Location of USB fuse on Nano 3.0 board

I am 99% sure I figured out what was wrong with my Arduino Nano 3.0:

Initially I thought I fried the FTDI chip as I could power the Arduino externally and have the program work, but my computer wouldn't detect it. When I checked the 5v line when connected to USB only, though, I was only getting ~3v. Then I tried hooking it up to USB while powered externally and surprisingly my computer detected the serial port.

I figure the fuse is what was blocking some voltage from the USB line, and my computer wasn't detecting it because the signals weren't 5v. So, I need to check the fuse. I have an OSEPP Arduino-compatible Nano 3.0 from Fry's electronics. I can't seem to identify the fuse on my board just by looking, and I don't see it in the schematic.

Can someone provide a picture to identify it?

aEx155: I can't seem to identify the fuse on my board just by looking, and I don't see it in the schematic.

Has the obvious answer set in yet?

[quote author=James C4S link=topic=82743.msg621666#msg621666 date=1323640827]

aEx155: I can't seem to identify the fuse on my board just by looking, and I don't see it in the schematic.

Has the obvious answer set in yet? [/quote]

If the case is it doesn't have a fuse, then I don't know why USB power isn't working correctly.

Any ideas?

Either your USB isn't putting out 5V or you are drawing so much current that it is drooping. (A fried chip may be causing the excessive current draw.)

[quote author=James C4S link=topic=82743.msg621725#msg621725 date=1323643264] Either your USB isn't putting out 5V or you are drawing so much current that it is drooping. (A fried chip may be causing the excessive current draw.) [/quote]

Checking with my multimeter I can see 5.2v coming directly from the USB plug, but only 3v on the 5v pin of the Arduino.

Does this help track down the fried chip?

Do you have anything connected to Vin? What about the rest of your circuit?

[quote author=James C4S link=topic=82743.msg621755#msg621755 date=1323644564] Do you have anything connected to Vin? What about the rest of your circuit? [/quote]

The measurement was done with only the USB cable plugged in.

Follow the traces and test it at each testable point to see where it drops. BTW 5.2v is a bit high for USB output. It is not enough to fry anything but usually its between 4.8-5.1v.

smeezekitty:
Follow the traces and test it at each testable point to see where it drops.
BTW 5.2v is a bit high for USB output. It is not enough to fry anything but usually its between 4.8-5.1v.

Wonderful idea, smeezekitty.

Following the EAGLE layout in conjunction with the schematic, I believe I’ve traced the problem to the diode D1 (MBR0520) on the bottom of the board. Temporarily shorting it out with a piece of wire makes the Arduino function correctly when powered by USB. Checking its resistance it reads 414 ohms, which is probably why I was only getting 3v to the regulator. Hopefully I can find a replacement diode at a local electronics shop.

Thanks everyone.