Repeating key

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Compaq Presario 2504EU has a constantly repeating u key. I've removed
the key top and the scaffold thing below so that I can lift the rubber
and get to the contact below. I've cleaned the contact area and rubber
with iso propyl alcohol and the key stops repeating. However once it
dries it starts to repeat again.

It also has a problem with the drive interface, it will only run in PIO
mode (following a close lightening strike) so is very slow. I don't
think it's not worth replacing the keyboard.

Any suggestions or ideas?

Faster, cheaper, quieter than HS2
and built in 5 years;
UKUltraspeed <

Re: Repeating key

Rodney Pont wrote:
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Drives can be down-shifted into PIO transfer mode,
as a means to "restore reliability" to the interface.
The idea is, if a drive is throwing CRC errors,
the Windows driver slows it down, thinking the read
error rate will be reduced.

This is a concept copied from Unix, which does
the same thing for SCSI devices.

They have a "Fixit" file here, for that. As well
as some Regedit you can try.;en-us;817472

Depending on your luck, that might be easy to fix.


I don't have a solution for the keyboard. Keyboards are
relatively high impedance circuits. The keyboard I built
as a hobbyist, from scratch, the scan matrix used 100K
impedance signals. A bit of surface leakage, might cause
a key depression to be detected. And being a scan matrix,
more than one key sits on a scan line. Some keyboard
chips used a 17x7 matrix of row and column lines.
Pulses go out on one set of lines (each line is pulsed
one at a time), and the detection lines look for the pulses
as proof one of their keys have been pressed. I don't know
how I could "condition" the signals, to stop a problem
from showing. Even if you drilled out the two pins
or connections to a row and a column line, the leakage
could be elsewhere underneath the keys. Like, carbon
scoring from an arc or something. You'd think if that
happened, the keyboard chip would have burned out...

You could clean the entire keyboard PCB, but that would
be "above and beyond the call of duty". Maybe someone
will have parted out a similar machine on Ebay, and
you can get another keyboard there. On some laptops,
there are four or more different part numbers for keyboards,
so you have to be very careful, to get exactly the
right one for your machine. Each part number, would come
with a different set of keycaps and relevant encodings.
(Like a German or French keyboard maybe.)


Re: Repeating key

On Sat, 26 Oct 2013 03:33:45 -0400, Paul wrote:

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I've reset the mode several times and tried different chipset drivers
but it always switches back to pio mode. The drive itself works
perfectly in another system so I've given up on trying to fix this.

Quoted text here. Click to load it

I don't have the enthusiasm for stripping this laptop down. I had to
change a small fan in the back a couple of years ago and it was very
involved. I was surprised that liquid on the contacts stopped the
repeating of the key though, I would have expected it to do the

Thanks for your reply but I think this one has reached it's end of

Faster, cheaper, quieter than HS2
and built in 5 years;
UKUltraspeed <

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