Dell CPX keyboard problem-duplicate keys

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Hi, I have a Dell Latitude CPx notebook with a keyboard problem:

It has  worked well for many years, but some months ago, it started typing
more than one letter

for each key pressure. This problem has become worse, now it's boring to
write something, I

musst always stay there do delete duplicate characters.
I obviously checked the related  windows options in the control panel, but
this seems to be an

hardware problem.
I also noticed that now CTRL and Shift keys work only if I press them very
hard .
When the laptop is turned on for many hours, it is still worse.

so I replaced the keyboard, but the problem came again after a couple of

I tried to disassemble and reassemble the notebook many and many times,
tried both the old and

the new keyboard but nothing has changed. The keyboard's connector are in
good state.

I don't know what to do, I start thinking that this could be a mainboard
fault, what could I do?

Thanks for the answers.

Re: Dell CPX keyboard problem-duplicate keys

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Since you have had the system apart more than once it should have had the
dust cleaned out already.  You might want to verify the cooling fan is still
working properly as well.

I have seen computers exhibit this problem after an update loads or replaces
a keyboard driver with an incorrect version.

To identify if your problem is hardware or operating system (driver) you
need to get your hands on a diagnostics boot CD that people usually use to
inspect or repair a defective hard drive and see if your keyboard problems
go away while you are using it.  If they do then your problem is most likely
the keyboard driver on your windows installation and not the hardware
itself.  A couple of examples I like to use is:
Ultimate Boot CD at or one of the UNIX or Linux boot
CD's.  You might even try booting from your Windows CD and see how the
keyboard responds after it loads.

Running a memory testing program like Memtest86, check the "Free Download"
section at might also show a possible problem.  Reseating
the memory might "fix" the problem as well if the memory problem is simply
connection related.

Re: Dell CPX keyboard problem-duplicate keys

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Hi, thank you for your message.
The laptop is clean, I take over dust each time I open it; the cooling fan
is working properly.

I tried also with different operating systems, (dos, linux) , but I get no

Now I'm trying a full memory test , I will let you know.

Thanks for the help

Re: Dell CPX keyboard problem-duplicate keys

P wrote:
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If the symptoms are identical, it's likely that your keyboard is ok.
If they're just similar, you might have two bad keyboards.

I had a similar problem with a cpxj keyboard.  Replacing keyboard fixed
it so I never went further with the diagnosis.

This is often caused by some high resistance between the interconnect
pins.  I've seen bad scanner chips with internal shorts.
I've seen dirty connectors with gunk in the connector.
I've seen what looked like pencil marks on the flexible cable shorting
I've seen gunk in the keyboard shorting traces under the keys.

Not much can be done about the bad chips...except cleaning the board if
it's external to the chip.  If you look at the signals on the receiver
pins as you press keys, you can see if two signals are present and
where.  I once put a pullup on a chip pin to counteract a high-resistance
short.  Worked for a while, but broke again.

You can clean ribbon sockets with some paper dipped in alcohol.  Use the
heavy bond high-cotton paper cut to the right width.  Don't wanna leave
paper fibers in there.

You can clean the flexible cable, but have to be careful not to wipe off
the needed part of the carbon conductors.  Conversely, if the conductors
are "weak", you can sometimes build them up with a pencil.

I once fixed a bad keyboard with a stun-gun.  Let it arc between
conductors and it burned out whatever was shorting.  Obviously won't
work if there's any electonics in there.

Most keyboards come apart rather easily.  You can clean between the
layers, let it dry and reassemble.  Reassembly is VERY difficult without
the proper press...keyboard construction varies widely. YMMV.

Sometimes a thorough cleaning of the motherboard fixes all manner of
ills.  But it's a last resort.

Return address is VALID!

Re: Dell CPX keyboard problem-duplicate keys

Have you tried an EXTERNAL keyboard ? Cost $10 (CompUSA, Best Buy) and if
IT fails too then you are SURE it's not a physical issue - rather a logic
problem. Especially since you say that it gets worse the longer you use
it - sounds heat related rather than keys sticking.

If external works, is that acceptable ?  Can still use as desktop PC.
Beats tossing it in the trash.

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Re: Dell CPX keyboard problem-duplicate keys

I just tried an external keyboard, with that I don't have that problem.
I had already looked at the ribbon connector, but it is completely covered
by plastics, and the end of the flexible cable is fixed on a plastic
connector with pins, so it can't be damaged at that point.

I tried to completely disassemble one of the two keyboard, without finding
any dust,  I reassembled it and the problem is still here, but something has
changed: now the space key repeats itself more than before (each pressure
give at least 2-3 space characters) and the other keys repeats a little
less. I still need to press extremely hard ctrl and shift to use them.
I still notice that with the cold notebook it works a little better.

I tried to drop a little the keyboard and/or to toggle some keyboard screws,
something changes (some keys works better some worse) but I'm unable to get
it work perfectly.
I tried to drop it up at the ctrl corner and now I don't need to force it,
but I think it won't do for much time.

I don't know what else to do.
It's a pity because it's a good notebbok, with 2 good batteries...

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Re: Dell CPX keyboard problem-duplicate keys

P wrote:
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Your problem is unlikely visible "dust"
Clean with alcohol BETWEEN the layers where the contacts are.
Can you see any crosstalk between the pins when you look at it with a

Re: Dell CPX keyboard problem-duplicate keys

<<snipped..... <kinda works > >>
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It might just be that as it's getting older the little rubber cushions
under (both) of the keyboard are drying up and no longer 'like new'. If
you REALLY want to salvage it, and since you said that you already took
one all apart .... note a few keys that are sticky.
Pop off the keycap carefully and remove the 'cushions' or springs -
whatever makes them 'springy'. Lightly wet a Qtip and clean under the
keycap - just a bit - you want to only affect that ONE keycap for this
test. Clean the cushions in soapy water to remove built-up crud. After all
is dry put those cushions/keycaps back on there.
Are they OK now ? YES = crud build-up is the problem ( not uncommon on
older keyboards) . If NO,  then either the cushions have lost their spring
or not a physical issue and you're back to where you are now - except that
you KNOW playing with the kays themseleves won't help.
Good luck.

Maybe just pack the external keyboard along with the laptop - still

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