A4000 keyboard dead keys

[TheBilgeRat]

So I finally got my A4000 out from the move and fired it up. Its been a couple of years and its been sitting in a box in the attic. I found that the top row of keys (escape key through F8) do not work. However, F9 and F10 work fine as do all the other keys. I ordered some silver paint and cleaned off the pads with qtips and distilled water and let it thoroughly dry before reassembly. There is no obvious damage to any traces.

Has anyone else encountered such behavior? Its weird that the keys affected are horizontal and only partial along that line. Any other recommendations as to what could be the problem are appreciated.

[Jope]

It could be a break in the matrix between F8 and F9. Check http://eab.abime.net/showthread.php?t=81893 for a PDF of the keyboard matrix, it is the same for the 4000.

[alexh]

You can buy replacement keyboard membranes for A4000 (which I believe is the same as A500) in UK they are £29 which is pretty expensive but cheaper than new keyboard.

[Jope]

This will work for a very late model A4000 keyboard. The majority were PCB based.

A rough way to distinguish: metal springs, linear feel = membrane and rubber cups, clicky feel = PCB.

[TheBilgeRat]

Thanks all! Definitely a membrane based board - I've had it a part a few times looking for obvious signs of damage. I'll look for one of those membranes for replacement if all else fails. I sure would love it if someone made a drop in mechanical board for these

[nogginthenog]

I would try cleaning the membrane contacts with 99% isopropyl alcohol and a cotton bud.

[TheBilgeRat]

Originally Posted by nogginthenog

I would try cleaning the membrane contacts with 99% isopropyl alcohol and a cotton bud.

Tried that - no dice. They all were pretty dirty but the dead keys stayed dead. I'll probably try checking with a multimeter next to see if it's traces or the keys themselves

[Jope]

The membrane paint can dissolve in IPA, better just use a damp paper towel and quickly dry it afterwards with a dry paper towel.

[TheBilgeRat]

Originally Posted by Jope

It could be a break in the matrix between F8 and F9. Check http://eab.abime.net/showthread.php?t=81893 for a PDF of the keyboard matrix, it is the same for the 4000.

This was it. Spot on. I had it apart several times and didn't see anything even under magnification...From the top. Got the multimeter out and verified there had to be a break between f8 and f9 and there was. When I flipped the matrix over I could see the break with magnification. Attempting to use some caikote to repair but I think a new matrix is in order. There was no visible "scratch" or anything to have caused the break so I think this matrix is just hitting the wall on its shelf life.