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My Pro-Form 755 CS treadmill speeds up and slows down on its own.

My Pro-Form 755 CS (model # 831.299570) does not maintain the speed I set it to. It speeds up and slows down while in use but does not get to the speed to which I have set it. I followed the diagnosis instructions for the Power board and the motor contoller board and they both checked out OK (according to the LED lights). The belt does seem to be adequately lubricted. I noticed that the choke has been humming loudly lately and now when I tap on it while the motor is running, the humming changes and sometimes disappears. However, the speed problem continues. Does this sound like I need to replace the choke? Is there a way to definitively diagnose this before I order the part? I believe the part number of the choke is 130993.

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Treadmills , Home Cardio
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Manage My Life
Ken, the belts on Proform and Sears treadmills are lubricated for life at the factory. Over the years we have had issues with walking belts losing the lubrication and Proform found we could use a special lubricant to extend the life of the walking belt. Your next step would be to test the amp draw of the motor as you jog on the treadmill and with no load to see if the motor controller is increasing voltage to the motor as the amperage increases. The most common problem in these issues is a failed motor controller.
by Manage My Life
January 9th, 2012
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I followed the calibration steps you provided and everything checked out OK; however, the problem still persists. I don't believe belt lubrication is the issue as my owner's manual states that the belt does not need to be lubricated and that doing so may lead to belt deterioration. What should my next step be?
by Manage My Life
January 8th, 2012
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Ken, I am sorry the problem returned. I recommend you start at the top of this thread and go through the tests that were recommended. You might find the lubrication in the belt has worn out or one of the boards needs calibration.
by Manage My Life
January 6th, 2012
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I'm sorry to report that my problem with maintaining speed has returned. I installed the new choke a month ago and everything was working fine until recently. Now, I'm starting to experinece the same problem I origianlly had. When walking on the treadmill, the speed is maintained properly. However, when I speed things up and jog on the treadmill, the motor has again started to vary speed - it will slow down, then try to speed up to reach the speed I have set, but struggles to maintain the proper speed. This is exactly how the original problem presented itself and I anticipate that it will get worse as time goes on. What should my next step be?
by Manage My Life
January 6th, 2012
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Manage My Life
I am glad you found the problem. Thanks for using Manage My Life.
by Manage My Life
November 29th, 2011
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Your suggestion worked. When I bypassed the choke coil the motor ran fine and kept a constant speed. I'll order the new coil. Thank you for your help.
by Manage My Life
November 29th, 2011
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You can jumper between the 2 wires that go to the choke. You will need a jumper to go from the connection on the circuit board to the motor. Remove the choke wires. I don't recommend running the motor long term without the choke. The motor should run smoother with the choke. Be sure to disconnect the power to the treadmill before changing the wires from the choke.
by Manage My Life
November 28th, 2011
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One more question: can I run the motor without the choke coil long term or would that shorten the life of the motor?
by Manage My Life
November 28th, 2011
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How should I bypass the coil and connect the motor directly? Can I just jumper between the two connectors? I believe one wire from the coil goes to the motor and the second wire from the coil goes to one of the circuit boards.
by Manage My Life
November 28th, 2011
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Manage My Life
The easiest way to test the choke is to remove it and connect the motor without the choke. The choke is a coil that is there to make the motor run more quietly. The motor will work fine without the choke.

I am sending an image showing how to calibrate the console with the motor controller. Sometimes this calibration will be off and cause the speed to slow and speed up.

To test the walking belt lubrication, do not turn the treadmill motor on. Set the elevation to the highest level. Stand near the front of the walking belt. Push yourself firmly toward the rear of the treadmill. If the belt is properly lubricated the belt will take you to the rear edge of the treadmill and dump you off on the floor. If you move and stop, the belt needs lubricating.

The part number for the belt lubrication kit is 219168. You can buy it at [searspartsdirect.com]. The cost is around $4.00. The application instructions should be in the package, but in case they are not here is how to apply the lubrication.

Turn the walking belt until the belt seam is along the top of the front roller. Raise the belt on one side in the center of the walking board front to back as high as you can. Apply ½ the tube of lubrication to the walking board in a zig zag fashion moving from front to back. Move the belt until the seam comes up on top of the rear roller and lift the belt again and put the rest of the lubrication on the walking board in the same manner. Turn the treadmill on and walk on the belt for 10-20 minutes. Walk all over the belt to distribute the lubrication evenly on the walking belt and board.

To test the walking belt and board for wear, lift the walking belt and inspect the top of the walking board and the bottom of the walking belt for worn spots. Both surfaces should be smooth and slick. If you find worn places on either part, it should be replaced.
by Manage My Life
November 28th, 2011
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A treadmill is definitely something we depend on and when it begins to malfunction it can be a huge inconvenience. While you are waiting for an expert to respond, I have attached some helpful links below that may provide information to assist you with your question.
by Manage My Life
November 25th, 2011
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