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Older Mac Magic Keyboard

March 19, 2022

I thought I would post this as it might come in handy to some other folks. I have a couple of older Macintosh “Magic” keyboards from as far back as around 2012. These are handy Bluetooth keyboards that work very well with iPads, iPhones as well as being used with iMac computers.

The problem comes if you leave batteries past their prime in one of these keyboards. They take two AA batteries and the batteries are held in with a screw-in plug. If the 2nd battery leaks, it can get into the threads of the screw and make it very difficult to remove the plug to change the batteries.

Very difficult is an understatement. The “recommended” tool for undoing the screw-in plug is a coin. I tried a coin – no go. I tried various screwdrivers. I tried using a US dime held in a pliers – I bent the dime.

I ended up taking the keyboard to a nearby Apple store. They tried – nothing. They looked it up and tried to see if a replacement might be possible. Nope, too old. A new keyboard was suggested. New Bluetooth keyboard wasn’t cheap, but one doesn’t expect “cheap” in an Apple store.

I am not a person that likes to throw things away when they are possible to repair. I fix them. I fix a lot of things. But I was quite discouraged from my trip to the Apple store. I started thinking of different ways to remove this screwed in plug, such as using a screw extractor or drilling two tiny holes to use a spanner wrench sort of thing.

I was just about ready to toss the keyboard in the trash as being unrepairable and impractical to try. I did put an order in for a new wired keyboard for my iMac computer.

Then it hit me. Thermal expansion. The keyboard has an aluminum base and the plug is aluminum as well. Fits fairly tightly and there is likely enough thermal conductivity between these parts that the thin aluminum of the case is going to pretty much be at the same temperature as the plug. As it turns out, this isn’t exactly true.

I put the keyboard in the refrigerator for a bit. Actually, I was travelling the next two days so it say in their and got nice and cold. I took it out and tried a big screwdriver on the plug and it instantly turned. I think I probably held the aluminum case some so it warmed up, but there was clearly some temperature differential between the case and the plug. It was a little crusty from the battery leakage, but it turned and was able to be removed.

Aluminum, it turns out, has a thermal expansion coefficient of 69 x 10-6 /°C. This is more than double the coefficient of iron, which is 33.3 x 10-6 /°C. Not to put too fine a point on it, aluminum shrinks and expands due to temperature more than twice as much as iron does. This is why I was able to remove the plug when it was cold and the keyboard frame was a bit warmer. The plug shrank a bit and likely broke the adhesion between the plug and the case. Warming up the frame of the keyboard helped too.

Some vinegar was applied to both parts and the battery leakage removed. Alkaline battery leakage is quite easily removed with ordinary white vinegar.

Works fine now.

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