Blades wont spin - Cuisinart SPB-6 Smartpower 6 Speed Blender

Either the coupling from the motor with the fingers on it is not really attached to the motor shaft or the drive on the blade that engages with it is not attached to the blade shaft. One other thing is that on some models if the rubber jar seal between the beaker and the blade carrier is in the wrong place it can raise the blade drive to not engaging properly with the motor coupling. The gasket goes between the jar and the blade carrier, not under the blade carrier.

I don't have one, but inspect the shaft, it looks like there is a key on the shaft, then inspect the inside of the blade where it goes on top of the shaft, see if it looks like the shaft has spun out the blade and this is why it's not spinning.

Remove the blade and the container, then turn on and see if the shaft is spinning, it should be most are a direct drive.

So now if the shaft is spinning, that most likely means that the blade hole is broke where it sets on top of the shaft.

Look closely at the inside of the blade, you should see some type of damage like the groves are worn, I hate to see you buy one and it was the shaft that wore, but usually the blade will go first.

make sure blade is pressed tightly onto shaft... should click into indent. if not then you need a new blade piece.- stripped

This is not really the solution it is just a better description of the problem that I am also having. This is a great blender however the part where the cup blades conect to the motor is made of plastic.
So what has happened here is that the motor is fine, the cup is fine only the plastic part that makes the motor turn the blades has worn down therefore rendering the blender useless. I would like to know where I could get this small part to change on my blender!!!

The shaft has probably siezed at the bottom near the blade. The seal can fail and let liquid inside the shaft and gunge it up.
Take the orange handle apart, then unscrew the four steel pins, then pull out the motor. From the blade end, take the screw from the blade and prize it off. Then pull the shaft out from the top and clean it. It may be stuck - push a blunt nail or similar in the bottom to free it. Clean the shaft and solidified debris inside the tube. Then reassemble carefully.

Sounds like the teeth are stripped underneath the blade. Make sure it's put together correctly before you do anything else.
Download Cuisinart CBT 500 Manual

Check the blade with it off the base and make sure that it spins freely. Check the spindle on the base and see if it feels hard to turn. If the spindle turns too easy , then the connection inside the base is broken and needs replacing.

Depending on the age of your blender, a new blade assembly may be available. I would recommend calling Kitchenaid Customer Service for pricing. Their toll-free telephone number is:

1.800.541.6390

Check and make sure that the shaft in the base housing spins. If it does, the blade assembly has become disconnected from it's shaft probably due to an improper spot weld or peening of the blades to the shaft, or has torn loose or ripped the splines out due to an immovable object trying to be spun. A jammed ice cube can do this. Blade assemblies can be had usually directly through the manufacturer and usually on line. If this has helped, please rate it accordingly.

My Vitamix 3600 plus has same problem. Result of detachment of rubber coupling between lower splined socket from blade shaft. This is a tough rubber molding that takes tremendous punishment through years of smoothies. Mine showed some rust on the bottom of the blade shaft, where it parted. I tried gluing back together with super glue and tried to eyeball it. Of course it was off by a few degrees. When I reassembled and turned it on, what a racket of vibration! But it held. Amazing. Obviously not good to go though. So I took assembly all apart and redid it, chucking the shaft and the lower nut in the lathe. This time, all true on axis. Glue held for about a week. Right now I am regluing, this time with epoxy. We'll see how it holds up. And meanwhilst, I'm researching replacement parts! I'm not too optimistic about the epoxy.