Faulty LEDs in Mechanical Keyboard's Left Column

[ricardodacp]

The left column of this keyboard has faulty LEDs: esc, tab, capslock and ctrl stuck on color red and shift does not turn on at all, but all the keys work fine.
 

I'm assuming it's water damage, particularly considering the state of the shift LED.

My question is, if I replace the faulty LEDs, would that resolve the issue? Or is it possible that there's additional damage to the board itself?

 

Thank you!

 

Edit: uploaded second image with power to the board and LED's set to OFF.

[Drevo Dano]

It does look like water damage. If the main IC doesn't appear to have water damage then yes replacing the LEDs should solve your problem. Just make sure to clean it well with isopropyl alcohol after removing them. You may also have to replace the resistors for the LEDs if replacing the LEDs doesn't work. They look fine on the pictures however

[Simon Hosa]

I think that resistors should be fine. It is only a passive component, but I am worried about transistors which can be easily damaged in water.  

[mariushm]

Replacing leds won't solve the problem.

The led is turned on, which means it either receives power, or the ground is connected to ground all the time when it shouldn't.

 

A microcontroller has two ways of turning on a led.

1. The ground (negative) of a led is connected permanently to ground, and the microcontroller or led driver sends power to the anode (positive) of the led to turn it on.

2.  The positive of the led is always connected to power and the negative is connected to the driver or to a transistor or mosfet that acts like a switch - the led turns on when the "switch" is turned on, or the driver connects the negative pin to ground. 

 

The 2nd mode is more common.  So in this case, it's possible the water caused something to become conductive, maybe a transistor is now permanently on because electricity can flow through residue from water into the transistor base pin and keep it turned on. Basically, you have a on-off switch stuck in the on position.

 

Check those 3 pin components q2, q4,q7,q10  etc all those q parts are transistors or mosfets, on-off switches... use isopropyl alcohol or other things (acetone would work, nail polish remover, but keep it away from plastic of the leds as it could eat the plastic)  and clean the area around their pins. Clean the leads of leds some look corroded.

 

Use some cotton swabs or regular cotton wool wrapped around some wood sticks or tiny screwdrivers, dabbed in isopropyl alcohol or acetone or other solvent and clean residue off the board, anywhere you see some discoloration wipe it.

 

 

[Simon Hosa]

Mariushm exactly, but I personally think that it will be an array created by PNP and NPN transistors. This is more common for keyboards to reduce the amount of IO pins.  And also there are PNP transistors (driven by NPN)  according to the datasheets below. So it looks like the rows are driven by PNP and columns will be driven by NPN. It means that both transistors in the fourth row should be changed, and also NPN transistors for columns. Can you please take a photo of the whole PCB from both sides, and then a few details? 

 

https://html.alldatasheet.net/html-marking/1133446/SHENZHENSLS/SLS3401/846/1/SLS3401.html

 

https://pdf1.alldatasheet.com/datasheet-pdf/view/140113/AVICTEK/1AM.html

 

Good message for you is that these are standard and cheap transistors. If you show these datasheets in some shop with electrical parts they'll give you an alternative transistors.