[Discuss-gnuradio] USRP + case = electrical short??

[Weber, Michael J. \(US SSA\)]

Hello,

I have a USRP with an RFX2400 mounted on the A side and a FLEX900
mounted on the B side. Everything works great UNTIL I connect the SMA
jumpers from a TX/RX port on either board to the case. When the
connection between the TX/RX ground and the case is made, a short
occurs, the regulator gets very hot, and the voltage at the input jack
drops to about 2V. Of course I disconnected the power as soon as I
discovered what was happening. The board seems happy out of the case, or
even in the case if the antenna port jumpers are not installed. I have
to other units just like this one running with no problems, though one
of them has a FLEX400 instead of a FLEX900. 

So... any ideas where the short is? I inspected the case and USRP but
didn't see anything telling, but there's a lot of tiny components and
traces.

Help?

Thanks,
Mike

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Mike Weber * 703-668-4516
Network Engineer, BAE Systems