Replacing backlight fuse on t420s

by epilys on 2019-04-19

It is on the upper left of the monitor connection, testing the local fuses with a multimeter led to it quickly.

time for the dirtiest repair job ever. I have never done tiny SMD soldering in my life. I had no flux, small solder or a fine soldering tip and they are expensive to get in this forsaken part of the world. I usually order stuff online but I didn’t want to wait.

I ordered 5 fuses (for redundancy) from digi-key with express shipping and they arrived in 2 days. It was only afterwards that I realised I could have ordered solder, tips and flux from digikey as well.

I needed to protect the laptop from ESD. I am far from the actual ground (1st floor) so I connected the

on my oscilloscope.

The fuse is 0402, ie 0.4mm x 0.2mm. Smaller than a flea, and

it looks like a breadcrumb unless you look at it with a magnifying lens.

Removing the old fuse was out of the question because a safer way exists: applying the new one over the old one. By the way, I’ve read people online saying you could short it as well, but if another high load passes through you would probably do permanent damage.

Aligning the fuses is incredibly frustrating.

Flux would make it easier because it wouldn’t be pushed around by my breath or accidental pushes with my tweezers (nervousness and caffeine shouldn’t mix!).

I also had to cut very very thin pieces of solder with a hobby knife.

It was annoying to cut pieces with guesswork only to see that even though you cut it in half 3 times it’s still bigger than the fuse.

It took me ages to properly align and apply the first solder — It took me ages to properly align *and* apply the first solder

(dry tacking was impossible). Plus you can’t touch the actual fuse with the soldering iron or it’s busted. I was getting anxious because my 10 Hours Classical Music for Concentration video was reaching the end.