|Electrical||Armature||The armature has bearings either side of it so check that it spins freely. Check the windings for any burnt or broken windings. The shiny metal that the windings are wrapped around can be cleaned with an eraser to remove carbon, and check that there's no broken or undercut edges. ||Changing the brushes frequently can help save the armature from carbon build up and undercutting. Also, whenever you can, blow some compressed air across the vents on the housing to clear out crud from the brush holders and to keep the armature spinning freely.
|Electrical||Field||The field is an assembly of wire wrapped around the metal holder and these wires can get burnt or fray with age, and that can stop the armature from spinning.
Also, if your tool is spinning the wrong way - there's a very good chance the Field is in backwards.
There's 2 windings on a Field so use a multi-meter and check for continuity across each side. Note the value of the first side you check (say "3" - pretty common) and check that the other side is within 10%.||Over-amping can affect the Field so try to keep the armature and motor as free of crud as you can.
Don't cover the vent holes with anything, like your hand, as this can cause the over-amping and so can the wrong gauge of cord. This often happens if you're using an extension cord of the wrong gauge. Don't skimp on extension cords it's not worth the cost of your tool repair, and don't use too long of cords for the same reason.
|Electrical||Power||This is a fairly wide thing to check, but start at one end and work to the other. If your tool has a power cord, for example, is the socket working? For a battery tool, are the contacts clean and good? Sometimes smacking the battery can help there||Please see our advice on Cords and on Batteries.
|Electrical||Switch||Using a multi-meter test the continuity across the switch from input to output, if there is no continuity - replace the switch||Cleanliness and age are the main things here. Try and keep the switch as clear of crud as you can and routinely pull it apart to make sure the connections are good and the switch is clean.
|Mechanical||Bearings||Bearings wear down and when they do tend to get noisy, or difficult to rotate so these signs might help.
It's not really worth it to replace with cheap bearings.
A repair shop can help yo out with getting the bearing pressed on or off (especially if you buy from them).
Bearings are either rubber or metal sided so if you're replacing a bearing that is exposed to crud, etc think about upgrading to a metal sided bearing.||At the risk of being repetitive ... yup, keep it clean with lightly blowing air across to clear out crud.
|Mechanical||Chuck||Doesn't hurt to keep a spare chuck screw (if applicable) as they can snap - remember that it's reverse thread.
One or more of the jaws may have slipped as well so a visual inspection will help you there.
||Replacing a chuck is fairly straight forward and a breakdown drawing can really help.
Note that you can also upgrade your chuck at this point ... just an idea.
|Mechanical||Gears||Gears go by over-use or just age and the mobility of the assembly will give you a good idea of the grief.
On drills, the gears can go from over-amping where the tool is working too hard from: pushing it, covering the vents, poor extension cords, worn brushes, etc.
For saws, gears can go because the raise/lower assembly is dirty or crudded up.||Routine maintenance sure helps here as cleanliness all-round is important.
|Mechanical||Handle||The handle assembly naturally goes through a lot of use, but there's also some designs out there that could be better.
Try to always carry using the grip recommended by the manufacturer and this isn't always the handle.||The handle usually houses the switch so when working on the handle have a look at the switch.
Sometimes further cracking or damage of the handle can be offset with epoxy as a stop-gap measure.
|Tool||Drill Hole Hawg|| ||