USB ports misbehaving due to PSU

[berniedd]

Just sharing my experience, guys. After we got back from a week's vacation, our trusty 3- year old desktop wouldn't turn on. Simple enough, there was a popped capacitor in the 12-volt line. I replaced the PSU with an older generic 350 watt unit I repaired months earlier with low ESR Samxon caps. Since then, intermittently the USB printer wouldn't print and USB sticks couldn't be read. A reboot usually made it behave.

After I replaced the output caps in the 3.3, 5 and 12 volt lines in the bad 500 watt PSU with the required low ESR types (Samxon brand again), I swapped it back into the desktop and the USB problems all went away. Seems like the older PSU didn't have enough juice. What confuses me is why only the USB ports were affected. The rest of the computer ran like a top.

[joshnz]

Re: USB ports misbehaving due to PSU

USB ports may be using 5vsb for the power. older supples had very little current to supply on the standby rail.

[ratdude747]

Re: USB ports misbehaving due to PSU

Just sharing my experience, guys. After we got back from a week's vacation, our trusty 3- year old desktop wouldn't turn on. Simple enough, there was a popped capacitor in the 12-volt line. I replaced the PSU with an older generic 350 watt unit I repaired months earlier with low ESR Samxon caps. Since then, intermittently the USB printer wouldn't print and USB sticks couldn't be read. A reboot usually made it behave.

After I replaced the output caps in the 3.3, 5 and 12 volt lines in the bad 500 watt PSU with the required low ESR types (Samxon brand again), I swapped it back into the desktop and the USB problems all went away. Seems like the older PSU didn't have enough juice. What confuses me is why only the USB ports were affected. The rest of the computer ran like a top.

FYI- generic no-name PSUs a lot of time need more than caps... things like delta electronics, hipro, ac-bel, seasonic, etc. are ok but others often have cut corners and fraudulent wattage and safety ratings. do you know what brand the 350W unit was?

[severach]

Re: USB ports misbehaving due to PSU

What confuses me is why only the USB ports were affected. The rest of the computer ran like a top.

USB is one of the few places 5v is used directly. PCI I/O uses 3.3v. All the other voltages go through regulators where a little slop on the input won't make any difference.

[berniedd]

Re: USB ports misbehaving due to PSU

FYI- generic no-name PSUs a lot of time need more than caps... things like delta electronics, hipro, ac-bel, seasonic, etc. are ok but others often have cut corners and fraudulent wattage and safety ratings. do you know what brand the 350W unit was?

It's a CPI (no-name generic).