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Old 06-03-2012, 02:37 AM   #1
RandomTroll
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12 keys no longer work


The keyboard on my laptop (eMachines e725, 15-inch screen) started misbehaving Friday night. First the x key would happen repeatedly, then the c, then the s. I could get this to stop by pressing the repeating key usually. I tried cleaning with the edge of a small piece of a 3x5 card, which got out almost nothing, and compressed air. I use a wireless keyboard at home, which is most of the time I use the computer, and keep a clean unused handkerchief lying on top of the laptop's keyboard. The wireless keyboard works properly.

Then it got worse: when I booted the computer wailed just after posting the eMachines logo and offered the opportunity to run setup or choose a different boot device. I turned it off and upside down (but slightly open) for the night. Saturday morning it no longer wailed or had stuck keys, but the ESC ~ F1 2 4 5 7 0 = i o ctrl(left) keys no longer work. I can use the numeric keyboard for the numbers and, at the command line, compose the ~ i o = characters with the alt key. This is inconvenient and slow - and it doesn't work in X (why not?).

A few hours before this behavior began I spilled a cup of water on the table the computer occupies, behind it. I immediately propped it up on a couple of pens next to it, cleaned up the spill, turned it off, and looked at its bottom. I didn't see any sign that it had gotten wet. No water got on top of the keyboard. If the whole keyboard had failed I could imagine that I had somehow damaged some component that supported the keyboard (perhaps the fan was on, sucked up some water and sprayed it inside) but 12 keys of no apparent relation - I don't see how to correlate that with anything other than damage directly to the keyboard, traditionally a spill or accumulated gunk, but that didn't happen.

Any ideas?
 
Old 06-03-2012, 04:18 AM   #2
Zilvermeeuw
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A keyboard has a 'wire' grid. That means, several keys are connected togetcher to the same 'wire'. If only that wire is misbehaving, all keys connected to that wire are misbehaving.

Try removing the keyboard and check the connection of the keyboard to the motherboard.
 
Old 06-03-2012, 06:14 PM   #3
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Quote:
Originally Posted by Zilvermeeuw View Post
A keyboard has a 'wire' grid. That means, several keys are connected together to the same 'wire'. If only that wire is misbehaving, all keys connected to that wire are misbehaving.
I have taken apart a few keyboards so I know this. The dysfunctional keys are on 4 different wires.


Quote:
Originally Posted by Zilvermeeuw View Post
Try removing the keyboard and check the connection of the keyboard to the motherboard.
It's a laptop, which makes removing the keyboard difficult, especially since Acer doesn't publish the technical manual explaining how to do it. Previously I owned Thinkpads; IBM published the manuals for their computers. Getting to the keyboard required taking everything else off first: first the screen, then all the stuff underneath the keyboard: it's a big deal. I'd hate to do it without a manual.
 
Old 06-03-2012, 09:36 PM   #4
frankbell
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If you go to YouTube and search for "emachines remove keyboard," there are a number of tutorials. A quick look did not show one for the 725, but there's one for the 625.
 
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Old 06-03-2012, 11:35 PM   #5
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Quote:
Originally Posted by frankbell View Post
If you go to YouTube and search for "emachines remove keyboard," there are a number of tutorials. A quick look did not show one for the 725, but there's one for the 625.
That's just an ad. But it's a good idea: I don't usually think of YouTube: there seem to be some useful videos there.

My real question is what else could be going on. I use the laptop's keyboard rarely, only when I take it from home, once or twice a week for an hour or two usually. I haven't spilled anything on it or dropped anything on it or hurt it in any way. I keep a cloth over it at home to keep dust from collecting. I have cleaned the dysfunctional keys thoroughly and can't get anything out. Their action feels just like all the working keys.

What else could have failed? The only parts of the underside of the computer exposed are the hard drive and ram, which both test okay, and the fan. I haven't found a way to query the fan's status but the temperature stays within bounds. If the fan sucked up some spilled water and sprayed it inside what would it have hurt that would cause these symptoms? The keyboard has a foil layer on its bottom: I don't see how a little water would hurt only a few keys. The original PC had a discrete keyboard controller chip, the 8042. This computer, most IBM-type PCs, has the 8042's hardware but it's integrated into a large chip that provides all kinds of functions. I'd hate to replace the keyboard and have that not be the problem.

Last edited by RandomTroll; 06-04-2012 at 12:27 AM.
 
Old 06-04-2012, 02:52 AM   #6
Zilvermeeuw
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I have seen this behaviour on 'wired' keyboards before. All of them had some oxidation at the connection between the foil layer and the pcb connector. One had oxidation on the foil layer, near one key. This last oxidation disconnected the complete wire, which caused several keys to malfunction.

I think removing and cleaning (or replacing) the foil is the only solution.
 
Old 06-04-2012, 06:30 AM   #7
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Quote:
Originally Posted by Zilvermeeuw View Post
I have seen this behaviour on 'wired' keyboards before. All of them had some oxidation at the connection between the foil layer and the pcb connector. One had oxidation on the foil layer, near one key. This last oxidation disconnected the complete wire, which caused several keys to malfunction.
I don't understand this. All the keyboards I have used have had 3 layers: one that had traces that ran horizontally, one that ran vertically, and a layer in between those 2 that has no conductors and holes where key contacts are: when one presses a key a contact gets made between one row and one column which a chip interprets as a location on the grid and sends the associated keycode. If a column or row fails then every key after that one doesn't work. In my case in the second row the ~ 2 4 5 8 0 = keys fail but the 1 3 6 7 9 - backspace work; in the third row the i and o fail but the rest work.

The foil layer has always been mechanical and electrical protection, not an active part of the circuit. (Keyboards not in laptops don't have it.) For it to matter the insulation on the lower conducting layer would have to rub through - which probably would make the key fail. But it's aluminum: why would it oxidize further? And why would it rub through, I having used it so little, especially the ~ ?
 
Old 06-04-2012, 07:09 AM   #8
Zilvermeeuw
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The grid is not always nicely in order, as you think is logical. Therefor sometimes it looks like random keys and not nicely in line.

The foil layers are NOT always protected. Sometimes it's just two foils. Nothing more.

The aluminum is well protected by its oxidation. But on certain places, its not aluminum. Like the place, where the other foil must connect, if a key is pressed. And the connections to the main board. These are the places, where your keyboard is broken now.
 
  


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