Backup battery discharged -> GTA01 and GTA02 dead

Rod Whitby rod at
Mon Jul 21 13:32:26 CEST 2008

Werner Almesberger wrote:
> Rod Whitby wrote:
>> but never as a result of the normal NOR boot sequence.
> Has it ever booted from NOR (before it started to act strangely) ?

Yes, for a number of weeks after I got it, it worked fine.  I could do 
NAND and NOR boots with no problems.  I went overseas for a couple of 
weeks, during which it discharged both main and backup battery 
completely, and when I returned it wouldn't boot.  It hasn't booted 
since until I left it overnight to recharge the backup battery, and then 
I started to get the very rare booting condition.

>> *Never* have I been able to get it to boot twice in a row.
> That sounds bad :-( I've seen systems behaves like yours, but they
> were usually afflicted with some hardware problem. Normally, it's
> the VB_SYS cap Andy mentioned.
> Just to check: is this GTA02 a mass-production device or a preview
> model ? Could you please mail the serial number ?

Serial number is 8B8313262.  This is a preview model, but looked like it 
came off the mass-production line (it was in the final box with all 
accessories, and is in no way marked like a prototype).

>> I'm monitoring the nRESET line at various points in the sequence above,  
>> and I've never seen it go above 0V.
> That would be consistent with the capacitor problem. (But could be
> a number of other things as well.) I guess you don't have an
> oscilloscope you could attach to watch it continuously for you ?

I do have a scope probe for a 16650 logic analyser at work, and will 
look at setting it up in the next few days to see if there are any 
pulses on nRESET - is that what I should be looking for?  What other 
signals should I be using as a trigger or tracing alongside nRESET?

>> Knowing that the batteries and usb charger are fine, and that nRESET is  
>> still low, what's the next level of debugging I can try - how do I work  
>> back from the nRESET test point to the PMU pins to find out what's going  
>> wrong?
> Hmm, that's the point where I'd start watching voltage levels with
> a scope, and maybe have look the the capacitors under the shield ...

I'm happy to keep probing here to find the problem, but I don't have SMT 
rework equipment to fix anything serious.  If it's a missing cap that 
could be scavenged from a GTA01 (I have two of those that don't work 
either) then I'm up to trying to solder that on (I have a temp 
controlled station with a 1mm tip and a steady hand).

Which shield do I start lifting ;-)

-- Rod

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