Gradually underpowered USB?

[paintballmjm]

Hey everyone,

I've been having a problem with my USB ports that I haven't been able to find a solution to yet. The desktop in question is an early 2008 Mac Pro (more specs in my description; ask if you need more). Over the past couple months, I've noticed that my USB soundcard (Lexicon Lambda) has been popping/crackling more and more, and recently has become completely useless for any kind of audio work. At first I thought it was the soundcard itself, but it works perfectly fine on my Late 2011 MBP. By now, it will only turn on when plugged into the back ports. Similarly, with my Axiom Pro 61 MIDI controller, while it does power on from all of the ports, it is only recognized in the back ports. I'd also like to note that the front/back Firewire 400/800 ports are working perfectly. I know that it's common for the front USB ports to start failing after a couple of years, but for both front and back to do this almost simultaneously seems a bit odd.

Some additional details:

-The front/back Firewire 400/800 ports are functioning perfectly.
-This problem has gradually worsened over time and did not happen instantaneously.
-Zapping the PRAM, resetting the SMC, and installing a new PRAM battery had no effect.
-I've reinstalled Lion on a brand new hard drive (the original HD was on its way out) and repaired the disk and permissions.
-Occasionally, my Magic Mouse and Wireless Keyboard will disconnect and reconnect momentarily. I'm not entirely sure, but I think the bluetooth adapter is powered through a USB bus.
-I no longer have AppleCare and my warranty has obviously expired.

So, since only the USB ports are increasinly underpowered (SATA, Firewire, Line Out, Ethernet, etc are fine), what would be the best course of action? I'm comfortable with disassembly and reassembly to narrow down a solution. Please let me know if you need any additional details.

Thank you very much!

Michael

 

[drewsof07]

I would check the connections to the front I/O board, focusing primarily on both the Logic Board and front panel. There is probably just failing wiring, seeing as the rear ports (direct to mobo) work fine.

 

[goMac]

How much other stuff do you have plugged in over USB? It could be that there are just too many devices and bandwidth is being constrained.

 

[paintballmjm]

I would check the connections to the front I/O board, focusing primarily on both the Logic Board and front panel. There is probably just failing wiring, seeing as the rear ports (direct to mobo) work fine.

I'll definitely give that a try. However, the rear ports are also having issues with underpowering. Although they do provide enough power to power on the soundcard, when audio begins streaming through it (which, I'm guessing, would cause it to require even more power), the audio becomes distorted. The same problem occurs when plugging a USB-powered hard drive to the rear ports and with the occasional Bluetooth disconnects. Thank you for your suggestion though!

Michael

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How much other stuff do you have plugged in over USB? It could be that there are just too many devices and bandwidth is being constrained.

Oh yes, I did forget to mention that. I've tried the USB devices such as the soundcard and the MIDI controller with no other devices plugged in, even firewire because I'm paranoid.

 

[drewsof07]

There is always the possibility your bus controller is going bad, in which case you'll have to get a PCI based USB card. I don't know if the bluetooth or wifi cards are run from the same bus. They use a mini PCI-e connection and should be run by the PCI controller, but i'm not 100% on that.

Also, the bluetooth was terrible on those machines. I couldn't keep my magic mouse connected to save my life. Antennas stuck inside the solid aluminum chassis were not the best engineering decisions on Apples part... haha

 

[paintballmjm]

There is always the possibility your bus controller is going bad, in which case you'll have to get a PCI based USB card. I don't know if the bluetooth or wifi cards are run from the same bus. They use a mini PCI-e connection and should be run by the PCI controller, but i'm not 100% on that.

Also, the bluetooth was terrible on those machines. I couldn't keep my magic mouse connected to save my life. Antennas stuck inside the solid aluminum chassis were not the best engineering decisions on Apples part... haha

I'm definitely considering the PCIe USB card. Even in my PC days, I wasn't a fan of onboard anything for this same reason. As far as the Bluetooth goes, it is listed in my Device Manager as attached to a USB bus. Never had a single problem with my wireless devices disconnecting until my USB ports went south. Completely agreed with the antenna placement.

 

[paintballmjm]

Something I noticed today...

For a couple of minutes, when playing music through the Lambda interface, there was a consistently timed, rhythmic distortion. The distortion "timing" was independent of the tempo of the music tracks, so it's not caused by the tracks themselves. It's like the USB output is actually being affected by AC. Has anyone heard of this kind of thing?

Also, I'm thinking of testing my USB ports with a multimeter, but I've heard that they won't actually output full power until a valid device is plugged in and recognized by the controller. Any (preferably nondestructive) ideas?