Tatung Computer Forum

Ah, try that first before anything too drastic

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?

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

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.

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

Oxidisation on the connector too, perhaps.

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.

It's ghosts, then.

sirmorris wrote: ↑Sun Nov 10, 2019 5:49 pm It's ghosts, then.

Ah, ghosts in the machine.

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...