Phantom key-presses on a Model M

[dacm]

Hi guys,

Recently bought a 2nd hand Model M, from 1989. It's connected through PS/2. (Using a PS/2 extension cable if that's relevant.) I've been getting phantom key-presses from it.

This means that sometimes when I press a single key I also get another register along with it. Sometimes on the press-down is registered on the `phantom' key. Which means that the same character is typed over and over. (I verified this by removing the cable once when it happened. - character kept appearing. Please flame if this is the wrong way to test this.)

This can even happen without me typing on the keyboard. The character that appears changes day by day. At first it was * then . now it is 2.

Any suggestions on debugging and/or fixing this issue would be hugely appreciated!

Thanks in advance,

dacm.

[iMav]

Can this be replicated on a different computer?  (with the same keyboard, obviously)

[dacm]

Haven't tried yet.

The problem seems to be intermittent so such a test would take some patience. Might hook it up to another box over night or something...

Will let you know what happens.

[itlnstln]

I would test low-hanging fruit first.  Get rid of the extension cable for awhile, and see if that helps. Then, try another PC.

[dacm]

I would test low-hanging fruit first.  Get rid of the extension cable for awhile, and see if that helps. Then, try another PC.

Just tried this.

Happens without the extension lead.

[dacm]

#1 cause of broken keyboards is liquid spills on the membrane.  If it occurs over multiple keys and isn't affected by key re-seating then that would be my guess.

Not an easy fix.  You'd have to do a nut/bolt mod.

It seems to happen on random keys. Sometimes it happens without any key being pressed.

Paid quite a bit for this keyboard... :-S

[Rajagra]

Please stop hotplugging devices in the PS/2 port, it isn't safe for the keyboard or the computer.

*, . and 2 look suspiciously like keys on the numpad that share a row or column of  the matrix. There may be something shorting somewhere. It could be that the ribbon cable leading to the controller is not perfectly aligned. Reseating the connection might fix it.

[dacm]

Please stop hotplugging devices in the PS/2 port, it isn't safe for the keyboard or the computer.

*, . and 2 look suspiciously like keys on the numpad that share a row or column of  the matrix. There may be something shorting somewhere. It could be that the ribbon cable leading to the controller is not perfectly aligned. Reseating the connection might fix it.

I didn't even know that hotplugging PS/2 was bad. Thanks for letting me know, I will be more careful in the future.

With regards to the numpad, this 'board also has some keys that do not always register, namely - + and all on the numpad. Could this be a related issue?

I've just bought a 5.5mm socket driver off ebay so once that arrives I will have to open this thing up and have a go. Bit scary though, took me ages to get hold of a model m. (This is a UK layout model. - 1391406)

PS: Why should I expect to see broken rivets? Do they just give way over the years? This 'board was disassembled and cleaned recently by the guy who sold this to me, so it should, at least, be clean in there!

[dacm]

Just opened up my model m and detached and reattached the larger ribbons.

Problem is still present. :-(

Took some pics will try to post those up when get a chance. - Maybe you guys will see something.

In the mean time, I'm wondering which ribbon does what. The smallest clearly just manages the LEDs. Do the other two do separate jobs? Which would handle the numpad? Basically I'm considering disconnecting one of the ribbons and deactivating the numpad to avoid the problem.

As always, any ideas would be hugely appreciated!

[002]

I had the same problem with mine when I got it.
It ended up being (as ripster mentioned) a problem with moisture/water left over on the membrane from when I cleaned the board.

HaaTa suggested I leave it overnight to dry and sure enough when I tried it the next day, I had no problems at all.

[dacm]

BTW, What is a `nut/bolt mod' Ripster? Can you point me in the direction of any relevent posts?

[itlnstln]

BTW, What is a `nut/bolt mod' Ripster? Can you point me in the direction of any relevent posts?

Check it.  The idea is to replace the brittle (and probably broken) plastic rivets with nuts/bolts.

[dacm]

Ok here are the pics please let me know if any of you notice anything dodgy! The background to this keyboard is that I bought it (not cheap IMHO) under the pretences that it was a 1989 model M in decent nick. (He'd picked a few model M's up second hand and had cleaned them up.) When I bought it I noticed that one of the numpad keys didn't always register so I knocked him down a tiny amount on the price. I think I've been had on this one!

(These were taken on my phone so please forgive the crappy quality!)


Took the top off.


Not sure if these numbers mean much!


Now this is worrying to me. The top image shows the sticker on the case with 1989 as the manufacture date. Fair enough, but the bottom image shows the sticker on the backplate. I've read that it's normal for the product number and year not to match up. But surely the back plate shouldn't have a manufacture date after the sticker on the case!

The guy who I bought this from said that he cleaned them up so surely he would have known about this.


The backplate has some rust...


I thought the big ribbon cable looked wonky but removing and reinserting made no difference. The end of the cable had some black greasy stuff on it and looked almost burnt at the contacts. Don't know if that's normal with these cables...


This was the state of the keyboard when I opened it. Not the cleanest. I don't even want to know what this stuff is. Makes me wonder if it was really cleaned before I purchased. (In which case he wouldn't know about the young backplate.)


Looked a lot better after I went over it with a toothbrush and some rubbing alcohol. (Still not spotless though.)


The top of the case has some clips broken off which is irritating. Annoyed that I didn't notice this when I purchased.


I think this is the problem though. Does this look right to you guys? Looks to me like there's liquid in the membrane. (As has been suggested as a cause of the problem. - Phantom Key Presses.)

Now it seems like doing the nut/bolt mod would fix this. (I would just dry the membrane sheets halfway through right?) But it sounds difficult and I really shouldn't have to do it considering that it was sold as being in great condition. (Water damaged != good IMHO.) I know where the guy lives so I could go and demand a refund. But it's a shame as I love my model m and uk layouts are hard to come by it seems...

Do you guys agree that water in the membrane is probably the cause of my trouble?

Thanks for taking a look!

[dacm]

Just to check that I'm not going mad...

The backplate and casing couldn't possibly be a pair (originally) right?

And am I right in thinking this devalues the keyboard?

[ch_123]

It's usually the case that the label on the back of the case will have the oldest date as it signifies when the keyboard was made. It's possible that this keyboard was refurbished at some point in it's life.

And that doesn't really devalue it at all. The fact that it probably has water damage does.