MacPro Kbd stops working in one usb hub

[RichC]

I have a lot of usb stuff strung out: 6 kbds, 5 mice (three kinds), 4 audio interfaces, 7 hubs not counting in kbds, etc.; most powered. At the root of the USB tree is a KVM switch feeding a new MacBook (10.5.2) and a G5-Quad (10.4.11) This all pretty much works fine and runs for weeks without hiccup.

But tonight, one MacPro kbd, quit. It's at the end of the chain, but it has been working fine. Plugged into hub one level up it's fine. A new Apple thin-flat kbd plugged in where it was works fine.

When MacPro kbd plugged in, the light on the hub port flashes. Other stuff (Wacom tablet, Insignia speakers) works fine and lights the lights. With other stuff pulled (use less power?) kbd fails the same.

So what's up with this sort of problem, and how does one trace/debug? Usually, when (once in a while) there's a USB problem, just unplug and plug back in and it works again.

Is there a limit on levels in the tree? Power? How do you tell?

Many thanks for any enlightenment. -Dick

[DeltaMac]

USB, in theory, supports up to 127 devices, which would include hubs. Even with 7-port hubs, that's a lot of layers, so bus-powered hubs would be more sensitive, I suppose.
Have you tried swapping hubs around?
If the same keyboard causes the hub to lock out the port, and other devices are functioning OK on that same hub, then bad keyboard.
If the keyboard works OK on other hubs, but not on that hub, then the hub may be failing, or the keyboard might still be bad, and may eventually fail regardless of the hub position.
How much time do you want to waste? There's lots of possible combinations that might affect what you have.
I would replace both that hub _and_ the keyboard at the same time.