Backup battery discharged -> GTA01 and GTA02 dead

[Werner Almesberger]

Rod Whitby wrote:
> 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?

No, it shouldn't have such an effect. But your description does
make me wonder if a sufficiently discharged backup battery might
actually pull down some internal rail in the PMU. That would be
nasty. I'll see if I can create such a scenario.

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

Some people have charged the backup battery by applying power from an
external source. From Seiko's documentation, there are the following
configurations that should work:

2.5V ---[ 3.3kOhm ]---+
                      |
                   Battery
                      |
                     ---

3.0V ---[ 10kOhm ]----+
                      |
                   Battery
                      |
                     ---

Seiko specify a charging time of 72 hours !

> What is the exact type of battery used for the backup battery,

That should be a Seiko HB414.

> and how is it attached to the board (it seems to be soldered in)

Yes, unfortunately.

> - what is the easiest way to detach or desolder the current battery
> and install a new one?

Hmm, it's probably messy. Big component, large thermal capacity, large
soldered surface, heat transfer into the PCB, ...

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

We don't even know why they're dead yet ;-)

- Werner