Re: [Paparazzi-devel] Umarim testing

[Gareth Roberts]

Hi David,

I have 10 umarims that were made up at a fab house.
Of the 10, 6 had the short circuit issue described in the wiki (I added the 
note, attached is the diagram from the fab house).
I didn't want to report the issues with the gerbers on the mailing list until I 
was sure of the issue, but didn't want anyone wasting money getting potentially 
problematic PCBs made up!

For those who don't know, the pads of the ITG-3200 on the board extend 
underneath the QFN package.  Normally this wouldn't be a problem, but the ITG 
has a metallic base.  
The clearance is 0.025mm, which is less than the tolerance of the fab house I 
used.  I can't correct the issue (other than by directly messing with the 
gerbers) as I don't have access to Protel, which the files were created in.

I haven't flown yet in case vibration or moisture caused the 'good'  boards to 
short mid-flight.
The boards have now been reworked and kaptan tape added to the base of the 
ITG's, so we'll be flight testing shortly.

I did do some ground testing with the board & a level shifted serial cable, and 
everything worked as you described (haven't checked baro though).
I've also programmed one via UART-1. which worked.

It may be possible that as the board heated up slightly on your burn-in test 
the expansion caused the ITG to short.  The 3.3V converter is short-protected 
but does get hot in this condition (although doesn't burn out) and heats the 
rest of the board up.  Once you switched everything off and the board cooled 
down, everything would work again.  It may at least be worth checking (just pop 
the umarim in the oven at a low temperature and do a continuity check on the 
outputs of the 3.3V regulator once it's warm).

Again, I would be deeply suspicious of that ITG.  I'd recommend the kaptan tape 
even if you aren't sure.
I can try running a burn in test @ 13.5V with my Umarims on Monday (I've run 
them for a couple of hours, but at 8.5V).
If there is anything else I can do to help, please let me know & keep me 
updated, as I'm planning to start flight testing this week.

Cheers,
Gareth

umarim.pdf
Description: umarim.pdf