I have a pretty small yard with little grass, so didn't need much of a string trimmer. End up purchasing the Homelite UT41112B 13" String Trimmer. It was humming along serving its purpose just fine. Nothing fancy but gets the job done. Probably about 2 years after I bought it I was out whacking weeds away on our parkway and it just stopped.
Now I realize this trimmer retails at HomeDepot for $30, which is pretty close to a throw out and replace price, but that is a lot of working hardware to fill up and a landfill with. Especially if the replacement only lasts a few years too. So I took to the task of repairing it. Its a simple machine so I knew it couldn't be too hard.
When examining it, I noticed that all the air vents were clogged with dead grass clippings preventing airflow. After taking it apart and checking components I figured out that it has a thermal fuse (AUPO BF157) which had blown from the lack of airflow from the clogged vents. After looking around in the unit there is not much else to even break. So if your unit just stops working, it is very likely this fuse. I ordered the fuse from Ebay and waited for it to arrive. Make sure you order a few, they usually come in a 5pack. You may blow some out getting it in.
Items needs for Homelite UT41112B 13" String Trimmer repair:
Phillips screw driver
Soldering iron and solder
AUPO BF157 Thermal fuse (Usually costs around $5 for 5 + shipping)
Heat shrink tubing.
Some way to heat the heat shrink. (I bought an expensive hot air gun from Amazon that has some in handy for other projects as well, but you can do it with a hair dryer or lighter)
The housing comes off by removing the screws and pulling it apart. Once opened you'll see the electric motor with the fuse surrounded by heat shrink and tucked up by the windings.
Remove the zip ties and cut off the wrapping to expose the AUPO BF157 thermal fuse.
Once that is completed you can desolder the joints and remove the fuse or cut it it out. I ended up cutting it. Then solder in the new fuse. Being careful not to overheat the fuse and blowing it out before its even installed. You'll want to make sure to put new heat shrink onto the wire before you solder it back together. Made that mistake myself. It can be a little tricky to get them soldered back together. I ended up sanding the end of the winding and wrapping it around the lead on the fuse.
Once its solder back in, slide the heat shrink tube over the wire and fuse. The tricky part for me was heating the heat shrink without blowing the fuse. I ended up covering the fuse with foil as I used the heat gun on the heat shrink. This was, of course, after I blew the fuse without using the foil and had to solder in a replacement.
I ended using a couple sections of heat shrink, each time covering where the fuse is with foil to prevent as much direct heat transfer into the thermal fuse. And Success! It runs again!
Pack the motor back into the case, and don't forget to clean out the air vents while you have it apart. After this, you should have a working string trimmer again