Fairbanks USB scale reading issue

[Craig]

I have utilized features of the USB library (Generic HID) to read several scales which works great. However, I just encountered an issue with a Fairbanks USB scale - a newer model scale that for some reason I can't get to read properly. I tried to use the sample Generic HID Tester to debug and when I do a send and receive data "once" I get a read. If I try to read again, I get a safe file handle has been closed exception.

I can get other Fairbanks scales (having the same vendor and product id) to read fine and selecting "once" repeatedly from Generic HID Tester. The only difference I can think of is that the one I CAN'T read is powered by the USB port, whereas the other ones have separate power sources.

The scale is operational and can be read by UPS WorldShip, so I have eliminated the hardware. I have also tried to move the scale to a another machine and get the same results.

Any ideas, why I'm having issues reading this one, but can read other types (same vendor and product id) just fine?

[Jan Axelson]

Assuming the scale doesn't require a power supply, be sure to attach it to a high-power host port (most are) or a self-powered hub. (Any port will work if the scale requires 100 mA or less.)

A protocol analyzer would show any errors in the traffic and might offer a clue.

Jan