Backup battery discharged -> GTA01 and GTA02 dead

Rod Whitby rod at
Sat Jul 19 14:29:58 CEST 2008

Will a backup battery voltage of 0.4V or 0.7V instead of 2.0V cause a 
GTA01 or GTA02 to appear to be completely dead and never power on?

I have four openmoko devices (GTA01Bv3, GTA01Bv4-red-pcb, 
GTA01Bv4-green-pcb, GTA02A5), but only one of them works (the 

The GTA02 stopped working a couple of weeks ago, for no apparent reason. 
  Same with the two early GTA01's which stopped working months ago.

I took all four apart tonight to see if I could measure some comparative 
voltages across the four boards and see if that showed anything 
interesting.  At one point, the GTA02 came back to life (which gave me 
hope that it wasn't really dead), but on the next reboot it seemed to 
die again.

Seeing the GTA02 come back to life caused me to measure the in-circuit 
voltage across the backup battery of all four boards, and I found that 
the working GTA01BV4 had a voltage of 2.0V, whereas the non-working 
GTA02 had a voltage of 0.7V and the two old non-working GTA01s both had 
backup battery voltages around 0.4V.

So, is it the case that if the backup battery voltage is below 1.3 V 
(BUB, +/- 0.3V, Backup battery present threshold, from Werner's GTA02 
voltage chart), then the device will not power on no matter what you do?

Is there an easy way that I can test my theory?

Is there a safe way to recharge the backup battery in-circuit when it's 
voltage is this low?

What is the exact type of battery used for the backup battery, and how 
is it attached to the board (it seems to be soldered in) - what is the 
easiest way to detach or desolder the current battery and install a new one?

Will replacing the backup battery on the three "dead" devices bring them 
back to life?

-- Rod

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