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Old 11-08-2011, 10:09 AM
Pinball Wizard Pinball Wizard is offline
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Join Date: Jan 2011
Location: Silver Spring, Maryland USA
Posts: 181
Default Re: MBox 3 Lights flashing

Auigster: I am very happy that your mbox is now working. Mine is working too but I still am not sure that I understand what happened. I would like to make some real progress on this issue so we can all put it behind us and move on.

As you can see from my previous post, I did uninstall & reinstall the USB hubs just like you did but it didn't help me.

I still haven't received the usb card that I ordered. When I do I will play with it and see what I can learn.

In the meantime, I did find a port replicator for the problem machine (It is a Compaq laptop). When I connected the replicator, the problem went away and the machine now works ok.

I called together some very talented people that I know who professionally work on Avid video computer systems (Media Composer, Issis, Interplay, Air Speeds). I asked them for their opinions & they suggested that I look into USB power.

You can see how much current a device is drawing in Device Manager. I looked at a properly functioning mbox & it was pulling 498 ma. The limit for USB is 500 ma. That's real close. Just a small change in room temperature might be enough to push the mbox over the limit. Note that all computers & the mbox have VOLTAGE regulators to tightly control the voltages they use BUT current can go all over the place in response to what the devices need. Aging of polar capacitors in either the computer or the mbox MAY make them leaky. In that case, they may seem to work ok but they will draw more current.

The problem here is that although the USB spec defines 500ma as the limit, different cards handle that differently. When a device tries to draw more than 500 ma, some cards will just let it do that as much as they can provide. Others may not be able to do it and go into current limit with pretty much unpredictable results in what will happen to the interface. Others will switch the external device down to 100 ma. Still other shut down the device entirely until the computer is restarted. Yeah, it is a big problem for manufacturers to design equipment with all of these variables.

One more thing...... All of these hgih-current USB devices start up with a limit of 100 ma. They then request additional current and if the hub can give it to them, the hub switches them up to high current. I'm guessing that what we are seeing is the situation where the hub senses an over-current violation & switches the mbox back to 100 ma so it just tries over and over again to initialize a higher current-----evidenced by the light display.

When I get a little more time, I will cut open a USB cable so I can insert an ammeter (you can't use device manager to measure current if the device hasn't started). I will try to verify these speculations and maybe I can come up with a really solid diagnostic procedure and maybe a list of some known good cards that work with the mbox.

I will post whatever I learn here.

IHTH
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