Lesh
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Circuit burnout issue

Sat Jun 22, 2013 11:00 am

Hi,
I'm a newbee. I've just powered up my RP for the first time using my mobile phone charger, which worked. But within seconds I saw smoke coming out and found part of a circuit just under the power supply connection on the RP had burned out. I had the RP on the carpet, so the circuit had stuck to it and came off the RP. This may teach me to be more careful, but I want to know if it was just because it was on the carpet or because the power supply-mobile charger wasn't suitable - overpowered. Or was I just unlucky to have a duff RP! I'm no expert so will give all the details on the plug:
Nokia charger - AC-10X
Input: AC100-240V/ 50-80hZ/ 160 mA
Output: DC5.0V/ 1200mA
I understand that the RP requires at least 1000mA (1A) output, so 1200mA would seem ok!
Any thoughts/advice (other than being more careful with it when I get a new one) appreciated. Thanks

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elektrknight
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Re: Circuit burnout issue

Sat Jun 22, 2013 2:49 pm

Yikes!
Sounds pretty scary. The AC-10X Nokia charger has been discussed in this thread so it should have been OK.
http://www.raspberrypi.org/phpBB3/viewt ... f=2&t=5105

What kind of carpet do you have? Any chance it is conducting?

To diagnose the problem it would be good to know which part of the circuit came off the board.
When you look on the bottom side of the PCB there are white labels identifying the components,
try looking for the missing one and read the label closest to the PCB pads.
Placek Malinowy to jest to!

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Burngate
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Re: Circuit burnout issue

Sat Jun 22, 2013 3:46 pm

Under the power connector is only F3 - the poly-fuse - and D17 - the over-voltage protection diode, either of which could get hot in a fault condition, but which should stay cool enough to touch under normal conditions.
I've no idea how hot carpets need to get to melt - boiling coffee doesn't, but soldering irons do.

Can you post a picture of the offending item? (The Pi, not the carpet!)

samson241
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Re: Circuit burnout issue

Sat Jun 22, 2013 4:43 pm

Burngate wrote: I've no idea how hot carpets need to get to melt - boiling coffee doesn't, but soldering irons do.
(
I don't think that 5 volts could do that and i wasn't under the impression that the Rpi had an amplifier or a transformer on the board. It is time to start considering a crap charger(test with device it is meant for to be sure) or a faulty Pi...
I realize this question must seem stupid and i apologize in advance.

Lesh
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Joined: Sat Jun 22, 2013 10:45 am

Re: Circuit burnout issue

Sat Jun 22, 2013 4:54 pm

Thanks guys,

I've attached a photo - the burnt off component is next to about where it came off. Because it's a clean burn off I'm not sure if it's the D17 or F3 component.

I should have added that as well as powering up the RP with the Nokia charger I tried an old powered USB hub - Saitek - at the same time, but doubt that would have made any difference. On a side note as this was for the original USB (1) would this still work with any newer USB (2) devices plugged into it?

As for the Nokia charger itself I've used it for ages to charge my mobile so it should be fine.

Cheers
Attachments
RP component burn out.jpg
RP Burn out photo
RP component burn out.jpg (46.63 KiB) Viewed 3353 times

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elektrknight
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Re: Circuit burnout issue

Sat Jun 22, 2013 5:08 pm

It is D17 transient-voltage-suppression diode.

Looks like you had either bad D17 part that activated with a 5V or your power supply is
bad and is outputting way more then 5V.

Well, your Pi might still be OK, check this thread on D17 replacement.
http://www.raspberrypi.org/phpBB3/viewt ... 5&p=370751

At this point you could try using another good known power supply that is rated 500mA.
Last edited by elektrknight on Sat Jun 22, 2013 5:15 pm, edited 1 time in total.
Placek Malinowy to jest to!

odysseus55
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Re: Circuit burnout issue

Sat Jun 22, 2013 5:10 pm

I agree it is definitely D17.

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Burngate
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Re: Circuit burnout issue

Sat Jun 22, 2013 5:29 pm

Yes, D17.
It's a bit like - well, very like - a zener diode. Up to about 6v it does nothing, but above that it starts conducting, and should take enough current to blow the poly-fuse - the green thing beside it.
If the poly-fuse doesn't blow, it'll get warm enough to destroy itself - or unsolder itself, as yours has done.

Now the fact that the poly-fuse didn't appear to work, and that you mention an old powered hub, makes me suspicious.
If that hub is back-powering the Pi, and is putting out more than 6v, the poly-fuse won't protect the Pi. But if this is what happened, you may be lucky - D17 may have done its job.

I would be getting a meter and measuring what's coming back from the old hub.
And also measure if you can what's coming out of your charger, before plugging it in to the Pi again

klricks
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Re: Circuit burnout issue

Sat Jun 22, 2013 5:40 pm

Either the Nokia supply or the supply on your USB HUB is broken and outputting more than 6V. You should test both supplies before trying to power the RPi again. Past experience does not guaranty something is still working.

Many USB hubs will backfeed power to the RPi even though they are not supposed to do that as many hub makers do not follow the specifications. If so both power supplies would be attempting to power the RPi at the same time. Not good but not necessarily the cause of your problem.
Read up on backfeeding..... many threads here.

If there is not other damage then the RPi will work without the D17, but there would be no over voltage protection. So a future mishap would likely destroy the RPi.

Fuse F3 looks to be intact but if it was tripped it could take quite some time to come back to normal. Many hours to days.

You should really have a case or some kind of protection for the RPi board. A stand of wire or other conductive material can short out circuits...... Especially vulnerable are the GPIO pins.

Also static electricity can weaken or destroy parts on the board. You should use the same care as you would with any other electronic device with exposed circuits.... Computer cards, memory, motherboards etc.
Last edited by klricks on Sat Jun 22, 2013 7:06 pm, edited 2 times in total.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

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johnbeetem
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Re: Circuit burnout issue

Sat Jun 22, 2013 6:07 pm

Since D17 desoldered itself, it's most likely that it was conducting a large current from a power supply greater than 5V, as others have suggested upstream.

Putting an electronic device directly on a carpet is a bad idea.

1. You could easily have a bit of conductive material in the carpet, which could short something out.

2. Carpets are good thermal insulators, and RasPi's back side gets very warm, especially the rev 1.0 board. I found mine got hot sitting on an anti-static bag, so it would be much worse on a carpet. I've heard of laptops overheating sitting on a carpet, particularly if the air vents are blocked. However, it's unlikely to make things hot enough to desolder a component. (But it's a good way to boil electrolytic capacitors -- I had that happen to an ADSL modem sitting on a carpet in a case. Lousy thermal design on that modem.)

My RasPi rev 1.0 is vertically mounted so that it gets passive air flow on both sides of the PCB.

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Jim Manley
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Re: Circuit burnout issue

Sat Jun 22, 2013 7:34 pm

John - this looks like the scenario we postulated a few months ago with a lapdock going rogue - a Supply's Gone Wild video is the result! :) Pretty amazing that D17 managed to desolder itself as that means the joints got North of 650 degrees F. That also means it went out-of-circuit and was therefore no longer providing over-voltage protection for some amount of time until the power was cut.

It's possible the phone charger does, indeed, supply 5.0 volts at 1200 ma, but its open-circuit voltage could be upwards of 6 volts or more, perhaps due to high internal resistance. If that's the case and the Pi is only drawing a few hundred ma due to the powered hub taking the load for peripherals, the semi-loaded phone charger could easily have been delivering closer to 6 volts, or more. A similar situation could have been occurring for the USB hub's power supply, and in the worst case where both supplies may have been delivering significant over-voltage, well, D17's days would have been numbered in any case.

I would look for something like a staple on the carpet that could have caused a short - all of the typical carpet materials should be insulators. Static wouldn't be a factor in this case, unless a discharge caused a semiconductor power component to go stupid at just the wrong time. A short shouldn't have resulted in D17 trying to commit suicide though, that still points to an over-voltage situation.
The best things in life aren't things ... but, a Pi comes pretty darned close! :D
"Education is not the filling of a pail, but the lighting of a fire." -- W.B. Yeats
In theory, theory & practice are the same - in practice, they aren't!!!

Lesh
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Re: Circuit burnout issue

Sun Jun 23, 2013 9:46 am

Thanks all, lots for me to think about and look into. The powered hub plug gives 16VDC output, so if it did surge the RP then guess that could have been the cause. I will follow through on the threads provided and let you know how I get on. Ive yet to get an SD card and other items so will be able to say how it's working, or not, a bit later. Cheers

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