Three atusb gone bad - the pictures !
werner at almesberger.net
Mon Jun 27 12:13:23 EDT 2011
Today, a little parcel with my atben/atusb boards arrived from
tuxbrain. Among the boards were three atusb that had failed
I had a quick look at them and spotted what are likely causes
for the failures. Fortunately, each of them had a different
problem. Nothing would be more boring than to have to see the
same error over and over again ;-)
The first board looks strong and healthy:
There's just one small flaw: the MCU should face the other way,
as shown here:
That's not impossible to fix but it would be rather messy, so I
think I'll save myself the trouble :)
One to the second board:
Pick and place strikes again. This time by not placing a small
resistor. The USB D+ signal goes through this resistor. Without
it, the board can be flashed, it will power on when plugged into
USB, but it won't be able to communicate. Should be easy to fix.
The third one was a bit more difficult. All looked well until its
troubles were revealed by the spectrum test, which checks the
signal strength across the board's frequency range. 
Closer examination revealed this:
You have to look at it from the right angle or the gap is hardly
visible. A continuity test with a multimeter confirmed that the
pin is not connected. This pin should connect to one half of the
differential RF signal, between transceiver and antenna. Without
it, a tiny bit of RF still makes it to or from the transceiver,
but it's not really usable.
Again, should be easy to fix.
If you're now examining your boards for undetected problems, please
note that atben and atusb each have one unpopulated component. On
atben it's C12, on atusb it's C16:
These are places where capacitors could be added for antenna tuning,
just like the 0 Ohm resistors R1 (atben) or R3 (atusb) could be
replaced with inductors.
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