Nordictrack T5.7 speed fluctuations

I have the model number ntl61011.4 nordictrack treadmill. I recently replaced the motor which died after ten years, and since then, my wife swears it speeds up on her by half a mile per hour or so. Since I've had the whole darn thing nearly apart, and fiddled for days to get the belt tension set properly, I have some time and spare parts invested in this thing and I'd like to see it limp on. I've seen the treadmill doctor video on speed fluctuations, and I'd like to rule out mechanical issues. The belt moves freely with the treadmill off, the motor runs smoothly, the belt and walking board are indecent shape, though I do have a new replacement belt to put on if I need it. I have just lubed it recently. The odd thing is, after much research, I tried the calibration for it, and it's not sensing any speed while the belt is moving. I've looked at the parts list for this model, and it appears to be the first model in the T5.7 series that does not have a reed switch, and I can assure you there isn't one there. I've looked for other ways the treadmill can monitor speed, and aside from an optical sensor, I'm a bit clueless at this point. ICON fitness said that it was the reed switch when I called, and after I told them mine did not have one, twice, they said it was the MCB which I find hard to believe. The machine passes it's own self test in the information mode. The LED on the board is solid when powered on, and blinks steadily when the walking belt is moving. I don't have the best DMM, but I measure 3.5 volts on the green tach wire, which should be fluctuating between 0 and 5 volts, so I'm inclined to think that's ok, as a meter not designed to read that like an O-scope would show an average. I even confirmed this reading at the connector going into the console to insure no wires were pinched up there. I was wondering if the speed increase could be caused by a surge in the outlet power, as my wife says it rarely happens in the morning when most things in the house are turned off. Also, how the heck does this thing monitor it's own speed?

Also, many thanks for taking the time to help the DIYer's out there like myself, this is your business and it's great to see help even without a bill. Especially when parts are so expensive already.


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