Transformers convert 110 volts alternating current, or AC, to low-voltage direct current, or DC, using internal coils of wire. A transformer has no moving or serviceable parts, and if the internal wirings burn out, you will need to replace the transformer. However, transformers rarely go wrong; if they do, it usually means the fuse on the AC plug or the fuse on the transformer has blown. If you find your transformer isn’t working, then chances are replacing the fuses will repair it to working order.
Locate the fuse cover, which is usually on the base of the transformer, but it may situated in other places. If the cover is held in place using a small screw, remove the screw using a screwdriver, then lift off the cover. If it clips in place, use a small flat-head screwdriver to pry it out.
Unclip the fuse from the fuse holder using your fingers, or if it’s the type that pushes in place, use your fingers to pull out the fuse. Put a new fuse in the fuse holder by pushing it in place. Make certain it has the same rating as the old fuse.
Replace the fuse cover. Either clip it in place, or insert the screw and tighten using the screwdriver. Test your transformer to see if it’s repaired. If it’s not, then replace the fuse in the AC plug.
Remove the plug from the AC electricity supply, and then remove the fuse cover or plug cover to get to the fuse. If the plug has a fuse cover, lift off the cover using a screwdriver, then pull out the fuse. If the plug doesn't have an external fuse cover, then remove the cover off the plug using a screwdriver. Pry out the fuse from the internal fuse holder using your fingers or a screwdriver.
Put a new fuse in the fuse holder, ensuring it has the same rating as the old one. Replace the fuse cover by pushing it in place, or replace the plug cover and use the screwdriver to tighten the screw.
Insert the plug into the AC wall socket. Test the transformer. If it works, then you’ve successfully repaired it; if it doesn’t, your only option is to purchase a replacement.