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Caught between a rock & a hard place: PRAM battery in 540c

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Hi all,


 Over the Christmas I decided to upgrade my PB 540c. I have a 16MB card to replace the 8MB card and a SCSI2SD PowerBook card to replace the 320MB 2.5" SCSI drive. Neither of these need replacing (12MB is fine for System 7.1.1 and 320MB is more than big enough for the games being played on it. It's not even all that loud.).


While following the iFixit guide, I think I broke the little clippy things that hold in the keyboard strips and I have broken the plastic doodah that holds down the RAM board.

I should know better. This is 26 year-old plastic. I have 2x PM8100s with broken bezels to testify to plastic of this era.

However, I am not here to moan (although I would like to go outside and give off a wild barbaric yawp). We need an 'I could just cry...' forum category - a forum to mirror the joys of conquest with the misfortune of postage, the arrogance of inexperience as well as the ravages of time.


Instead, I would like your opinion and this may fall into the damned-if-you-do-and-damned-if-you-don't-category of questions:

 Should I attempt to take out/replace the PRAM battery?

Ordinarily, I would just do it. I've had exploded batteries in a IIci and a IIsi (sniff) and I should know better to have stored them with the batteries left in. I have spare ½AA 3.6V batteries that are reasonably new (I bought them in 2014). I don't even mind so much not being able to turn on an old Mac with the keyboard. PRAM batteries afford little luxuries, but my IIci with damaged motherboard is not worth it.


Now, I'm fairly sure that more plastic pieces will break when I try to dissemble it, especially the bezels.

There are surely members who have taken 500 series apart recently and know firsthand in what shape the plastics are in.

What is your opinion?


Thanks everyone and I would like to wish you all a peaceful new year.


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This is a tricky problem! I think I would still attempt to remove the PRAM battery, despite the very brittle plastics. There is no absolute guarantee that the plastics will break, or that the battery will leak, but I personally would much rather glue plastics back together than repair a logic board with battery acid damage. I definitely wouldn't install a new battery if it isn't necessary for the machine to turn on. I wonder if very slightly heating the clips with a hairdryer would be enough to make them a bit more flexible during the disassembly process? Presumably, cold plastic is slightly more brittle than warm plastic -of course it the plastic gets too hot, it will just melt, which would be a lot harder to remedy than repairing cracked plastic.

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I’ve been thinking about doing this in my Blackbird also .... it’s been a while but don’t they take a custom battery of some sort?  Where did you get the replacement part?  I also recall it being extremely hard to get to so I’ve been putting it off for over a year now ...

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3 hours ago, Crutch said:

I’ve been thinking about doing this in my Blackbird also .... it’s been a while but don’t they take a custom battery of some sort?  Where did you get the replacement part?  I also recall it being extremely hard to get to so I’ve been putting it off for over a year now ...

I had been making two assumptions: 1. that it will start without a PRAM battery 2. that the PRAM battery is one of the standard ½AA 3.6V batteries that Apple seems to have use in every Mac up to relatively recently.


It seems that you are right: https://www.applemacparts.co.uk/powerbook-5xx-backup-clock-battery-

I don't have a replacement.

I have to check now if assumption 1 is also wrong (i.e. that it needs a PRAM battery to start).

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The 500 series was the first of the PowerBooks to use the familiar brown plastic-encased 3-wire rechargeable batteries instead of the old soldered button cells (or the removable multi-cell arrangement of the 100 or the 9v used by the Portable). They live above one of the batteries in the top case behind a clip-in retainer. Complete disassembly is required to get to it though since you need to remove pretty much everything to get the top case off. As long as you don't Hulk torque any of the fasteners the plastics on those hold up pretty well, save for the display mounts, and even those wouldn't be so bad if the hinges didn't become so stiff with age. The most fragile piece of plastic is usually the little bar for the RAM retainer/heatsink holder, but seeing as how most of those are warped from being hot and over-tightened for 30 years they don't stand much of a chance of surviving much manipulation. Also if you're not careful in disassembly the keyboard trim piece thing, clutch covers, and display lower cover can also become broken very easily. Often I end up breaking the rear tab off of at least one of the clutch covers, typically the right one over the display cable.

Anyway those machines don't miss a PRAM battery; they either keep their settings with the help of a main battery (if available) or while plugged in, or they simply revert to defaults on next boot if it was left unpowered. Of course even with a good PRAM battery an average PowerBook would lose its settings after no more than 30 days off AC and that's with a fully-charged main battery along with a fully-charged PRAM battery.

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  • 2 weeks later...

I've taken two partially apart recently: a 540c and a 550c. I certainly held my breath pulling off those clutch covers and rotating the screen down to the lowest position. I did not find the internal plastic bits to be in brittle shape, considering the age. I use my PM8500 as the worst case example. It's plastic will crack with a thought.


I'm in a similar situation: I replaced the RAM, HD, and processor in the 550. The idea of taking it entirely apart (especially after my 2400c issue afterwards) is not appealing. At the moment, my school of thought it to leave well enough alone. The battery hasn't leaked to this point and in my experience with 5 Macs (1989-1997) I have yet find a leaking battery. The fact that its above the right bay and not sitting in the middle of the board makes it less of a worry for me.

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