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[on:]

Hey guys, first post. Bummer it has to be under these circumstances!
I created a battery charger in which the Arduino would use a voltage divider to read the voltage of the 9V connected to the vin pin. Everything was working perfectly, until it wasn't. Suddenly the vin pin no longer works, but the circuit still works when plugged into USB power. Vin won't power the arduino even when it's just straight into the battery with nothing else plugged in.

I'm not sure what happened, the only possibility I can think of is that I may have inadvertently switched polarity on the vin pin

Is there any way I can diagnose/repair or work around this?

Thanks,
Duane

[Reply #1 on:]

Perhaps you just blew the reverse polarity protection diode?
Print out the schematic and take some measurements carefully, see if Vin is making it thru anywhere.

[Reply #2 on:]

Thanks CrossRoads, I'm studying the schematic now, but I must admit I'm not quite understanding where vin would get through. I must be reading it wrong, it can't just stop in the power bus. Any tips?
Here is the link I'm looking at, I see vin in the power block toward the middle of the image. http://brittonkerin.com/annotateduino/arduino-uno-schematic.png

[Reply #3 on:]

Here is the link I'm looking at, I see vin in the power block toward the middle of the image.

It's used in two places in the upper part of the schematic, if feeds the voltage divider resistors in the auto-voltage switching circuit at the upper left, and it's feeds the on-board +5vdc voltage regulator input shown in the upper right of the drawing.

Lefty

[Reply #4 on:]

Thanks Lefty. From what I'm able to discern from this drawing (which isn't much, shamefully), I should be getting 5V from the 5V out pin when the VIN is connected to a battery. Testing concludes I am not.
I'd like to test closer to the pin, but I can't seem to determine where the components on the diagram are on the actual board.

[Reply #5 on:]

but I can't seem to determine where the components on the diagram are on the actual board.

Then down load the free version of Eagle, download the PCB layout and look. That will tell you where the parts are.

[Reply #6 on:]

Thanks GrumpyMike. I have downloaded Eagle and traced the problem to IC1. I can get 9V from there but not beyond that.
What can I do?

[Reply #7 on:]

So it's just dead I guess? Anything I can do?

[Reply #8 on:]

I can get 9V from there but not beyond that.
What can I do?

Well that means that either U1 is broken or the load on it is a short circuit.

Is it getting hot? If not then it is probably broken and needs replacing.
If it is getting hot then the problem lies down stream of this.

[Reply #9 on:]

Nope, it's not getting hot at all. How would I go about replacing U1? Would it be worth it?

[Reply #10 on:]

You need to remove the old one and fit a new one.
As it has a tab you are best using a hot air gun. Or you could snip the two legs with a fine pair of side cutters and try a big soldering iron. However it is a bit tricky, maybe you would be better off trying to find a local hack space.

You could always sell it on eBay, but describe the fault accurately.