Control board replacement

First check the simple things, are the brushes in properly, they are keyed to only fit properly one way. Look in the hole with a torch and line the missing corner up with the blocker right inside. If you have fried something it could be damaged switch contacts on the black control plate or even weaker would be the phase board at the top just under the back cover. Testing for circuits with a multi meter will prove everything except the phase board. If you have circuits everywhere they should be then change that board.

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You really need to get a Multi meter and follow the power, you have replaced the phase board so we can probably discount it being that.
First check that the switch contacts behind the black control board are really touching when you move the speed control lever to turn the mixer on.
Next the cable, do you have continuity from the wall plug to the control board on phase & neutral, (Check green earth wire as well for the sake of safety) that will be the black wire and the white wire on the 2 lower plug in contacts on the black control board at the back.
Next remove the carbon brushes, do they have reasonable length and most importantly are they fitted correctly with the corner key aligned with the blocker at the bottom of the brush holder.
Next with brushes out check for field winding continuity. On the other side of that black control board to where the power comes in there will be a red wire and a white wire that disappear into the motor housing. One of the wires will have a circuit to one of the brass brush holders and the other wire will have a circuit to the other brush holder. The resistance of both of those circuits should be pretty much identical.
After you have done those tests you should begin to have a clue as to where the problem lies.

the K45 was introduced in 1962 and ran until 1978 when the K45SS was introduced. You have an open circuit inside, you need to open the machine from the rear and look to the power cord connections. make sure that the wires are connected and none are floating loose. the next step would be to replace the speed control switch. then check your carbon brushes if either one of the brushes are down to the nubs then it would cause a short when you turned it on, if that is the case then be glad that you have breakers and not fuses because you would have fried your motor. the speed control switch has no power attached to it. ifg the problem still exist after checking power cord, speed control plate and brushes then you have a fried armature or stator either can short the system if they have a burned wire inside especially the stator.
let us know how you fare on this after you check out the first easy steps, we can help with the harder fix also.

it was stuck on high speed because the phase control board went out, your fix may not be absolutely 100% and it is now causing an uneven distribution of the electric charge in the mixer and it is arching. My recommendation is to replace the speed control board (black and copper plate) and the phase control board. i bet it fixes the problem as these are the two parts that regulate the electricity in the mixer. Hope that helps. Buy the way if you don't fix the problem and continue to use the mixer you may have to replace the motor eventually as you can cause the armature and stator to short or burn out.

Maybe Maybe not. There is a computer style speed control board inside the mixer that can get real hot when the mixer is over loaded and the circuit can burn out, $30.-$35.00 dollar part easy fix, or the motor at $90.00 to $100.00 to replace. You can do either fix yourself with the new design. I have only replaced one motor in the Kitchen Aid mixers in all the years I have been fixing them. Only replaced one full motor. Go to kitchenaid,com and download a parts list for your model from the support tab and it will guide you to the part number and the path to follow to fix it. of course if it is under warranty KA will fix. If you are near an authorized repair center you could take it to them the part and labor to fix $165.00 if motor, $80.00 if they have to replace the board. If you are adveterous you can DIY.

It has been my experience with knocking kitchenaid is one of three reasons all related to the speed control of the mixer1 speed control board adjust speed screws2 speed Phase control board, needs replacing3 The motor governor behind the speed control board needs replacing
Speed board = $9.00Phase Board = $20.00Governor = $10.00Your time + one week for ordered parts asnd one hour to remove and replace.

all work is performed at the rear of the mixer and you need only a phillips #2 screwdriver, a pair of needle nose pliers, an 11/32 open end wrench (you will need this to adjust your speed control board after new install) and that's it. easy work all remove and replace. Oh! make sure that you pit some thermal paste behind the phase control board to avoid burn out.


But!!! before you buy parts and do all that, try adjusting the speed contol board first. Go here for a parts list for your model.


http://shared.whirlpoolcorp.com/product_literature/search_results.jsp?searchTerm=KV25G0X&siteCd=KAD&userType=Servicer


then go here for instructions on tuning the mixer speed.
http://www.youtube.com/watch?v=pUo_ZU5xh3o

if after you tune it you still get the knocking then use the parts list to order parts. two good parts sources are goodmans.com and mendingshed,com, they are reliable and have the parts in stock.

i believe if the board is black, it has burned out. Check the part no. of the control board. It could be 9707220 or some other no. Search for the spare part online. once you get it replace the board and you're good to go! BTW, the board is "plug and play" doesn't need any soldering etc. Just plug in the wires and it'll work.

http://shared.whirlpoolcorp.com/assets/pdfs/literature/Repair%20Part%20List%20-%208211761.pdf

has the breakdown of the parts. Item 8 is the controller board and item 9 is a sensor which monitors the speed. If either one is fried it will run wide open and then quit.

If you look into the brush holder you will see a stopper at the botom ,(this is so when brushes are wore the spring is not driven into armature) .. the brushes have to be inserted so the groove is lined up , try that