MX Keys Led Driver / No Backlight / IC Identification

[Kamynsky]

Hi Eeverybody
I'm working on fixing Logi(tech) Mx Keys ,
There is no back light on the keyboard .
I have measured Voltage going to LED's , 3,5V from "motherboard"
I have checked Led's there are starting to light up at 20V  , all of them light up when I've checked them with DMM one by one
My guess is that Led Driver have failed , but I'm unable to find Data Sheet for it any where (I guess I suck at searching for IC's)
Led Driver ? is SOT23-6 with designation W0122 3508A on the IC (Photo below)
Would appreciate help with identification , and maybe some ideas how to check if the issue is with the Led Driver
https://imgur.com/a/nL0NxKs

[fzabkar]

I expect that "508" is the date code (week 08 of 2005). Diode D4 has a date code of 0526.

It might help if you could trace the circuit around this IC, and measure the voltages on each pin.

[Kamynsky]

I found the IC
It is IS31BL3508A https://www.lumissil.com/assets/pdf/core/IS31BL3508A_DS.pdf
1.0MHZ BOOST CONVERTER WITH 38V INTERNAL MOSFET SWITCH

Unfortunately this IC is not available in my country and shipping from mouser makes no sense (cost more than keyboard I'm trying to fix )
I have found fallowing IC which seems to be good replacement for the original one AP3031KTR-G1 https://media.digikey.com/pdf/Data%20Sheets/Diodes%20PDFs/AP3031.pdf

Can some one please let me know if AP3031 will work pretty please !
 

[fzabkar]

The feedback voltage (FB) for the BCD part is 200mV, whereas the IS31BL3508A has an FB of 300mV.

If you measure the resistance between FB and ground, you should be able to work out the LED current (I = Vfb / Rfb). Then you could replace Rfb with Rfb x 2/3, or add a second resistor with a value of 2 x Rfb in parallel, to get the same current with the BCD part. The dimming function might need closer examination, though.

You should check the ENable pin to confirm that the chip is being turned on.

[Kamynsky]

Thank you ,
Will search a little bit more for more similar IC ,
Will check all lines with Oscilloscope since now I know what they are doing and what I should see on them  (time to learn using Oscilloscope )
Once I have it running , will post what IC I've used and what had to do since this is quiet popular issue with this keyboard, maybe some one will use this knowledge