My TX400 would run for 7 seconds, and then stop. I removed the front cover, and discovered that the large plastic pulley had slipped on the front roller, and moved inward away from the speed sensor. There is a little small magnet on the pulley that triggers the speed sensor, and in my case the pulley had moved inward bringing the magnet away from the sensor. To remedy the problem, I first removed the two allen head bolts holding the front roller to the frame. The plastic pulley was easily removed from the roller. I then roughed up the inside of the pulley with 80 grit sandpaper. Don't go too far, just rough it up. Clean the roughed up area with an alcohol swab and wipe dry. I mixed up a little two part epoxy, J-B Weld, and applied a light coat to the inside of the pulley. Install the plastic pulley, with the small round magnet facing out, on the opposite end of the roller. The surface there is rougher and not worn smooth. Position the edge of the pulley approximately 1/16" in from the edge of the roller, and wipe off the extra epoxy. After allowing the epoxy to set overnight, i installed the roller and tensioned the belts. No problems since.
Twicebit, October 2011
