Saw blade creeps down when the motor is turned on

If you can hear the motor engaging but the blade is not turning, there could be several possible reasons for this issue. Here are a few things you can try to troubleshoot the problem: Check the power supply: Make sure the saw is properly plugged in and the outlet is functioning. You can also try plugging the saw into a different outlet to see if that makes a difference. Check the blade: Make sure the blade is properly seated and tightened on the arbor. If the blade is loose, it may not spin properly. Check the belt: If your miter saw is belt-driven, check the belt to make sure it is not loose or broken. Check the motor: If the motor is running but the blade is not turning, it could be a problem with the motor. Check to make sure the motor is properly connected to the blade and that the motor is running smoothly. Check the electrical brake: If your miter saw has an electric brake, it may be malfunctioning. You can check this by unplugging the saw and removing the blade. Then, turn the saw on and see if the brake engages. If it doesn't, the brake may need to be replaced. If none of these troubleshooting steps solve the problem, it may be best to take your saw to a professional for repair.

Is the belt still on? Does the motor's weight hang smoothly down on the belt to keep tension?

MAKE SURE THE BLADE IS RUNNING TRUE, UNPLUG SAW ! BRING THE BLADE DOWN TO THE CUTTING DECK, WITH YOUR HAND TURN THE BLADE, AND WATCH WHAT THE BLADE DOES. THERE SHOULD BE NO SID TO SIDE OR UP AND DOWN MOVEMENT IN THE BLADE ! THERE IS LITTLE WASHER KITS THAT MAKE CENTER THE BLADE TO THE DRIVE. OR IF THE BLADE WIGGLES WHEN ALL IS CENTERED, IT MAY BE A BAD BEARING IN THE BLADE HEAD.... IF I WAS OF HELP HIT THE YES BUTTON.. THANKS JAY.. THE MOTOR REPAIR GUY IN LONGWOOD FLORIDA

Two easy possibilities are that the blade is dull or that the wire is too small. The wire is likely to be a problem if you are using an extension cord. You could move the saw near to an outlet that you know to be wired with 12 gage wire (not 14). Or you could buy as short as possible 12 gage extension cord. If being underwired is the problem, you will notice that the motor comes up to speed much faster when wired adequately. You might also buy a cheap new blade to rule out the dull blade problem. If neither of these fixes the problem, then the motor has become "weak" because it has overheated just enough to cause some minor shorts between the windings. (If the shorts are major it won't turn at all and will trip a breaker.) In this case the motor can be rewound, but it will probably be cheaper and easier to just replace the motor.
Good luck, Al K

motor is binding up. wait a day and see if it does it again
if so replace the motor

Exploded diagram for your SM100M miter saw is here.
User manual is here.

Page 20 covers blade change operation.

Make sure you unplug your saw! You need to remove a screw from the cover and rotate the cover to the rear. Use a hex wrench in the motor shaft to keep the saw blade from turning, and loosen the arbor nut with a 1/2" wrench. The arbor is reverse threaded, so you'll turn it clockwise to loosen, then counterclockwise to tighten it up after you have swapped the blade.
Rotate the cover back after that's done, and replace the screw.

If this was useful, please vote. Thanks.

1. Unplug the saw.
2. Locate the blade lock button used to lock the motor shaft when changing a blade. For your saw, this button is usually located on the left side of the blade guard somewhere around the motor housing.
3. Push the button while rotating the blade until the button engages and the blade will no longer turn.
4. Use the wrench that came with the saw (or another wrench) to loosen and remove the blade bolt. For your saw the bolt should have standard right hand threads which means you loosen the bolt by turning it counter clock-wise.
5. Remove the old blade and replace it with a new blade of the same mounting type. Some blades have a round through hole and some blades have a diamond through hole.
6. Re-install the blade bolt and tighten clock-wise while holding the blade lock button down.

1. Unplug the saw.
2. Locate the blade lock button used to lock the motor shaft when changing a blade. For your saw, this button is usually located on the right side of the blade guard somewhere around the motor housing.
3. Push the button while rotating the blade until the button engages and the blade will no longer turn.
4. Use the wrench that came with the saw (or another wrench) to loosen and remove the blade bolt. For a worm drive saw with the blade to the left of the motor, the bolt should have left hand threads (non-standard) which means you loosen the bolt by turning it clock-wise.

No. Unplug saw remove saw blade grasp shaft that saw blade was on wiggle back and forth. Should not be too much play. After 10 years motor bearings are proably worn. Easy to replace

Disconnect the electric from the saw. Remove the throat blade cover. Bring the blade all the way up. Look for wood  caught between the blade and anything else. Finding none,remove blade. Try motor w/o blade. If it runs now,w/o the blade then the motor is likely ok . Reinstall blade. Now if it stil stalls, Replace motor.