.

Hold it in place with whatever you have, I find it difficult to solder anything unless I have one of these "third hand" things. It makes it easier to solder if you trim the legs right down, and bend the ends flat with the board. (see the picture)

Step 4: Extras

After you solder it, you may want to bend it down out of the way. You will need to do this if you are using any shields like a RAMPS (what mine is being used for) etc. Be very careful when doing this as the pins are fragile and will break if you bend them back and forth more than once or twice. (or even if you bend them to far!)

I suggest putting a bit of electrical tape on the USB port just in case. For some regulators, it won't end well if the metal part touches it.

You may also want to put a heat sink on the regulator if you intend on drawing a large current, (0.5-1.5A) or if you have spare ones lying around not being used like I did.

Thanks for reading! If I helped save your "dead" arduino please leave a comment and favourite this 'ible. :)

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2 years ago

Hi, I had a problem with my arduino uno that looked just like this, it happened while powering a CF Sunbird microservo with the arduino feeded via USB.
I might have short circuited the 5V and GND when i connected a button, and the components i connected to arduino stopped working. The weird thing is that i measured all voltage outputs from the arduino pins connecting them with jumper wires, and they outputted and read the right voltages, but I tried connecting an LED and it didn’t light up. The board’s builtin LEDs are working properly though.
I checked the continuity in the regulator, and it has continuity only between the middle pin and the tab sticking out of the other side

Thanks in advance!


5 years ago

Thx Jabelone,
I was just wondering if this could work with the same regulator part (if you bought a new one): AMS1117 5.0? Wouldn't that be easier? I'm just curious to if there is any easier way.


6 years ago

hello jabelone

Thanks for the post. I have 5 mega's sitting around with all the same 5v problem. All were hooked up to a 3D printer at some point and inadvertently have been shorted in the 5vdc circuit. They all still work by USB but not on the 12vdc supplied by the printer power which makes the SD card useless. Anyways I purchased the 5v regulators and replaced 4 of the Mega's regulators with out checking your continuity test prior. ( just started looking for a test recently) You may know more about the circuit than me so here's my observation. Powering the Mega with the Vin pin @ 9vdc I see at the 5vdc Regulator pin 1. 0v pin 2. 2.13vdc pin3. 9vdc. In other words I'm getting only half the 5vdc from the regulator. Have you seen this before? Thanks for any help.


Reply 6 years ago


Depending on the regulator you get it might be expecting a certain combination of resistors to set the output correctly. If you got exactly the same one I linked then I'm not sure sorry. I had a quick look at the arduino schematic and I couldn't think of anything else. I would suggest posting on either the arduino or an electronics forum with the exact regulator you bought and your observations.

One other thing you could try (which I've done before) is to simply chuck a 5v source onto the 5v rail by supplying it through the 5v pin. If your printer uses an old PC power supply you can tap into the 5v rail on this or you can try putting the regulator separate from the arduino and doing the same thing. If you do this look up the data sheet of your regulator and wire the 12v to the input and the 5v pin to the output.

As a last resort or temporary work around you could use an old phone charger and plug it into the arduino.


Reply 6 years ago

Hi Jabelone
Thanks for the quick response! I did buy the exact replacement just for the reason you suggested. I can't say I know enough about the circuit to be able to buy a slightly different regulator and didn't want to also wonder if it needed additional components.
Also like you suggested I posted on the Arduino forum to see if someone else may have experienced this. Haven't had a response as yet but I just posted it last night. The link is here:
I've had 18 views but no responses yet, I figure they just don't want to talk to a Bonehead who shorted out 5 mega's or it's a difficult fix because of all the down stream components that might pull the 5vdc voltage down. Anyways again thanks for the response and posting.