Backup battery discharged -> GTA01 and GTA02 dead

Andy Green andy at
Mon Jul 21 15:30:02 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| Andy Green wrote:
|> Somebody in the thread at some point said:
|> |> If it ain't there (or maybe fell off?) you need to add one.
|> |
|> | Can is off, and it looks like the VB_SYS cap is there.  It's a medium
|> | size cap, which looks like it's been soldered on top of the placed
|> | smaller caps.  Which end of it should I check for VB_SYS?  Left or
|> right
|> | in your picture?
|> Right... I guess it would be easier if it had fell off :-)  Oh well.
|> As a test, you could stick another cap in parallel with the flying one
|> and see if it helps.  - end of cap would go on left, which is 0V.
| I'm measuring the voltage at the right end of the VB_SYS cap with a
| voltmeter (I'm at home, so don't have a scope handy).  It seems to be
| fluctuating between 3.7ish volts and 5V.  Does that give any clue?

Sounds like the VB_SYS "trap" and the battery is not filling in enough.

| Any other test points under the can that I should check?

I can't recommend this, but what I would do is briefly short V+
testpoint near USB socket (it is 5V from the host PC) to the +ve battery
terminal nearest the edge (with no actual battery involved) and then try
start up.  It'll probably die again a few seconds after, but you could
stick a battery in by then at it should be OK.

The reason I would do it the VB_SYS "trap" behaviour this seems
reminiscent of comes if the battery is unable to smooth out the dip at
startup for whatever reason, but usually the Host PC can provide 1A or
whatever for a few ms that are needed.

- -Andy
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