Some switches aren't registering

[chyros]

Got a new keyboard this week and a bunch of keys aren't working, or not working very well. Specifically, num 4, 5, 6, 3, end, A, J, K, ;, Z, C, <, ?, and right shift. The board is pretty old though, and the connector is a bit dirty:



The soldering also looaks somewhat weird, but not specifically around the switches that are dodgy. I don't think I can open the switches to look inside.

What kind of problem does this sound like? Connector, soldering, or switches? I'm not sure why it's these specifically. Anyone have any idea?

[suicidal_orange]

That sounds like a break (or more likely multiple breaks) in the switch matrix - all those keys are connected to one or more of the others.  If you think the soldering on a switch looks dodgy reflow it with some fresh solder or flux and see if that helps, you may be surprised.

If that doesn't fix it you'll need to work out what should be connected but isn't - do you have a multimeter or a continuity tester?

Taking some pics of the PCB from an angle where the traces can be seen (see this thread for some good examples by berserkfan) is the best way to get help on where the problem may be, if not the model of the keyboard so pics may be searched for

[chyros]

Cheers mate, I'll borrow a multimeter next week, I need to do something else with it anyway.

Here's a picture of part of the PCB:



Most of the weird soldering seems to be concentrated around the area with the controllers in. It almost looks like a newbie soldered them in. Some solder points are connected by the solder; either in areas that seem to be connected by traces anyway (1 & 2; I would imagine this doesn't matter?), where traces go into opposite directions (3 & 4), and where I seriously have no idea what's supposed to go where (5 & 6). Any ideas on what's supposed to be connected to what?

[suicidal_orange]

Looks random and I have no idea what's going on there especially without seeing what's on the other side, but if things are connected where they shouldn't be you get extra keys being "pressed" not keys not working, so we'll assume it's ok.

The problem should be between the switches which are working and those nearby that should be connected to them but aren't.  You have so many not working you'd probably do better taking a pic of the whole board, if you can!

Also I forgot to ask - have you tried shorting the two pins of the non-working switches with something (a piece of wire, scissors, tweezers...) and seeing if that registers a keypress with the computer?  I've assumed it's the matrix as there are lots of switches out but there's a small chance it isn't.

[chyros]

Ah so you mean I boot up the computer with the keyboard connected and then connect the two pins with something, say, a pair of tweezers? I'll try that, thanks .

[chyros]

Tried it; connecting the pins with a pair of tweezers makes it possible to trip every single one. Does that mean it has to be the switches, or could it be something else?

I also tried several adapters and an active converter btw, so it can't be the adapter, I'd think.

[suicidal_orange]

Wow, that is a surprise!  All the switch does is short the two pins so if shorting them manually works it's definitely the switches at fault.  You can try blowing some compressed air into them in case it's dirt but other than that it's time to get out your desoldering pump so you can open them up for inspection and probable replacement.

What board is it?