Apple Macintosh LC575 PRAM Battery - Page 1
Forum section: electronics / general

author: Unknown
author_rank: Unknown
timestamp: September 04, 2014, 12:40:30 am
content: This one goes out to anyone who has an old Mac LC575 in their collection.I've acquired one for my own computer collection but the PRAM battery is dead. The one I pulled out of it is aPanasonic BR-E3 6 volt Lithiumpack (see attached picture). It also has a diode soldered and heat shrunk onto the positive lead (which suggests to me that the Macintosh is capable of charging a NiCd pack when powered on). I have no idea if this is the original battery or if someone has replaced it before.After a lot of searching, I'm getting mixed information regarding a replacement battery.Some sources suggest that a 4.5v replacement is needed for the LC575 however this conflicts with the 6v pack I pulled out of the thing. Apple's technical documentation consider a dead battery to be anything under 3v (mine measures 2.3v) but doesn't specify a replacement part or voltage. Will a 6v pack be suitable or has someone done the dodgy and just drained a 6v battery down to 4.5v before installing it?If anyone with an LC575 could have a look to see what they have, that would be most appreciated (it only takes a few seconds to remove the logic board from the back of the system).

author: andrewwong2000
author_rank: Contributor
timestamp: September 04, 2014, 06:54:02 am
content: Google it.. If you can find a stockist $8Sent from my iPhone using Tapatalk

author: Unknown
author_rank: Unknown
timestamp: September 04, 2014, 06:56:21 am
content: Quote from: andrewwong2000 on September 04, 2014, 06:54:02 amThe problem isn't availability, I can just order the battery I need from Element14. The issue is, which battery is it? Some sites say it's a 4.5v pack, yet I pulled out a 6v pack from a working machine. I've even seen a site that quotes 3.6v.I'm an inquisitive kind of person, I want to knowwhybefore I do. Common sense would suggest that you put the same type in that came out of it, however I don't want to blow anything up as I don't know what the state of charge was on the 6v when it was installed (it may not have been full).I guess I could just play it safe and throw a 4.5v pack in, even though it may not last as long.

author: amyk
author_rank: Super Contributor
timestamp: September 04, 2014, 01:10:13 pm
content: I was going to say "Google the datasheet for the chip and look at the max voltage" but then I realised this is Apple who loveto make unobtanium custom-marked parts... but given that it's fabbed by Motorola it's not a bad guess to say it's made on the same process as the classic MC146818, whose datasheet specifies "3V to 6V operation" and an absolute max of 8V.Given there are many other reports on the Internet of people using 6V with no issues, I would go with that. It's low-power CMOS with a big operating voltage range.

author: Unknown
author_rank: Unknown
timestamp: September 04, 2014, 09:58:27 pm
content: Amy, you speak a lot of sense! You've sold me. Element14 even have a 6v pack complete with wire leads ready to go (although I'll need to check that the machine won't try and recharge the thing).