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Old 03-21-2020, 09:39 AM   #6
Join Date: Jan 2016
City & State: Valbonne, 06
My Country: France
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Posts: 2,119
Default Re: Anyone have schematic/boardview MS-6178?

Yes that's usually how it looks like, so that RTC power rail is fed from the power supply (5VSB converted to 3VSB) when plugged in to the mains, and backed up by the coin cell battery when disconnected from the mains. I've already seen cases where the dual diode becomes leaky between coin cell battery and 3VSB, effectively discharging the coin cell battery into 3VSB.
Or the usual case of southbridge going short on RTC power rail…
The coin cell battery itself can be connected directly to one of the SIO pin to monitor its voltage. But it's not supposed to actually supply power to it, as power should be taken from 3VSB directly, SIO shouldn't need a battery backup.
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