I turn my computer and all the peripherals on/off with a master switch on my surge protector. Flip the switch, the computer boots up, the printer starts, the empeg lights up, so does the scanner, my wireless headphone transmitter, my cell phone charger, the Karma dock, the Panasonic camera battery charger, the charger for my electric razor, my speakers, and a 7-port externally powered USB hub. That surge protector power strip powers 12 different things, although not all of them are actively taking power at any given time (my electric razor, for instance, gets charged every couple of weeks, the cell phone every five or six days, the camera stuff just once in a while, etc.)

The latest addition was the USB hub, and it has caused a strange behavior.

If I flip the master switch with the USB input cable connected to the hub, everything powers up except the computer itself. It just sits there dead, fiddling with the power button on the front of the computer does nothing, nor the main switch on the back.

"Oh, no," I thought. "I've lost a power supply." But... simply unplugging the input cable to the new USB hub instantly starts the computer running, and after it boots up I can plug the cable back into the USB hub and everything works just fine.

This is peculiar behavior, is it not? The only outputs from the hub are a USB cable for an Olympus camera (not connected to the camera; and USB connections to my printer and to the empeg.

I haven't done any systematic trouble-shooting yet (first thing will be to unplug all the output cables from the hub and see what happens) but I am curious to know if anyone has any ideas right off the top that might account for this.

tanstaafl.

I'd guess it's a voltage spike riding back on the USB cable into the PC somehow, as a result of all the crap you've got plugged together. Sort of like a ground loop, only worse. It also might be a "last straw" situation, a red herring that disguises another component in the mess being the true culprit.

Now I have done, and I think I have found out what circumstances produce the problem.

If I leave the 7-port hub unpowered (it has its own wall-wart) I can plug everything* in, flip the switch, and everything works. If I have the hub connected to its power supply when I flip the switch, the computer stays dead.

Is there a limit to how many USB items can be connected? What are the ramifications of running that hub without its external power source connected? It seems to be doing nicely without it, and everything works the same whether it's plugged in or not, except that my computer won't turn on from a cold start when the hub is plugged in.

I just finished sorting through and "neatifying" my cabling, and was appalled at everything I have connected.

*AC Connections:
1) Computer
2) Monitor
3) Printer
4) Scanner
5) USB External HD
6) Speakers
7) empeg
8) Karma
9) Wireless headphone transmitter
10) Charger for Panasonic camera battery
11) Charger for Olympus camera battery
12) Charger for cell phone
13) Charger for razor
14) Charger for bicycle light
16) Second surge-protected power strip
16) [Power supply for 7-port USB hub]

USB Connections
1) 7-port USB Hub
2) Mouse
3) Printer
4) Scanner
5) USB hard drive
6) empeg
7) Karma
8) Panasonic camera
9) Olympus camera
10) Card reader

Now I'm feeling unfulfilled... I still have three USB ports and four AC outlets with nothing in them.

tanstaafl.

Does your USB hub have a switch for when you've got the PSU plugged in?

No. All I can do is plug/unplug the power connector.

tanstaafl.

If the devices plugged into the hub function without the psu, then you might not need it. You might not be able to use the USB-charging feature of your devices, but you might not own any devices that have that feature.

None of the things that plug into the hub contain batteries that recharge through the USB port: Karma, Panasonic Camera, Olympus Camera. They all have their own recharging systems.

tanstaafl.

Some PCs connect the USB power to the 5V standby output of the power supply when the PC is off so you can do wake on keyboard. If your hub isn't designed correctly and feeds power back to the PC when its self powered then your PC may act oddly.

More weirdness.

I replaced the hub that kept the PC from booting with another one. That one allows the PC to boot even when the hub's power supply is connected. However, my mouse won't worked when plugged into that hub. Everything else works, but my mouse won't. If I plug the mouse into one of the USB ports on the computer itself, then it works, but it won't work when plugged into the hub, even if it is the only USB device plugged in.

On a whim I daisy-chained the old hub onto the new one, plugged the mouse into the old hub and it still wouldn't work.

???

tanstaafl.