Keyboard troubles

[vanpeebles]

Ah, try that first before anything too drastic

[Lardo Boffin]

This is getting more bizarre or at least irritating.

I flooded the Z key with cleaner and got it working with the multimeter no problems. Yay!

Plugged the keyboard back in and still the same:

Not working:

F2

SDFGHJ

The A key is now intermittent. Sometimes it works. Sometimes the wrong character is shown. Autorepeat does not work.

I took the keyboard out again. Some keys no longer worked when tested with the multimeter!

Got those going again. Plugged it in. Still the same but now number 2 is not working:

F2

2

SDFGHJ

Argh! Why do keys randomly stop working when tested with a multimeter? Is it a case of 30 years of crud working lose and causing an obstruction?

Do I need to desolder the whole thing in order to be able to clean each key? Not even sure I can do that without damaging something.

Anyone have a working keyboard for sale?

[Lardo Boffin]

Removed the keyboard again. Keys S and D now struggle for physical continuity.
Giving up for the night.

[sirmorris]

So It's the common connection for the 5 keys in a row that is one of the issues. Trace that out and see where it ends up. Unfortunately these switches are liable to give out, I remember stripping my kb down and cleaning it back in the day. It's possible but a pain in the ass. Keep on with the contact cleaner in the first instance.

[jltursan]

Try to reflow all the contacts related to these switches, sometimes cold solder joints could cause havoc.

[sirmorris]

Oxidisation on the connector too, perhaps.

[Lardo Boffin]

I have (at the moment at least) got connectivity via all the key switches using a multimeter. However I often find this and then the next day one or more keys don’t work. I assume this is the decades of crud settling again after being used for the first time in however long.

So while all were working I put the keyboard back in and keys sometimes work and sometimes don’t. But only the affected keys mentioned above. All the others are fine all the time.

If I unplug the keyboard and plug it in then the keys will sometimes work. I have tested the keyboard connector cable pin to pin and that is ok. I also tested from the keyboard pins to the other side of the connector ’ribbon’ and that seems fine. I have also checked most of the pins on the motherboard connector to the sound chip and the ones i can trace (which is most of them) are fine.

I have cleaned the keyboard and motherboard connector pins.

[sirmorris]

It's ghosts, then.

[Lardo Boffin]

It's ghosts, then.

Ah, ghosts in the machine.

[Lardo Boffin]

So I rebuilt my tatty over the weekend (soooo many screws! But nearly all the same size. Clever) in order to send it off to be fixed. I have checked and rechecked the keyboard and all seems well mechanically now. All keys have and seem to keep continuity via the multimeter test.

I thought that before I put it in a (large) box I would just give it a quick test. Because you never know.

I switched it on and pressed D (one of the dodgy keys) and amazingly a D appeared on the screen! This worked a few times. And then stopped. It became an underscore, or nothing or a lower case D.

While randomly pressing keys i found that if I press Del /Ins and then very quickly press D I get a D! This appears to be repeatable. Sometimes upper but mainly lowercase.

When I have some time tonight or tomorrow I will check to see if it is indeed still the same after being switched off.

So. Does this suggest maybe the keyboard controller chip? I have a games disc so I will boot some games to see if everything else seems to work.

The ghost in the machine returns...