Working on a MBP 820-3115-B without keyboard backlight. The board has another issue, it will produce a 3 beep RAM error if the bottom RAM slot is populated. It boots and works fine with a single RAM module installed in the top slot. Even though a faulty bottom RAM slot is a fairly common issue on this model (the legs of the RAM slot detach from the board, but I checked them on my board and they're solid), I believe the 2 issues might be related. After checking the schematics, I noticed that R5852 is completely missing from the board. There are some very faint signs of corrosion in the area, but from the look of it, it seems like this component was never installed (for the record, it's a 10k size 402 5% resistor). According to the schematics this component connects to both SMC_SYS_KBDLED and to pin 174 (MEM_B_DQ<55) of the bottom RAM slot. I probed around and all values of components on the KB backlight circuit seem perfectly fine, no shorts or anything. I'm planning to source a replacement and (re-)install the resistor, I'm just trying to confirm that this has the potential to fix the issue. Also, if anyone has experienced a similar issue, feel free to let me know how you solved it