>On Fri, 11 Sep 1998 Will Stephenson <[log in to unmask]> wrote
<snip>
>Once in a while (no discernable consistency), the keyboard
>stops working. Unplugging it and plugging it back in seems to reenergize it
>(strangely enough). We got a new keyboard from Dell, and though it seemed to
>happen less frequently for a while, it's doing it more again.

I go with the idea that the problem is in or around the keyboard connector,
and here are three levels of fault and fix, from easy to difficult.

1) dirty contacts: if the computer is in an area of industrial, traffic
or smoker pollution, the contacts could be coated with a thin layer of
tarry, corrosive goo. Since the keyboard connector is a cheap audio design
with small contact area and low contact pressure, removing and reinserting
the connector stirs the goo around but doesn't displace it much and it soon
creeps back between the contact surfaces. (This is consistent with your fault:
replace one of the contacts and things get better for a while.)

Cure: spray the plug and socket with "contact cleaner/lubricant"
(use an electronic grade 'safe on most plastics')
and gently insert and remove the plug a few times.
Then spray both again to flush and lubricate,
reconnect and see how long it lasts this time.
As the solvent dries dries, the trace of lubricant in the cleaner
is held in the contact area by capillary attraction and it
acts as a barrier to hold back the contamination.

2) dry or cracked solder joints: a 'dry' joint is one where the solder
didn't flow properly to wet the joint surfaces, often because of oxide
or grease from poor cleaning or fluxing. Because there is no metal alloy
layer bonding the contact surfaces, dry joints tend to become intermittent
as corrosion penetrates inside the joint. A cracked joint could be a dry
joint which has been mechanically stressed, or may just have been abused.
Sometimes the whole solder pad lifts off the board, necessitating
a wire link to reconnect to the track, but this isn't likely on a
through-plated hole multilayer motherboard. (I don't see how changing
the keyboard could have had much benefit here, except by accident.)

Cure: remove the motherboard completely and re-solder all the keyboard
connector pads using good quality electronic grade multicore solder and
a hot soldering iron. Rub the iron against the pins inside the solder
joint to make sure that any oxide layer is broken down, since you can't
inspect under the solder.

3) strained or damaged connector: if the computer has been badly handled
the contacts in the socket may have opened out. This is more likely on
a 5 pin DIN socket, since the mini-DIN PS/2 connectors usually just break!
(A new keyboard with clean, unworn plug pins could make better contact,
but I don't see why that should degrade again, unless someone regularly
swings on the keyboard cable.)

Cure: Inspect the socket closely to avoid unneccessary work.
On a 5-pin DIN socket you should just be able to see the forked contacts
and if these seem splayed open you might be able to probe beside them
and close the legs together again. Otherwise it's motherboard out
and a tricky (but quite do-able) desoldering job. Since the contacts
are in large solder-filled holes, desoldering is tough and you may
need to destroy the socket body by crushing or snipping then remove
the contacts one-at-a-time. Some sockets have a metal screening shell
to make life even more fun!

To decide which of these is more likely, it may help to judge how
the computer has lived. I think it's worth trying contact cleaner
first since it matches the symptoms and it's minimum effort.

If you have to open the case, it would be a good idea to press down
the keyboard BIOS chip to make sure it's properly seated in its socket.

Good luck!


Len Warner <[log in to unmask]> http://easyweb.easynet.co.uk/~len/ ICQ:10120933

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