The Onyx Firewire card installed in the 1620 mixer is sending a low left channel signal back to the mixer. It use to work fine but not anymore. I have this same problem on my Mac tower G4 and powermac laptop. No updates have been added to the laptop and it use to work. No one on the forums has an answer although several have the same issue. Mac tech support doesn't respond.

If it's not the cables that you are using, it could be a number of things. Bad solder connection or corrosion on one or more ribbon cables. Maybe a weak return contact on a 1/4 inch female jack. Try putting a signal into the mixer and then inserting a male 1/4 inch plug into the different jacks to find out which jacks disconnect the signal when inserted. Even when they are not used these jacks tend to become slightly corroded and the signal is lost. You can give the jacks a burst of contact spray and 'work' a male plug in and out of the jack a dozen times.

Don't think it's a heat problem; sometimes the electronics just get confused and need to have power cycled. Try turning power off at the rocker switch, wait 10 secs., then turn it back on. If that doesn't clear the problem, try the same thing by unplugging the AC cord. If nothing changes, it may be time to call LOUD tech support - 1.800.898.3211

Are you actually sending a signal to the effects unit? normally you would have it in an insert although I know some people who take a sub channel out to the effects unit and then feed it back in through a mix channel if they run out of inserts or aux busses. What you describe above does not make sense to me. Can you elaborate with the full signal path for the effects unit?

Check in the computer "Device manager" if a PC with windows, and see if there are any devices with an yellow "X" through them- the port may have an interrupt conflict.

Then check audio properties of the system to make sure the devices are selected and enabled, and their volume level is up- even if you are operating through the Mackie software console.

If a Mac- check the Chooser to make sure that input device has been selected.

I am assuming a Windows operating system for this solution.
This sounds like it could be a driver problem (not with the FireWire port, but for the sound card itself).
When you connect the card with the FireWire cable, do you hear a sound from your computer registering the new hardware (assuming this isn't your primary sound card)? Head to the Device Manager (go to Start/Run and enter devmgmt.msc) after plugging in the card and look for any "Unknown Device"s with Yellow "!" triangles next to them (or anything else with a "!" or "?" for that matter). If you find one, try reinstalling the drivers for the corresponding device.
Even if the problem you find seems unrelated, take steps to resolve it anyway. Computers, being as twisted as they are, tend to mess up all kinds of things when certain drivers are out of place.
Also, even if you can't find any problems in the Device Manager, try reinstalling the drivers anyway, and be sure to visit your product manufacturer's website for updated drivers.
Good luck!

The Mackie 1620,1640 or 1220 mixers are designed to be used with this card. Here is a link for you:http://www.mackie.com/products/onyxfirewire/

It is the unit.

I have had this same problem. I don't have a fix for it, but I have noticed that I can make it go away if I increase the signal strength going back to the Mackie card to an extreme level (by spiking the volume on my cubase software mixer). This seems to make the connection better for some reason.
I would love to learn what is causing this.

install drivers with device disconected

Sometimes Windows XP will seem to "forget" that you have Mackie drivers. In such cases you need to go into Hardware Manager, uninstall the drivers, then press F5 to check for hardware changes. It will find the drivers again and take you through the installation process. Sometimes this "forgetting" seems to be triggered by the order in which you turn on the computer and board. It seems that for the first version of the Onyx drivers I had to turn the board on first, then the computer. I have updated my Onyx drivers and now it seems that I must turn on the board after XP is loaded and ready to go. Otherwise Windows can't "see" that the board is attached and thus Sonar or whatever won't be able to record. Sometimes when this happens I can turn the board off and back on, then Windows sees it. However, when that fails I uninstall and reinstall the drivers as I described earlier and it always solves the problem.