...seen anything like this before? Any ideas on what it might be? At this point, I'm down to a logic board or component-level issue, ...

Click to expand...

Umm, no, yes, and agree. Sounds like a hardware problem to me also. An easy second step while you are experimenting with the battery is to do a topside visual board inspection around the battery, crystal, 8 pin RTC chip if you have one right next to the crystal, looking for capacitor wet residue, corrosion, foreign matter shorting out the crystal, oscillator or the one second interrupt to the VIA interface chip. By the way, that RTC is where the PRAM lives also, so if it remembers mouse settings and other stuff maybe the chip is powered and backed up okay but the oscillator is not going, stopping time as it were. I think the VIA externally serial clocks the PRAM data in and out. If you have Guide to the Macintosh Family Hardware, Second Ed, see p144. I can walk you thru the pinouts if need be.