[iBook] Yet another problem...

Fred Stevens K2FRD k2frd at mac.com
Sat Jun 3 13:03:33 PDT 2006

At 1:09 PM -0400 6/3/06, Brian Pearce wrote:
>>What's a mobo battery?  No replacement of any battery that I know of.  Reset didn't work.
>It's a reference to a battery on the logic board that provides a small amount of power for essential systems. I don't believe the G4 Powerbooks have one -- they draw a small amount of current from the main battery, instead.

That may not be entirely correct. Modern (as in mid- to late 90s to present) electronics which require sustained/continuous memory for system, preferences, images, etc.) now use EEPROMs (Electrically Erasable Programmable Read-Only Memory), "chips" which are essentially the same as flash or other memory cards such as are found in digital cameras. These hold memory without the use of a memory battery, the latter of which are usually small wafer or hearing aid type batteries. EEPROMs discharge minute amounts of current sufficient to hold memory by use of RC (resistor-capacitor) circuits which discharge at a very slow rate, i.e., months (earlier versions) or years. As the technology improved, the efficiency and length of time an EEPROM would hold memory  is now in the order of ten years or more. I don't know when Apple started using EEPROMs, but I had a 1997 7300 desktop which used the now-outdated battery. My 14" iBook G3 900 uses an EEPROM, but without the schematic, I have no idea where it might be located.

With the advent of the EEPROM, it is no longer necessary to worry about computer memory loss when the memory battery dies and/or the main battery in a laptop or power supply is disconnected. At the user level, there is little a consumer can do about a failed EEPROM (the newer the device, the less likely it is to fail); they're about the size of corn kernel and look like every other tiny black chip on the logic board.


73 de Fred Stevens K2FRD, VO2FS

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