PCB acting funny, help needed

[dabeshu]

So, my PCB is fritzing and I’m new to this so I need some help.

The F1 (second switch from top right), 1, Q and A keys aren’t registering properly. I used a metal tweezers to check for connections on the leads, I tested the switches to see whether or not they are working, and both of these aspects test out alright.

When soldered to the board, the switches don’t register, and using the tweezers while they’re in there results in nothing. There’s this little breakout board that goes into that black slot thing adjacent to where F1 is, and while desoldering the old switches I had to remove it. It seemed like I put it back in properly and I don’t know if that might affect the functioning of the connections, but maybe I didn’t put it in correctly when inserting.

Anyone have an idea of what might be going on here? Hoping I didn’t make this thing a paper weight. Thank you

[suicidal_orange]

I see a lot of what looks to be solder splatter, including some on the pins of the black connector - that can't be good and needs cleaning off.

You can see the diodes connecting across the board so it makes sense to lose a whole column as you have but there's a slight problem as Q is (or at least should be) directly to the controller chip.  If shorting the left pins of the dead switches to the right pin of Q doesn't type the right thing you are looking at soldering to the chip.  You're lucky that it's on the corner or it would be even harder.

If that makes no sense let me know and I'll add some coloured dots when I get home, if no-one beats me to it

[dabeshu]

Yeah if you could explain it in more detail I’d really appreciate it!

What would be the proper output if I do that? Would it just be whatever character the dead switch is?

Should I desolder the switches? I’m clueless so I don’t want to touch anything until I know what’s wrong and how to test/fix

[Darthbaggins]

As Orange mentioned, I would clean up the splatter on the pcb and clean up some of those solder points - some don't look complete/clean which would cause a bad connection.

[dabeshu]

What should I use to do that? Should I desolder the switches first?

[yui]

try to brush it off gently 1st, solder that lend where it should not be is often too cold to stick properly. and if you have not done anything to that daughter-board you have at least for sure not damaged the controller, as the chip on the photo is just an IO extender (PH424A) for RGB and rows (hoping it can help SO). only thing i would also try to do is to clean the contacts in the connector and the edge of the board, from what i can see to me it looks like columns go directly to it.

still rather strange to use a m.2 connector for the controller, i may very well be wrong, but looks like it would be it to me.

and if you tested your switches with a multimeter it could also be too slow to see a chatter in the switch, that maybe the controller could filter it out but the chance of all the switches in a column to be dead are rather slim.

[dabeshu]

Would 70% isopropyl alcohol with a tooth brush be okay? Do I need to desolder? Thank you

[suicidal_orange]

I'm assuming the designer of this PCB was friendly as the diodes are interestingly numbered which hopefully corresponds to the columns.  The purple pin doesn't look to have any solder on it, but that could just be the angle of the picture.  If it has none add some, if it has some but doesn't look like it the pad is probably damaged which will be found/fixed in due course.



Shorting pale green dots to the blue dot will bypass the switches of the dead positions, whichever green you started from is the character that should be typed.  I think the bright green keys will also work shorted to blue but maybe might not (commercial boards can be very strange and the IO expander makes it look like one...)  This might be hard if the daughterboard covers the blue pin so you might need to solder a long wire to the blue pin and move the other end.  If green-blue doesn't work check the diode for that switch (orange bar) to blue.  If that works you need to solder a little wire between the end of the diode (orange) and the green switch pin, then test the switch again.  If the switch still doesn't work you need to solder a wire between yellow or purple and blue.

If nothing types while doing this it's possible the break is between the blue dot and the pin on the chip with a yellow arrow pointing to it, but I'm pretty sure that's still connected otherwise more keys wouldn't work.

Would 70% isopropyl alcohol with a tooth brush be okay? Do I need to desolder? Thank you

Sounds good, desoldering can only cause more damage so please don't

[dabeshu]

I'm not getting output from any of that unfortunately. At this point I'm thinking of finding a professional to hire if there's nothing more I can do

[dabeshu]

But wait I’m supposed to use the tweezers on the diodes? I was doing the sockets. Not sure I’m doing it right

[Maledicted]

Would 70% isopropyl alcohol with a tooth brush be okay? Do I need to desolder? Thank you

I maintain student Chromebooks for a living, which end up exposed to anything you can imagine, like bananas, yogurt, milk, soup, etc. I have run entire motherboards under a faucet if they're bad enough. The important thing is being absolutely sure there are no shorts by the time you try to apply power. I use 70% Isopropyl (the higher the better though if you're in a hurry, it won't hurt the PCB) and a toothbrush frequently for removing corrosion. It works great for cleaning PCBs without damaging them.

It does appear he's suggesting trying to short directly between the orange ends of the diodes he marked to the switch leg he marked in blue, yeah.

[suicidal_orange]

But wait I’m supposed to use the tweezers on the diodes? I was doing the sockets. Not sure I’m doing it right

The left pin sockets should be connected to the diodes, if that connection got damaged when you resoldered it wont work (and still wont if you desolder the switch again)

You need to touch one end of something conductive to the blue switch pin and the other end to the green pin or the end of the diode.  Scissors can work at this range if they're pointy enough but tweezers wont reach.  A piece of wire is safer for your fingers and easier to get both ends where you want them.

If nothing types you need to go to the little leg on the corner of the chip with the yellow arrow instead of the blue pin.  Someone recently managed to solder to a pin in the middle of a chip when a professional repair place said they couldn't do it - I was surprised and impressed.

[dabeshu]

All I had to do was put some tape over the pins of the switch that sit under the daughter board which is apparently a common issue. Thanks for all your help though! I really appreciate this awesome forum