Intel486dx33 wrote on 2022-02-22, 21:06:Hey Guys,
I have another NOS 486 motherboard with a Dead Dallas.
It does not have connection pins for an external battery but th […]
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Hey Guys,
I have another NOS 486 motherboard with a Dead Dallas.
It does not have connection pins for an external battery but the markings are there for a jumper and traces for an external
Battery connection. PLEASE SEE PHOTOS.
I was wondering if I could add an external battery by soldering onto the motherboard and wires for an external battery ?
And soldering on a wire for the jumper ?
It's possible that those are for a version of the RTC with a clear function (12887A maybe?). I guess that R2 pulls pin 1 of J10 high and that fitting a jumper will connect pin 1 to Ground, which if pin 1 goes to pin 21 of the RTC would clear the CMOS. I don't think any of the Dallas chips have any pins for an external battery, hence the various mods involving cutting in to the casing to get at the internal battery points.
You can check if I've guessed right by measuring the resistance from J10 pin 1 to the Dallas pin 21. If they're connected then it's CMOS clear. If they're not connected then it might be interesting to find out what J10 does connect to.