[Discuss-gnuradio] USRP1 USB I/F failure & repair

[Paul Mathews]

About a month ago, our USRP1 Rev. 4.5 (Ser. #2728) became erratic in it USB
connection and communications. A short while after, USB failed altogether. I
put scope probes on the USB + and - data lines and observed that one of the
signals had a much different sort of signal than the other. Following advice
from Matt Ettus given to others who had experienced USB failure, I ordered a
replacement USB chip along with a Chipquik SMD removal kit. Replacement of
the chip had no effect, so I was forced to look more carefully for a cause.
It turns out that one of the 0603 capacitors installed near the USB
receptacle (C73, C74) was shorted, and removal of these 2 capacitors
restored USB function. I'm posting this description of my experiences for
the benefit of others on the list.

I suspect that C73 and C74 (which I can't find in various schematics and
BOMs for USRP1) were added in the hope that they would provide a path for
electrostatic discharges, which is ironic. In my experience, low-capacitance
avalanche breakdown devices are more suitable for this purpose.

I can highly recommend ChipQuik.

Paul Mathews