5V gives 3.5V is board broken? :(

Good day!

I've tried to measure voltage on 5V pin of my Arduino -- it is 3.5V, on the 3.3V pin it is 3.3V, so my multimeter seems to work.

Is my board broken? :(

I CAN upload sketches, blink leds on any digital pin etc.

I tried to power from external supply with 12V and it gives me 5V!

I tried to power from external supply with 12V

And how was it powered before?

From USB, is this not enough for it?

This page http://arduino.cc/en/Main/ArduinoBoardDuemilanove

The Arduino Duemilanove can be powered via the USB connection or with an external power supply. The power source is selected automatically.

Is this a error and it always need external supply to work realible. Or my board is broken?

This leads to problems with LCD display, that were resolved with great help of floresta: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1287745515/0

If its 3.5v from USB its a function of the USB, not the board. Have you tried a) another USB lead, b) another computer ?

Compare the voltage on vin and the 5v pin, when powered by USB.

Here are the results:

  • With my notebook and original USB cable -- still ~3.5V on +5V almost the same value on Vin.

  • I've tried with the same result:

  • Different USB cable to the same notebook

  • Different and original USB cable to other notebook

  • Different and original USB cable to USB charger (which I use for other my USB gadgets)

When powered with external +9V, the +5V gives straight +5V, Vin around 9.5V.

You should measure the actual voltage coming in via your USB cable. On my Duemilanove there are four pins on the bottom of the board, under the USB connector. With the board upside down and oriented so the USB connector is at the top then the upper right pin is GND and the one directly below it is the VCC pin. I get 4.93 volts from my desktop and 4.99 volts from my netbook.

Don

There are about a dozen unknowns here. It is possible that your Duemilanove(?) board is broken, but it doesn't seem very likely.

Thank you for the response, here are detailed report:

Board: Duemilanove, brand new from e-bay Connections to board: none, board is loaded with "Blink" example (http://arduino.cc/en/Tutorial/Blink) Measurements: Voltage is measured by multimeter on +5V pin and GND (all on the header which is on the bottom of the board if you take it as on this picture: http://arduino.cc/en/) Power connections: - USB from my notebook with stock cable - USB from other notebook with stock cable - USB from USB charger - USB from my notebook with my printer cable - USB from other notebook with my printer cable - USB from USB charger with my printer cable

Voltage is about 3.75V. When I connect board with external +9V using power socket I get +5V.

Please let me know if I missed any details.

Voltage is about 3.75V. When I connect board with external +9V using power socket I get +5V.

When you connect the external power supply the FET turns the USB supply off. When you disconnect the external supply the FET turns the USB supply back on. The 'path' is then as follows: USB connector --> Fuse --> FET --> +5V pin

In order to tell if there is something wrong with your board we have to know what voltage is present at the USB connector. If it is ~5v then you have a problem with the Fuse or FET. If it is ~3.75v then you have a problem with your USB source(s).

Board: Duemilanove, brand new from e-bay

Yours may not be a 'real' Duemilanove. On mine the words Arduino and Duemilanove are center justified and on yours they are left justified, but that may not be a definitive way of determining the authenticity.

Don

A Duemilanove from Ebay is practically guaranteed to be fake. Having said that I have a fake that works identically to my real ones, it shouldn’t make much odds.

A Duemilanove from Ebay is practically guaranteed to be fake. Having said that I have a fake that works identically to my real ones, it shouldn't make much odds.

Yes, my definitely is not a real Arduino, I'd like to call it "clone" :)

When you connect the external power supply the FET turns the USB supply off. When you disconnect the external supply the FET turns the USB supply back on. The 'path' is then as follows: USB connector --> Fuse --> FET --> +5V pin

I've measured voltage on USB pins as you described above (on the back of the board). It gives 5V, so it seems that something is wrong in the board.

Thank you for this description: http://web.alfredstate.edu/weimandn/misc/Arduino%20Duemilanove%20Power.gif

It seems that FET you mentioned is T1 NT2955, and fuse is F1 (I used this schematics: http://arduino.cc/en/uploads/Main/arduino-duemilanove-schematic.pdf).

Here is a photo with elements:

Have I identified them correctly? How can I check which one is broken?

They both are SMD and in addition transistor is FET (hard to solder by hand?), so they seems hard to replace?

P.S. I'm not sure, but it seems I have one time where fuse was turning board off, but it should return to normal state after diconnecting?

According to schematics, fuse is on +5V line, can I try to measure voltage on one side and on another of the fuse?

Have I identified them correctly?

Yes.

How can I check which one is broken?

See below.

They both are SMD and in addition transistor is FET (hard to solder by hand?), so they seems hard to replace?

They are too small for my eyes and fingers to deal with.

P.S. I’m not sure, but it seems I have one time where fuse was turning board off, but it should return to normal state after diconnecting?

In this case I would say that there is a good possibility that the fuse is the culprit.

Measure the voltage between GND and each end of the fuse. The voltages should be essentially the same. If one is ~5v and the other is ~3.7v then the fuse has not fully recovered from whatever you did to it.

If the fuse is OK then check out the FET. You want to compare the ‘source’ voltage (the upper right pin in your photo) with the ‘drain’ voltage (the left or center right pin). If these two are not the same there could be a problem with either the FET or the Op-Amp (the 8-pin IC just to the left of the 328).

Don.

Don, thank you for helping me out so much!

I've checked fuse -- it gives me 5V on both sides. FET:

pin on the left side - 5V

pins on the right (as on the picture): - 3.57 - 5V - 2.5V

I have some friends, that can replace such small components for me, so I just want ot find the faulty one.

Just to toss in my 2 cents, I've got an ebay arduino and the regulation of external power does not work correctly. Connect a 9v battery and the board 5v goes to 7.5v, higher when connecing to 12v.

@zoomkat:

Just to toss in my 2 cents, I've got an ebay arduino and the regulation of external power does not work correctly. Connect a 9v battery and the board 5v goes to 7.5v, higher when connecing to 12v.

His problem is just the reverse, the regulator circuit is working but the USB supply is not.

@artvolk: The gate voltage (the 2.5 v on the bottom pin) seems wrong. The output of the comparator should be ~0v with no external supply connected and the noninverting voltage follower shouldn't change this (mine gives ~2.5mV). Perhaps the comparator is oscillating - or maybe someone else has another idea.

Don

Just to toss in my 2 cents, I've got an ebay arduino and the regulation of external power does not work correctly. Connect a 9v battery and the board 5v goes to 7.5v, higher when connecing to 12v.

Yes, the problem is opposite: from USB it gives me 3.5V enough for MCU to work (so I even not noticed this playing with LEDs etc), but this is too low for 16x2 LCD, for example.

@artvolk: The gate voltage (the 2.5 v on the bottom pin) seems wrong. The output of the comparator should be ~0v with no external supply connected and the noninverting voltage follower shouldn't change this (mine gives ~2.5mV). Perhaps the comparator is oscillating - or maybe someone else has another idea.

What is your estimate, can I use it with external supply in the future without repairing (returning it to the seller will cost more than new one :))?

What is your estimate, can I use it with external supply in the future without repairing (returning it to the seller will cost more than new one )?

That's what I would do.

You could try to find someone with an oscilloscope who could check out the comparator. If that is the problem it might be tamed with a capacitor or two. Maybe Grumpy_Mike will chime in with his opinion.

Don