2.2 - Status LED [U3 Datasheet] | LabJack
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2.2 - Status LED [U3 Datasheet]

There is a green status LED on the LabJack U3. This LED blinks on reset, and then remains steadily lit. Other LED behavior is generally related to flash upgrade modes (Section 1.2).

Normal  power-up Status LED behavior: When the USB cable is connected to the U3, the Status LED blinks 5-6 times over 2 seconds and then remains solid on.

Normal power-up Status LED behavior but device keeps rebooting, even with no connections besides USB:  You might notice this because you see the normal power-up LED behavior happening repeatedly and perhaps also hear the host making noises as the device disconnects and reconnects.  Likely indicates that the Watchdog is resetting the device.  To reset to factory default values (i.e. disable watchdog), power up the U3 with a jumper securely installed from FIO6 to SPC (FIO2 to SCL on U3 1.20/1.21), then remove the jumper and power cycle the device again.

Status LED blinking continuously at about 4 Hz, even with no software running: This indicates that the U3 is in flash mode. See Section 1.2 and reprogram the device.

Other or no Status LED behavior, even with no connections besides USB:  Try using the different jumpers and reprogramming as described in Section 1.2.  If you get no LED activity with any jumpers, but know the USB port is good and providing 5 volts, the device is likely damaged beyond field repair possibility (returns, exchanges, and repairs).  Also see item F in the USB Communication Failure App Note.



When I connect my labjack to the computer the status LED blinks a few times and then stops glowing. My computer fails to detect LabJack. Everything was working fine until this one time when it suddenly stopped working. Any clue what could be wrong?

Do all troubleshooting with nothing connected except USB.

First install the UD driver on a different computer with a different cable, then try connecting the U3 to that computer.

The other thing to try is using LJSelfUpgrade to reprogram.  Try the different jumpers mentioned in step #2 of the LJSelfUpgrade page.

Beyond that, contact [email protected].

Thanks for the reply. Turns out, restarting windows worked!

If it happens again, see if it is enough to disconnect/reconnect the USB cable from the U3, or if you have to restart the computer.

Sounds like the USB sub-system on your computer was confuzzed.  What version of Windows?

Reconnecting the USB cable did not help, even on different USB ports. The VI that I was using to read out labjack ports returned a communication error, and the LJControlPanel did not detect labjack. This is on Windows 7.

OK.  Used to have some problems on XP related to Windows bugs with selective suspend and power save, but have not seen any such issues on Windows 7.  Just in case, though, for the sake of long-term operation you might want to "disable usb selective suspend", and even disable as many windows power saving features as you are willing to disable.