USB over-current wtf?

[Terranova]

I'm trying to help my friend out with his computer. Seems to boot up fine no mobo errors the only thing that's wrong is we keep getting this "Warning, USB Over-Current! Shutting down in 15 seconds! I've tried disabling the USB hubs. I've unplugged EVERYTHING (hard drive, cd-drive, ram, everything that would still allow it to run without) checked to make sure the mobo wasnt shorting out touching the case. Tried it outside of the case, removed the bios battery for an hour. Reset the BIOS to default. We've basically done everything we can think of. I contemplated a BIOS update but I don't know if that will make a difference. What are your thoughts? Oh ya it's a Foxconn AM2+ A7GM-S paired with AMD Athlon(tm) 64 X2 Dual Core Processor 3800+, MMX, 3DNow (2 CPUs), ~2.6GHz 2 gigs of RAM HD3850 SB Audigy 2 ZS Windows XP Professional (5.1, Build 2600) Service Pack 3 (2600.xpsp.080413-2111)

 

[cyberfish]

Sounds like there is a short on one of the USB ports for some reason. IIRC, the outer 2 leads of a USB port supply power (5V and gnd). Make sure they are not connected anywhere, including on the motherboard (the pins).

 

[redduc900]

There's 3 USBPWR jumpers on that board (USBPWR1, USBPWR2, and USBPWR3), the first located adjacent to the front panel connectors, the second next to the S/PDIF OUT connector, and the third directly above the battery. Make sure the jumpers are installed on all three sets of PWR pins in their default locations. Pins 1-2 are default +5V, and pins 2-3 are +5VSB. If any of the jumpers are on pins 2-3, then Power Management Setup--> Resume by USB Devices needs to be set to Enabled in the BIOS.

 

[Terranova]

There are no USB jumpers on the board accept for 2 right next to the battery and I think one is for CMOS reset and the other is chassis. There are no Other jumpers anywhere on the board.

 

[bldegle2]

yeah, that board is severely lacking in jumpers, I checked the manual....i would have to conclude there is a problem with the MB proper, something is shorted causing the over volt....

just for kicks and giggles, cruise into the bios and check the PS voltages (12v,5v,3.3v), especially the 5 v line.....if the PS has gone wacko it may be sending an overvolt to the 5v line....

I am betting bad MB or shorted connector....

good luck....

laterzzzzz...................

 

[cyberfish]

The voltage probably has nothing to do with it. If there is no load (open circuit), no matter how high the voltage is (till a few thousand volts, the dielectric strength of air, beyond which air becomes conducting), there will be 0 current.

If you read the voltage in BIOS, it should actually be LOWER than 5V if there is a short circuit, because the filters (capacitors) on the 5V line will be discharged too much (voltage drops below the reference voltage) in each cycle of the rectified AC input, and there will be a bad ripple.

 

[Trap05]

I've seen this exact message before and it was due to a physically damaged USB port on the boards back panel. Inspect the ports for damage.

 

[cyberfish]

If you have a multimeter, turn the computer off, set the multimeter to ohm-meter mode, and put the probes to the 2 outer leads of all USB ports (5V to ground). If it says ~0 ohms (or significantly lower than other ports) for one of the ports, you know you have a short circuit there.

 

[QuietIce]

If you have a multimeter, turn the computer off, set the multimeter to ohm-meter mode, and put the probes to the 2 outer leads of all USB ports (5V to ground). If it says ~0 ohms (or significantly lower than other ports) for one of the ports, you know you have a short circuit there.

+1



A 3 VDC flashlight and a couple of pieces of wire would work as well if a MM isn't available ...

 

[cyberfish]

There is a potential problem with both methods, though (flashlight and multimeter). If the power supply has low resistance even when it's off (some are, if you run the current the right way through the diodes/transistors), you can't be sure if it's a short.

A more reliable but a lot more difficult way is to connect a resistor from 5V to gnd, and use an ammeter to measure the current through the resistor when the computer is turned on. If there is no current, that means there is a short, since the short provides a ~0 resistance path, and all current will flow that way. I suppose you can check the voltage, too. It should say 0V if there is a short (when the computer is on).

 

[QuietIce]

I wouldn't use the flashlight method with the PSU plugged into the board anywhere. Or were you talking about the power control chips on the board ...?

 

[cyberfish]

I don't know how PC power supplies are made, but I wouldn't be surprised if the USB 5V is connected directly to 5V from the power supply. Nothing wrong with that.

To the USB port, the motherboard is a power supply. It doesn't matter how the power is routed on the motherboard side, as long as it can make a potential difference of 5V when it's on.