Belt on my dewalt dw680 planer slips and starts smoking

No it goes to a dw733 or 734 12 1/2in
look on ereplacementparts.com

REMOVE COVER SO YOU CAN SEE THE BELT, PULL THE BELT AS YOU TURN IT AND IT SHOULD COME OFF

If its been used a lot the brushes may be bad

Here is a link to a site I am a member of, Lumberjocks.com. The link is for a discussion on how to replaced the belt on your planer!
Good Luck!
http://lumberjocks.com/topics/10176

Check to see if the pulley has a screw in the end holding on the outer flange of the pulley. Some models have to remove this and slide the new belt on then refit the flange.

Use dish washing liquid to lubricate the roller and belt on both rollers and place the belt equally on each roller and move in on both rollers evenly

You can go to Dewalt's website at http://servicenet.dewalt.com/ or an aftermarket site like www.ereplacementparts.com to find good breakdown pictures of your tool. You can also order parts from them or get part numbers to search the web for better prices.

The pully which quides the belt must be perfectly level in both the horizontal and vertical positions. Use a metal square to check alignement and adjust using adjustment screws.

Couple of things to check:
1. Are your knives sharp? Dull knives will cut not fast enough to keep up with the rollers.
2. What is the depth of cut? Dewalt's planers cannot plane a board to excessive depths.
3. Are you rollers clean? Dirt, pitch or possibly grease could affect your feed rate.
4. The belt/chain for your rollers engaged or are they slipping? Open up the planer and check for wear or possibly broken belt/chain.
Snipe is usally caused by improper support while exiting the planer. Use outfeed rollers set to the correct height. Also chek that you outfeed bed is aligned with the bed of the planer.
Hope that helps,

Go to Dewaltservicenet.com and in the middle of the page towards the bottom is a box indicating manuals/breakdowns. Type in your model number and you can download one this way.