Please help with a CPC664 keyboard

angelcaio · 18:09, 28 April 20

I have a problem with a keyboard on a CPC664. I tell the story:
Among other problems with the floppy drive, power switch, housing, ... The membrane was missing and I bought one online. All the keys worked except for the space bar, this key got stuck a little.
I sprayed the space bar spring with WD40 without removing the membrane and the key.
Now the space bar, the [\] key the M key and the [Control] key fail (all at the bottom of the keyboard and most likely also received WD40)
I checked the membrane after repairing it with conductive ink because some tracks broke when I connected it and it was fine.
I measured the continuity in the key contacts when pressed (without membrane) and there was continuity in all of them, but in those that did not work, the resistance value measured by the multimeter was ten times greater than in the other keys: the keys [\] the M key and the [Control] key that did work before. This did not happen suddenly, but they gradually failed.

The keys (and the membrane) are different from those of the 6128 and 464.
They fit into a kind of plastic tube wrapped in a spring and on the bottom it fits into another piece of plastic. From inside the tube, when you press the key, a kind of piston with two contacts appears. The circuit is closed by pressing the key and lowering the plunger. Attached photos

Could they have been damaged by the WD40?
i can fix it?
Thanks in advance and sorry for my horrible english.

Bryce · 18:44, 28 April 20

The WD-40 didn't damage them, it just coated them in a layer of crap. Wipe the membrane down with a wet cloth and dry it with some kitchen paper and they'll work again.

Bryce.

angelcaio · 19:06, 28 April 20

Quote from: Bryce on 18:44, 28 April 20
The WD-40 didn't damage them, it just coated them in a layer of crap. Wipe the membrane down with a wet cloth and dry it with some kitchen paper and they'll work again.

Bryce.

Thank you Bryce, but I already cleaned the membrane with distilled water and checking with the multimeter it is apparently ok. It worries me the values when measuring the contacts on the side of the keys and I don't know how I can clean them. Could isopropanol work?

Bryce · 21:09, 28 April 20

Then it's coated the carbon pad on the key. Put some isopropanol on a cotton bud and give them a clean.

Bryce.

angelcaio · 07:19, 29 April 20

Quote from: Bryce on 21:09, 28 April 20
Then it's coated the carbon pad on the key. Put some isopropanol on a cotton bud and give them a clean.

Bryce.

Many thabks Bryce. I'm going to look for isopropanol then

Bryce · 08:35, 29 April 20

Bad time to be looking for Isopropanol as it's the main ingerdient of hand santiser products. It should cost around €9 for a litre, but I've seen it being sold for 4x that price recently.

Bryce.

angelcaio · 11:51, 01 May 20

Hi, I have cleaned it with 99.9% isopropyl alcohol and I have waited for it to dry for an hour and a half, but it remains the same: there is continuity but the multimeter returns values between 500 and 600 (on the keys that work the multimeter shows around 60 or 70).
Can I try something else?
Thanks

Bryce · 12:12, 01 May 20

Yes, use some very fine sandpaper to remove the top layer of the rubber conductors. The WD40 must have reacted with the rubber and formed some coating that the Isoproponal can't remove.

Bryce.

angelcaio · 16:34, 01 May 20

I I have used a p2500 sandpaper, it has worn a little, but still gives the same high values.

Bryce · 18:52, 01 May 20

Really wierd, the WD40 must have dried it out and caused micro-cracks or something. I'll check my stock and see if I have some replacement parts for you.

Bryce.

angelcaio · 22:01, 01 May 20

That would be great. Thank you very much Bryce

Bryce · 08:32, 02 May 20

Extremely annoying. I threw them away a few weeks ago when I was trying to make space. It doesn't look like I kept any of them. You'll have to find a computer that used similar keys. I think the EuroPCs had these keys too.

Bryce.

angelcaio · 09:46, 02 May 20

Thanks anyway Bryce.
I don't know if this is a good idea but I can borrow the conductive ink pen again. If I paint the entire area indicated in the photograph, when points A and B make contact with the membrane, I should close the circuit, is that correct?

Bryce · 12:27, 02 May 20

It wouldn't do any harm to paint the entire bottom surface, ie: the surface between A and B too.

Bryce.

angelcaio · 15:17, 30 May 20

Quote from: Bryce on 12:27, 02 May 20
It wouldn't do any harm to paint the entire bottom surface, ie: the surface between A and B too.

Bryce.

I finally painted a small piece of adhesive with conductive ink and attached it to the part of the key that makes contact with the membrane. But I had to buy another membrane because the first one practically fell apart. (I got a refund for this, no problem) but it took me a long time to decide to buy another membrane due to possible shipping problems for the covid 19 and it also took several weeks for this one to arrive. Now, finally, it works fine.
Many thanks for the support.

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Please help with a CPC664 keyboard