I've posted this a couple of times on different forums during the last years but replies are few and nothing has solved my issue, so this time i'm trying TomsHardware instead
For a long time i've had a very annoying problem with my homebuilt system regarding USB.
For example, I can use my USB mouse and an external harddrive at the same time, but if i power on a second external harddrive, attach a flashmemory, printer or whatever that runs through USB, then one or both units stop working (the mouse always works).
So, excluding the mouse, i can only use 1 USB device which means i can never print anything when my external HD is connected, also i can't transfer files from 1 external HD to another. I should mention that all USB devices except the mouse (ofcourse) have separate power supplies.
It's a quite old P4 2.4Ghz, 1Gb with Asus P4PE motherboard with 6 USB ports (might be that 2 of them is 1.1 and the rest is 2.0, can't remember exactly) which i built around 2003. Latest available BIOS is installed.
This sounds very much like a power (current) problem. Two things to consider are upstream and downstream. Upstream is the port where the power comes from, and downstream ports are where you connect such devices as mouse, printer, keyboard, etc.
The reason for your inability to use your printer and external HDDs is simple; overload. Similar to your CPU, a lot of circuitry is designed with a built-in protection to shut down before amp/volt overload fries the circuit.
When you take into consideration how much amperage is actually used by your HDD and printer, you'll see that it is actually not uncommon for USB hubs to automatically reduce their load to prevent permanent damage.
Ok. I think i understand what you mean. In Wiki they talk about 100 mA per USB port and that a max of 500 mA can be transmitted per port (atleast per physical port on the MB). If connecting an USB hub that is not self-powered you then can have no more than 4 devices connected to it (while the hub itself draws 100 mA) which sums up to 500 mA.
However, if my computer have 6 USB ports, why can't it power more than 2 devices? Maybe all units need that 100 mA even though they are self-powered, but that only sum up to 200 mA.
I hope you understand me even though i'm not natively english-speaking
Yes. I understand you just fine. Your english is better than some 'natives'.
As for your theory, you do understand it, but to answer your question you need to find out how much current is drawn by your printer, HDDs, respectively.
Because the motherboard has 6 ports, it is safe to occupy all 6, as long as you don't exceed the limit of what that internal hub can handle -- this is called 'load'. A crude example would be that cup holder McDonald's gives you when you order more than one drink. Said cup holder can handle a 'load' of four McDonald's cups (regardles of size/capacity); anything more than that and the cup holder becomes inefficient.
In short, find out what the current draw is from the connected devices. Once you know for certain of the current draw, you can figure out if either there is too much current demand when all devices are powered up, or if there is a defect with the internal USB hub.
Without checking the "draw" from my USB units, my guess is that something is wrong with the machine (or the internal USB hub like you refer to) as it can't even handle 2 USB flash devices at the same time. They can't really release a MB like that as i have 4 flash memories, 4 external HD's plus other devices, and whatever combination i do, it's always the same, 1 unit tops (excluding the mouse).
I will however try to find more info about what each unit demands in mA. It would be interesting to know.
i've followed up on your problem, what are you system specs?
The other problem aside from PSU load maybe due to the fact that your rig is dieing on you...sinec i had the similar issue with my gigabyte 865PE back in 2004, usb devices failed if i plugged too many in. Al my USB ports were certified v2.0 USB.