4KSM90PS7ER0 KitchenAid Mixer - Instructions

Dismantled the mixer, took photos, and re-assembled unit.

Removed the rear cover to inspect the speed board. Replaced motor brushes and noticed the motor body nuts were loose and 1 was completely off. Cleaned up speed board and replaced the motor body nuts, tightened with nutdriver, adjusted speedboard governor screws and with new motor brushes worked like a charm. The very rough sounding motor noise was gone and the mixer has not operated so quietly ever.

You tube has great instructions! I would suggest when you buy a part to let customer know that they need a food grade gear grease ordered to complete the reinstall of all gears and body parts!

I replaced the phase control board because the mixer had only
one speed and was surging. I noticed from other posts that it
is important to note the setting of the speed plate before you
remove it in order to remove the phase control board. Also be
careful removing the associated 'slip-on' terminals as it would
be easy to damage the speed plate. If I ever do this again I
will go ahead and replace the speed plate, probably the cheapest
item to replace. The operation was a success and the mixer is
back in business. Thanks.

I watched a YouTube video all the way through, then watched each segment and followed along with the video. It was messier than the professional repair guy, but it worked out fine. This is not a difficult repair when you can watch a video and follow along. It saved me about $130.

INSTALLED PHASE CONTROL BOARD AND SPEED CONTROL PLATE, BOTH AT SAME TIME
Your DYI video was helpful, especially holding the spring with a cloth. Also good for fine tuning to get the speed exact

watched how to repair

Took each area apart. Replaced the gear and reassembled it.

Went to partselect, found model number, printed blow-up of mixer. Figured out disassenbly procedure. Drove out main pin removing mixer head from stand. Save pin. Drove out pin in mixer main shaft which allowed planetary head to be removed. Save pin.
Removed stainless steel bezel to expose screws for removal of bottom half of mixer body. Removed screws and carefully separated mixer halves using two screwdrivers as prybars. Care must be exercised to prevent chipping of paint on body.
Separated body. cleaned grease from gears to find actual problem. Removed broken geartooth and grease near broken part to make sure no small broken chips remained. Removed pinion shaft assembly, drove pin from gear releasing broken pinion/shaft. Save pin/
Cleaned grease from pinion shaft assembly using mineral spirits and a small brush to reveal how part could be disassembled. Ordered part immediately on-line. Part arrived 1 business day after it was ordered.
Reversed process for replacing pinion shaft. Applied fresh grease obtained from excess already in mixer, spun pinion shaft to make sure grease was properly distributed. Reinstalled pinion shaft assembly. CAREFULLY plugged in mixer and jogged motor to make sure all was free and that mixer worked. If you can repair this mixer, you should have enough sense to do this diagonistic. Keep fingers away from all moving parts, don't touch expposed electric wires. Plug in only after making sure switch is in off position. Jog using mixer switch. Make sure mechanism is free.
Complete re-assembly by following blow-up and reversing disassembly steps. It may be good to write down you disassemblly procedure if it is possible that you won't be reassembling within a day or two.

Replaced gasket and O-ring. Problem solved. POC (Piece of Cake).

Unscrewed the existing screw cap, put the new one in place, replaced the screws. So easy!

Followed web site's videos. One step left out of video.

With a screw driver remove the screws holding the old base in place. With a flat head screw driver carefully pry and remove old mixer base. With 600 grit sandpaper clean and make smooth any burrs or rough spots in the mixer base recessed area. You can use some light grease and coat the outer edges of new mixer base and place in the now cleaned mixer base recessed area. The new base maybe a tight fit and not be fully seated in the recess. If a tight fit, place the piece of 2x4 piece of wood over the new part that is in the recess and carefully tap the base home using the sledge hammer. Check to see, if the base is fully seated. If not fully seated, tap again When fully seated replace the screws. You may have to adjust the height of the stand mixer head with mixer paddle attached for proper clearance between bowl and paddle. See your mixer manual for adjustment procedure

I watched the university of YouTube videos, and followed their instructions.

replaced gear, and brushes.