usb-6501: I'm getting 2 Hz noise from blinking LED. How can I get it to stop blinking?

[SLF]

Hi,

We are using a USB-6501 OEM D I/O board to control a sensitive measurement device (basically a simplified 3 GHz network analyzer).  The analog output of our device has a 2 Hz, 50% duty cycle square wave that correlates exactly with the on/off state of the LED (measured with a photodiode and a scope).  I don't know the coupling mechanism, but additional shielding between the NI board and ours helped somewhat.  I also don't know if the root cause is the diode itself, or something about the electronics driving the diode.

Is there a way to get the LED to stop blinking?  Is the blinking triggered by something from the PC (running Windows 7 or XP), such as the USB controller polling the USB-6501, or is this something being done by the USB-6501 itself?  Is there some config parameter we can change in the Labview code we use to control the board (using DAQmx 9.1.0).  I have a PC with DAQmx 9.1.7f2 but have not looked at the noise with it yet.

The brute force test we are contemplating is removing the diode from the board....

Any suggestions or pointers would be most welcome.

Thanks,

Stuart

[Seth_B.]

The blinking of this LED is intended to indicate that the board is active and is controlled by the hardware of the board itself and can't be disabled using the driver.  It's possible that desoldering the LED would reduce the noise to acceptable levels, but would likely also void the warrantee.  It's be something to test.