0

I have this Chinese (important) LED sign that can be connected to a computer or it can automatically read the information (what text to show) from USB flash drive right after connecting it. It also has a power cord.

Since I have a computer far away from the LED sign I made a USB cable by using 2 USB connectors and 15m UTP cable as I read it is supposed to work. I even tested 2 flash drives and a gamepad and all devices worked properly.

Right after I connected the LED sign to the computer (using my cable) the sign showed some error in Chinese and the computer stopped working. Just black screen, as if I had unplugged the power. And that was it - no smoke, no smell, but it doesn't start anymore.

I tested the PSU on another computer and it is working just fine. Is it possible that I fried my mainboard? I mean, it's USB cable how the hell could that happen? I do not have any mainboard that I can test or borrow from somebody, so can it be something else? I have double (more like quadruple) checked all the connections, I have tried unplugging all devices and plugging them one by one. Nothing.

6
  • Was it the first time you plugged in the sign? It could have been either an electrical fault in the sign or you could have electrocuted your PC with static electricity by accidentally touching the metal casing on the USB plug while it was connected to the PC. I've had my PC restart a few times because of a static shock.
    – positivew
    Jan 14, 2014 at 21:14
  • is it only the screen that's blank or does the laptop just won't do anything (no fan, no light, nothing)?
    – Rodolfo
    Jan 14, 2014 at 21:34
  • @positivew, it was the first time I connected the sign to a computer. I have another sign, but I am too afraid to test it as it can another PC. I was holding the metal casing as I have yet to make a housing, but I doubt that this could fry the motherboard.
    – A Petrov
    Jan 14, 2014 at 22:01
  • 1
    If you have some experience in electronics (or have a friend who does), you could turn on the sign (plug in the power cord only) and test the USB pins with a voltmeter to see if the sign is leaking voltage from its power supply (since it's externally powered) to USB. That could very well fry your motherboard. Usually it would be the PSU, that dies, though. Another suggestion that I found for a similar case is to try and reset you CMOS (BIOS settings). Usually by removing the CMOS battery for a couple of minutes and shorting a jumper, but check your motherboard's manual to be sure.
    – positivew
    Jan 15, 2014 at 9:24
  • 1
    This type of improvised USB extension is catastrophically unsuitable for externally powered USB devices! You need to use an isolator. You can't connect random grounds together with long, thin cable. That can cause fires, damage equipment, and so on. Jan 21, 2014 at 17:27

1 Answer 1

0

I sent the computer for repair. Apparently I was right - the motherboard was fried.

2
  • This sounds like a ground loop. Were both the sign and the compute plugged into the same electrical circuit? Were both circuits grounded? Jan 21, 2014 at 17:21
  • Yes, it was he same electrical circuit. I can not tell for sure if both circuits were grounded. I think it might have to do with the cable being USB AM-AM
    – A Petrov
    Jan 21, 2014 at 18:00

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .