My KitchenAid RRK150 325 Watts Stand Mixer started to smell more and more when used for more than 5 minutes. Now it doesn't work anymore, nothing happens when power is on. I'm not sure whether it's the motor or the speed control. Also, I couldn't open the cover to get to the motor.

Apart from checking a fuse, there is little more you can do. Did you notice a loss of power or burning smell the last time you used this? What make and model you have may help others identify a known problem with your machine.

Kind Regards, Dan.

We need more information if we are to help. Does it do this every time you turn it on or did it happen once and it will not run anymore. Is there any noise when you turn it on or does it smell or spark when you turn it on. Please more info.

smell the motor housing for any burnt smell.suggest you buy a new one.theire not worth fixing

Check the fuse, and the bowl should be in place

Is the blade in the working bowl free turning?

Obtain a copy of the KSM150PS Repair Part List from Kitchenaid.com.
Download a Copy of the Kitchenaid Service manual.

http://www.kitchenaidparts.be/centers/servicemanual/mixer.pdf

Inspect all the moving parts: Speed Lever, Speed Link, etc. and
make sure nothing is loose, bent or broken. Tighten all the screws
if necessary. Finally, adjust the mixer speeds if needed:

Remove the screw holding the End Cover and locate the three screws from the Control Plate.
All three (2 top left and right, and 1 bottom) must be adjusted.

1. Loosen the lock nuts enough & Turn the 2 top screws clockwise until they cannot be turned
anymore. Leave the bottom screw alone for now.
2. Use a dab of white paint or paper whiteout to mark the positions of the Phillips screws.
3. Plug in your mixer and Set the speed selector to "Stir".
4. Turn each top screw One full turn couterclockwise (alternating between Left and Right)
Keep making one full turn at the time (for both left and right) until the motor starts running.
5. Put your hand near the Agitator shaft and allow it to brush your finger slightly. Use your
watch or clock and start counting the number of times the shaft touches your finger in
60 seconds. The correct count should be 60 RPM (Rounds Per Minute). If it is less
or more than 60, give each screw 1/4 turn counterclockwise or clockwise and start counting
again. Now tighten both lock nuts.
6. Set the speed selector to "6" and turn the bottom screw either clockwise or counterclockwise
to achieve a speed of 180 RPM.

For your reference, the planetary RPM's for the 5-qt. tilt-head Artisan Stand Mixer are as follows:
Stir speed - 60
Speed 2 - 95
Speed 4 - 135
Speed 6 - 180
Speed 8 - 225
Speed 10 - 280

Counter top appliance number for Kitchen Aid is 1-800-541-6390 M-F 8 - 8 EDT and Sat 12 - 5 p.m. they should be able to help you

i think its time to retire it its has had a good run time to put it to rest and buy a new on it don't sound safe to use anymore

Found this,may be helpful.
Why do I see oil leaking from the beater shaft of my stand mixer?
Some KitchenAid® stand mixers that are not used very often or have been tipped may experience slight oil leakage from the shaft or hub attachment. To avoid the oil leakage, KitchenAid suggests that you run the mixer weekly for short periods of time. Generally, the mixer may lose approximately X cup of oil before repair is necessary. The oil used is FDA approved and is not harmful to consume, should any get into the food that you are preparing.
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http://www.tradebit.com/filedetail.php/3861005-kitchenaid-mixer-service-manual

Service manual for the mixer