My laptop reverted to its factory date/time/wallpaper setting - to worry or not?
July 31, 2011 1:24 PM   Subscribe

Cat chewed through my macbook power cord. I tried to fix it, but when I plugged it in it sparked a little bit and then went out. I bought a new charger, and when I booted my mac up, everything was fine except the time and date needed to be reset and my desktop wallpaper had changed to the default background. Should I be worried?

My friend's cat gnawed on my Macbook Pro 60W charger. Some of the wires were exposed. I tried putting some electrical tape on it and plugged it in - and nothing. So I took off the tape and plugged it in again and it sparked, sent some power to my computer, and then went out. The computer was NOT on when I did this. I got a new charger and booted up my laptop - but the date read 7/31/2000 and the desktop had reverted to the default wallpaper. I reset the time and date, and everything else seems to be working just fine.

What happened?

Do I need to do anything? Should I be worried? Do I need to take it to the mac store?

Thank you wonderful people of the internet.
posted by Lutoslawski to Computers & Internet (10 answers total)
Have you restarted it since you reset the date and time? When you shut down your computer, date/time are maintained by the CMOS battery, which can die, or in this case, possibly get fried. If it restarts and remembers everything, you might be okay. I would make sure I had a fresh backup (which you already have, right??) in case the surge did any damage.
posted by misterbrandt at 1:49 PM on July 31, 2011

If you turn it off, remove and reinsert the laptop battery, and then turn it back on again does the problem repeat itself?
posted by alby at 1:54 PM on July 31, 2011

That sounds like the internal battery went completely flat in the time between your attempted repair and plugging in the new charger, but it could also be PRAM/PMU related.
posted by holgate at 2:00 PM on July 31, 2011

[ex Apple tech support] misterbrandt and holgate are entirely correct about the internal battery. I am however highly interested in the desktop background issue - the background you have chosen is stored in a preference file which the loss of battery power should have exactly zero effect on. Have you restarted the computer since recharging your battery? If not, check whether this has any effect. Additionally, if the CMOS battery is indeed drained, your time and date will reset whenever your main battery is fully drained in future. This might not be a big problem, so I'm just saying this as a heads-up.
posted by fearnothing at 2:15 PM on July 31, 2011

Hey guys, thanks!

I've restarted my computer several times - and maybe it's worth mentioning that I never completely drained the battery down (or at least I don't think I did) - and the settings, including the desktop background, are all remembered just fine. It seems like everything is working properly, after several restarts and a complete power down and power up.

I've rarely drained the battery completely down. Are there any other severely negative repercussions if my CMOS battery is drained? Would you recommend getting it fixed (or replaced)? How much would that cost?
posted by Lutoslawski at 2:32 PM on July 31, 2011

Your CMOS battery is a different battery than the laptop battery itself. You can take the battery totally out of a laptop and when you boot up it'll still know what time it is. Draining the laptop battery has nothing to do with the CMOS battery. If you do need to change it, though, it's pretty trivial if you can take the laptop apart to get to the motherboard. Any competent laptop technician should be able to do it in about 10-20 minutes depending on your laptop.
posted by KathrynT at 4:45 PM on July 31, 2011

KathrynT: newer Mac laptops (the unibody models, at least) don't have the traditional button-cell backup battery; instead, they use a capacitor on the logic board.
posted by holgate at 5:17 PM on July 31, 2011

Whoops. Sorry about that. I stand corrected.
posted by KathrynT at 5:26 PM on July 31, 2011

For most PMUs, if they see the wrong input power conditions, they will shutdown and reset. If they do, they'll revert to default, which is what you saw here.

So, if it's a case that the notebook wasn't without power for several days (which is what you'd need to fully drain the main battery and the PMU backup capacitor), then this is what happened.

Thankfully, modern PMUs are very good at handling all sorts of wrong-power situations, and if it's holding settings correctly and the notebook is working, you are just fine.

Sorry about that. I stand corrected.

Yeah, once EDLC supercaps had enough capacitance, and BIOS/PMUs required little enough power, it was a natural switch. No need for battery replacement means no access needed, no removable battery holder (which takes space -- which is priceless in subnotebook design) and so forth -- and no dramatically failing batteries!
posted by eriko at 6:45 AM on August 1, 2011 [1 favorite]

This happened to me ONE WEEK after I bought my new laptop. I guess the macbook power cords taste good to cats? Since I've never had a problem with, say, my ipod cord... Anyway, I don't think you need to take it to the apple store unless you have some serious other problems. It sounds like the battery went down. With mine, I noticed the battery was going down even though it was plugged in, and then I found the chewed up part of the cord so I replaced it before the battery went completely down.

I now have a somewhat complicated arrangement so that the cord is nowhere near the floor and it's been great ever since.
posted by fromageball at 3:42 PM on August 8, 2011

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