Do not do this...burn your ATMEGA16U2

Remember kids. If you have a faulty power supply (aka. tazing you if you touch the GND/USB connector shielding), for either the arduino or some external peripheral stuff...do NOT use it.

Because i did.

While the external (faulty) power supply was connected to a p-channel fet, i plugged in the usb cable. Right after that my PC dropped dead.
After a short time and some inspection the PC did turn on, and everything seemed to work fine, even the USB ports.
But when i wanted to connect my arduino UNO, it was not recognised by the system. Tried on different computers...same story. The ATMEGA328 however seems to work just fine. But the board is stranded as of right now.

On second thought, i might use my other board's Tx/Rx pins to bypass the usb interface. However i'm worried if there's a short somewhere, i might burn my other remaining board.

What say you? :slight_smile:

PS. If i remember correctly bot the Tx/Rx lines from the usb chip have 1k resistors on. So i'm guessing even if there's a short on the chip, i probably wouldn't amount to anything serious.

Put it aside.

When you have a USBASP (cheap on eBay) or a second Arduino to work with, you can try and re-flash the 16U2 via its ICSP header.

To be honest, i'm quite sceptical...since i strongly believe the chip is fried. I've took a look at it and noticed that at the left center, 4 label characters have turned from the normal gray-green color to black.

The PSU i connected is leaking 80V AC from mains. In the past i noticed that the arduino usb connector shielding(ground) was at 80V. When i connected to the PC i suspect this voltage somehow ended up trough the chip.

I did order a FTDI adapter though. So i'm not throwing it away at least. :slight_smile:

I'll get over a dead USB chip, but i did panic when my PC dropped dead and wouldn't turn on. That was terrifying. :sweat_smile:

What kind of PSU do you use? Is it a switching type? Does it have a mains earth pin? Is it connected to mains earth?

Most switching PSU's (computer PSU etc) have some caps to mains earth and if mains earth isn't connected but you connect it to something that has mains earth (PC for example) the ischarge can indeed fry chips :wink:

It is a farily decent ATX PSU. However in the past i might have overpower it. Then it started to zap me with 80V AC trough every line and the housing if i was touching earth ground.

I've tried swaping the ATMEGA328 from my broken board to a new board, but the Tx/Rx port does not work. It gives me a out of sync or something message.
I've then tried to use the good board's ftdi to program the damaged board...and still nothing.
After that i've tried to program it trough ISP and still nothing.

I have a couple of questions tough. If using Arduino as ISP, do i need to put a cap on the reset-ground pin in order to prevent it reseting? All the images do not show a cap, but when doing the attiny you need one. I'm just guessing.
Should i reburn the bootloader on the damaged one?

Should i cut the Tx/Rx line from the Atmega16u?
I'll try and check if the TxRx are high in the meantime.

far_1:
If you have a faulty power supply (aka. tazing you if you touch the GND/USB connector shielding), for either the arduino or some external peripheral stuff...do NOT use it.

far_1:
It is a farily decent ATX PSU. However in the past i might have overpower it. Then it started to zap me with 80V AC trough every line and the housing if i was touching earth ground.

Should i cut the Tx/Rx line from the Atmega16u?
I'll try and check if the TxRx are high in the meantime.

So you continue using this power supply / AC arrangement?
I think that tx/rx/arduino_as_isp/etc. are the least of your worries - you're re-arranging the deck chairs on the Titanic before having another go at that iceberg.

No, i'll never use this PSU again...at least not for delicate stuff. Take note that the PSU was not powering the arduino but was connected to a p-channel mosfet. How did it break trough, i'm not sure.

My goal now is to try and salvage what's left of the broken board.

As described, that PSU is a known hazard that you used anyway.

Would you like to warn me about jumping off cliffs?

RIP. Arduino Uno #2, 2014-2015. May you suffer no more.

Diagnosis:
Found the Rx line was not high, even if i forced it high. Probably a short in the A16U2. Took out the a328 to confirm. Rx still not high. Then i noticed over heating of a SMD resistor. Burning hot. Decided to de-solder the A16U2 with a heat gun. Turned on again...resistor still insanely hot. Reinserted the a328. Chip wont reset.
Declared dead at 00:30.

Post op.:
Retrieve crystal and a328. Attempt to reconstruct barebone setup.

It was insanely stupid of me to use the PSU even though i knew it was faulty, but it was right in front of me. So tempting.

far_1:
It is a farily decent ATX PSU. However in the past i might have overpower it. Then it started to zap me with 80V AC trough every line and the housing if i was touching earth ground.

So I'll ask again, is the PSU connected to mains earth?

Sounds like it's not. And then it can be a perfectly fine PSU but all ATX PSU without mains earth connected will have a voltage between mains earth and the lines and will zap you!

You cannot ride a dead horse.

Oh, instead of just using 6 words, I could have made tons of technical statements.

However, I cannot beat Dakota tribal wisdom.

I do know that this kind of NON-TECHNICAL statement should NOT be in a TECHNICAL forum. But in this case the Indian´s answer was better then many other answers.

And I just saw it .... (see above)

someone else seems to share my idea. He talks about "deckchairs and icebergs". Same story - different words.

Once you've established that the horse is in fact dead and convinced the OP of the fact, which I'm not so sure has been done.

I'd have that PSU apart and everything useful salvaged starting with the power cables and fan, but I know how to not get shocked or burned and I'm not sure that the OP wouldn't say "wth" and just plunge in. But then I know why electricians insurance is required, how easy it is to get gangrene from a short running through a body part.

Also I don't think that Native Americans have a lock on statements about the bleeding obvious.

Hehe. Was hoping for some humor :slight_smile:

Anyway…the PSU is a LITEON, which is a recognizable brand in the PC market. Worked perfectly until that one session. Still does output a stable voltage on every line, with the added bonus of having a 80V AC component.
The PSU has a earth ground connection (i believe trough a R+C line), but obviously something is wrong.

Peculiarly, i did once a long time ago had a wall wart adapter that had the same issue. It was outputting some mains voltage to the arduino USB case (i opened a thread once about it). At that time i was still a total noob and kept working as usual. Plugged it into the PC without any problems.

I guess my subconsciousness told me to go ahead. I’m sure if i had a diode in series nothing would have happened, since the mosfet was rated for 200V, and would easily handle 80V.

But like i’ve said. The PSU is out now.

I’m only sad that now i have laying around a pretty arduino board.