Repairing the USB Apple Pro Keyboard

by Harvey Chao (Apr 17, 2005)

I just finished repairing a current Apple keyboard - one of the ones that come with current new systems, USB, clear plastic base, all the rest white and held together with (3) 0.050 hex screws on the back. And why, you may rightfully ask, did I do that? Because #3 daughter spilled a cup of water onto it. It immediately stopped working, and after drying out a few days sorta worked but injected extra numeric characters when you pressed certain keys - for example, press the "e" key and you would get "e3", or press "j" and get "j8". Kinda messes up your typing. Why did I mess with it? Because this daughter asked me for a new keyboard, and I said "No" you'll have to replace it yourself. Not a happy camper - either of us! She had no money, I wasn't going to donate any, nor was I going to provide her MY spare keyboard because she was careless! Also, I'm an admitted "bottom feeder" (a polite way to say "cheap"), but since I always harp to the kids that "it is not so much as what you earn, but what you do with what the government lets you keep that counts", I figured I'd better practice what I preached.

First point is that the smallest Allen wrench I had (1/16") was a joke - WAYYYY too big. That was a good excuse for a trip to Fry's - needed to pick up an Ethernet cable anyway. Found a set for $4 that went from 0.050" to 3/16", took it over to the Apple display in Fry's and was able to verify that the 0.050 size was what I needed and so I was on my way.

I got home and did a "Google" advanced search on "apple keyboard repair" and found a good
technology web site for Pro Keyboard Repair. It is for a keyboard of similar construction and had a lot of good information that I took to heart. Unfortunately I didn't take photos of my project, but the above referenced site has plenty of good ones that are close enough to this keyboard to serve the same purpose.

If you do "try this at home kids", be sure to have:

To begin, flip the keyboard over on a flat work surface and remove the three 0.050" Allen screws. Then gently and carefully tip the clear base up and away from you by rotating the front edge up and back.

What you should see is the bottom of the keyboard assembly topped by a steel plate held in place by about 30 or so tiny Phillips head screws. At this point, the keyboard assembly is still attached to the bottom by a pair of multiconnector ribbons that appear to be a thin sheet of flexible plastic with printed circuit traces on them. If you are careful, you can leave this attached. The operative word is "CAREFUL".

Believe it or not, to get to the next level of disassembly, you actually do have to remove all 30 (or however many there are) of those tiny screws. I strongly recommend you put these and the three Allen head screws into a small bowl so that they don't get lost. As you remove the screws, make sure that the keys are resting on a flat surface so that don't come free and become scattered. They actually snap to the top surface of the keyboard, but why mess around? Two of the tiny screws hold a small plastic piece that forms an upside down "U" around the top and sides of the "up" arrow key and this piece of plastic will simply drop down to the work surface - no big deal.

Once all the screws are out, you can carefully remove the steel plate to reveal the two plastic sheets that form the "membrane" where the actual switching contacts take place.

Time out. The two membrane sheets are precision aligned, and that alignment is fixed by a weld in the form of a small ~1/8" dot that adheres the two sheets together. DO NOT BREAK THIS ATTACHMENT!!! If you do, you will probably never get the two sheets properly aligned, and even if you do, they will probably slip out of alignment as you try to reassemble things.

Once the steel plate is off, move it out of the way, clean and dry it as necessary.

Now you are ready to CAREFULLY lift the membrane assembly up off the remainder of the keyboard assembly. Between each key (now upside down) and the membrane assembly will be what appears to be a little "dome" of rubbery material (silicon?), about 108 of them. These are the "springs" that push the keys back up when you release them as you type. They probably will not all stay in place and may adhere to the membrane assembly or simply get pulled out of position. No big deal, just don't loose any and put them all back where they belong, then push the keyboard assembly out of your way so that you can put the switch membrane assembly directly in front of you. You may have to reposition it in any number of orientations to work on it. This is no big deal as long as you are careful in handling it. Remember, it is attached by those two somewhat delicate flat connector ribbons to the small printed circuit assembly (where the 2 USB ports and USB cable are attached).

Using a clean paper towel, and/or the cotton swabs and the alcohol, clean any contamination or remaining contaminating liquid from the inner and outer surfaces of the membrane assembly. I think, in my case, the moisture from the water created contaminates between the two membranes, providing alternate conductive paths that caused the extra numeric characters to be generated. I'm reasonably confident that the technology involved is equally sensitive to the intended circuit traces and switch paths as well as to any stray (even high impedence) path that contamination may create.

In my case, it appeared that most of the contamination was limited to the edges of the membrane assembly, where I cleaned all 4 surfaces (inside and outside) as well as possible with an alcohol soaked swab. You could use water, but that takes forever to evaporate and may leave behind contamination. Use the alcohol. The swab tips came out dirty and I kept changing them until the membrane looked clean and the swab came up clean.

As the inevitable saying goes: "Reassembly is the reverse of disassembly". When you are ready to put it all back together, bring the upside down keyboard assembly in front of you and position the membrane assembly over it and the plastic springs. Be sure that each "spring" is located properly and that the membrane lays flat on them. Place the steel plate in place over the membrane assembly and be sure that the screw holes, membrane, and steel plate all line up. Then start putting the screws back.

A word of caution here. Any/All of the screws involved DO NOT NEED TO BE TORQUED DOWN "DEATH GRIP TIGHT"! If you try, there are VERY high odds you will strip the plastic into which they are being threaded. You don't want to go there. Just turn them down snug enough to hold things in place.

You're almost done. Next replace the 30 some screws, and be sure that the little piece of white plastic that keeps the loop of the USB cord from does not fall out of place (the loop anchors the cord and provides strain relief where the cord is soldered to the circuit board). Then tip the keyboard assembly back into the base and reinstall the 3 Allen screws.

If you are lucky, you can plug the keyboard back in and all will be well. If you are still having problems with the keyboard, consider:

I was lucky - my daughter's keyboard appears to be working properly again! Good Luck!

- Harvey

Reference Links

Copyright ©2005 by The Mac Guild