iMac G3 backup battery

[Apostrophe]

Hi,

I'm in a good mood; today me and my dad were over at the house we're trying to sell, to clean up the yard and stuff. While there, I picked up our hp Photosmart printer. I brought it back to our house (the one we live in) and installed it onto the iMac G3. That brings me up to two printers; the hp DeskWriter for the Mac SE and Centris 610, and the Photosmart for the iMac. I can now print no matter which computer I use!

But I still have a list of things to do and get for various computers, and I would like to ask you about one of them. The iMac G3 never remembers the time whenever I set it. It'll remember it for a few days at a time, but in the end it always reverts back to sometime in 1904.

The problem is probably the backup battery, based on this forum and the help menu of the iMac. It just occurred to me that if there's a battery leaking in there somewhere, it could cause damage. So sometime tomorrow I'll open the iMac and see what the issue is. But I was wondering, if I actually find a leaking battery, can the iMac still boot and function without it? If I find a leaking battery, I'll obviously remove it to prevent any damage. What's the battery's function, anyway?

Thanks,

-Apostrophe

 

[luddite]

I don't think there's any difference between a dead battery and no battery in an iMac, it should still boot.

It's the same 3.6 v battery that they've been using forever, so luckily they're not hard to find. Also not hard to replace.

 

[Apostrophe]

Ok, thanks, once I get back from our camping trip I'll open up the iMac and see if there's a dead battery.

-Apostrophe

 

[equill]

3.6-V primary cells such as the half-AA lithium thionyl chloride battery used for PRAM maintenance and time-keeping in Macs rarely leak, even after declining to voltages such as 0.1 and below. This decline happens when Macs are left in storage for years without a live mains connection. In normal use the battery is 'spared', that is, reverse-biased, behind a diode, by the Mac's PSU so that the battery does not have to supply current. In that state it can achieve a working lifetime almost equivalent to its shelf life of several years before it reaches the advisable chuckaway point of 3.3V in circuit.

In those Macs with a PMU rather than a CUDA switch, pressing the reset button more than once (or letting it 'bounce' when pressed) can deplete the battery within two days instead of several years. When you replace the battery in your iMac, which should be soon—battery replacement, at USD4 from eBay sellers, is one of the most trifling expenses in keeping a Mac—take care when you reset the PMU. One press only, for a second or so, is all that is needed. If you do, by mischance, press more than once you will need to reset the logic board and PMU by removing all power for 10min. or so, and then press the switch once after reconnecting power and battery.

Your iMac without a battery will lose track of time, unless it is set to get time from a server such as Apple's at startup, only if it is switched off between uses, and not if it sleeps between uses. However, system parameters kept in PRAM will not be maintained well, or will be maintained not-at-all, without a functional battery.

de

 

[Christopher]

As long as the mac is plugged in I'd should be ok.

 

[Apostrophe]

Hi,

Ok, in a bit I'll open the iMac and see if there's a dead battery. (Even if it's fine, I'll probably replace it anyway.)

Now, you mentioned resetting the PMU. Let me remind you that I am quite a newbie at Macs. I mean, I have fixed problems that have occurred with my Macs in the past, but that was just because they all had to do with replacing parts or reinstalling OSes, both of which are easy.

So what is PMU? Or, to expand on that, once I physically replace the battery and put the Mac back together, what do I need to do?

Thanks,

-Apostrophe

 

[Apostrophe]

Ok, I just opened up the iMac (I accidentally cracked some plastic off while lifting off the bottom housing, but don't worry, the iMac still works just as it did before), and had a look at the logic board. Wow, those capacitors are HUGE! Anyway, I saw the battery and recorded its information. I didn't actually take it out, since I don't want to have anything to do with the PMU just yet (I know what it is and the procedure now, don't worry). Where can I get a replacement?

Yes, I'm sure the battery is dead, after I had a look at the page that helped me disassemble the iMac. Here is an excerpt:

From www.scribd.com/doc/103447/iMac-G3-Disassembly-Guide:

"The battery on the logic board controls the stored system settings, such as date and time. It is only necessary to test the battery when you can't power on the computer, or the date and time are reset every time the AC power is removed.

The battery is also used to power the PMU chip (because the PMU chip keeps time and must always be running) when the computer is unplugged from the wall (AC power). The PMU is very sensitive and touching any circuitry that is connected to the PMU can cause it to crash. If the PMU crashes, the battery life goes from about five years to about two days if the PMU is not reset. Once the battery goes dead, the PMU will reset the time and date to 12:00 AM 1/1/04 every time the AC power is removed. To fix this situation, replace the battery and reset the PMU (refer to "Resetting the PMU on the Logic Board" mentioned earlier in this chapter)."

Notice the segment that says that the clock will read January first, 1904 if the battery is dead. In my first post, I mentioned that the clock reverts back to sometime in 1904. And I just checked the iMac upstairs: that is the time and date that it reads. I'm pretty sure I'm dealing with a dead battery.

Where do you think I can get a replacement?

-Edit: Never mind, I got one on Amazon for 8 dollars including shipping.

Thanks,

-Apostrophe