Plugging in HDMI fried motherboard with PicoPSU

[dthorne]

I'm in the process of building a mini-itx HTPC that I am going to put in an old NES. I was trying to fire up the motherboard to test if the system worked and to start installing some software while I finished up the case.

I plugged in the picoPSU that I bought and the power brick. I rigged a switch to power on the board and the fan started spinning on the heatsink. Everything seemed fine. I plugged an HDMI cable into my monitor that is attached to my desktop and when I plugged it into the new motherboard there was a huge arc that obviously fried the MB. I'm not sure what caused this shock but I want to make sure it doesn't happen again. What would cause this? Does the picoPSU need to be grounded? I'm terrified now to plug anything into the MB because I don't want to fry it. What can I do about this?

 

[DarkSable]

If the PSU was plugged in, then it WAS grounded. You probably already fried your motherboard, which is the downside of things.

If you have another computer, I'd use it (Plugged in, not turned on) to ground yourself every coupla seconds. Just touch any BARE metal.

 

[dthorne]

I already have a replacement MB on the way, I just want to make sure it doesn't happen. I have a static wrist strap that I can where when I am assembling the next MB. My worry is that when it is all done, each time I plug in the HDMI cable how do I know it won't arc like that and cause some serious damage. The shock seemed much bigger than a static shock. It made a pretty large arc and snap. Do I have to ground myself every time I want to unplug any sort of connection to the PC?

 

[chugot9218]

Did you happen to see where it arc'd? Sounds like a MOBO short, I don't think a shock from static would look as dramatic as you have described, but I could be wrong.

 

[dthorne]

As I was plugging the HDMI in. It arc'd from the HDMI cable to the port on the MB. It left a pretty decent scorch mark on the outside of the port on the MB.

 

[chugot9218]

Hmm, to me that sounds like there was current coming to the actual port, which would be a big problem but I am thinking it would be on the manufacturing end. Did you RMA the board instead of simply buying a replacement? I am not really an huge expert in all of these fields I am somewhat, but am pretty good at deduction, so take a lot of my comments at face value, and hopefully someone with a little more electrical experience can elaborate.

 

[dthorne]

Yeah, I RMA'd through Newegg. They are super good about it.

 

[chugot9218]

Cool good to hear, it sounds like a defect on the board, I don't think you screwed anything up. It sounds like you probably did, but on your next attempt, I would make sure nothing is plugged into the other end of that HDMI lol.

 

[weaselman]

As a point you in fact have two grounding points on a connector one for the connection pins interface, and the outer sheild or hold metal surround should also be grounded.
It may be a case that the Hdmi cable was not double grounded, most likely no ground to the outer connection sheild.
That would explain why it worked ok. And when it came to connection of the Hdmi cable it popped the board.
Was it a cheap Hdmi Cable ?
You may consider buying a better quality cable if the case.
Anyway I guess when you get the new board it may be best to connect it up first to both ends before power up of the system, or the Tv just in case.
Best of Luck.
Shaun.

 

[dthorne]

Thanks for the help, friends. The cable is in fact a a very cheap one. It came free with the MB. I have the PicoPSUs external connector mounted in a small piece of sheet metal that holds it in the back of the case. The metal connector is in direct contact with that sheet. I wonder if this is part of the problem. However, the sheet metal isn't in contact with anything else and it was sitting in the plastic case at the time. If I wired one of the bolts I have holding the MB to the outer connection shield would that make a difference? Because right now the sheet that the outer shield is connected to and the metal the MB is mounted to are not connected.

 

[weaselman]

All Psu`s should be grounded, Pico or ful sized PSU`s. Again two types of grounding.Each electrical power feed from the Psu to the mother board power connectors is grounded Ie: 12v+/12v ground 5v+/5v ground. 3.3+v/ 3.3 ground. and the chassis should also be grounded
with the Psu in contact of the metal plate inside the case where the mother board is mounted.
so when you get a short it reduces the chance of damage to components of the board, instead returning to the ground of the wall socket.

I think it may explain it for you is the PSU grounded to the chassis plate?. If not the case, then as I said next time plug the cable into both ends before any kind of power up of the pc or tv. Then power it up, or make sure the outer Psu case is grounding to the mother board mounting plate as well.That is why when your building a Pc a anti static wrist band is always crocodile cliped to the metal chassis as it contains a ground if wired right to stop static from your body damaging the sensitive components of the board during any kind of human handeling before it is attatch to the grounded back plate of the chassis of the case.

 

[noob2222]

id make sure to check around the hdmi port next time with a volt meter, see if there is anything around the baseplate.