Yes, we also had the situation of our TX 5.0 RC suddenly developing the problem of operating only for a few seconds, then shutting down with the the numeral "3" appearing on the pulse display. As others have indicated, it is due to a broken plastic disc on the forward tread roller which when operational and in conjunction with the adjacent "electric eye", senses the speed of the unit.
As a Mechanical Engineer, here is what I found-- and the cure thereof. Since the control circuitry of the treadmill does require the pulsed input from the speed sensor (i.e., disabling of the sensor by pulling the internal plug does not work), and since a replacement plastic disc doesn't seem to be available from any source, the only option is a repair:
1. Unplug your line cord from the wall socket.
2. Remove the lower front cover ahead of the walk area (four Phillips head screws).
3. You should immediately spot the broken (or perhaps just cracked-through) black plastic disc on the right-hand end of the forward tread roller.
4. Although some people have had some (limited?) success in mending the disc while in place on the roller, I chose to do it after removal:
a. Relax tension of the walking belt via counter-clockwise rotation of the adjustment bolts at the back end of the unit. Although the manual refers to two such bolts, mine has four. You'll need a 5.0 mm Allen wrench (may have been supplied with the unit). Do an equal loosening of all bolts, and count the number of turns (I used four complete rotations) to simplify the later re-tightening of the belt.
b. Remove fastening bolt at right-hand end of forward roller (6.0 mm Allen wrench)
c. For later installation of repaired black plastic disc, the bolt at left-hand end of the forward roller may also have to be loosened, but not removed.
5. As can be observed, the plastic disc is somewhat complex, with both an inner hub and an outer hub, along with the outer disc which has the rectangular holes providing the speed pulses. The only original attachment between the inner hub and the forward roller is a "press fit" between the two. This is the source of the problem, since the plastic eventually fails because of the resultant stress.
6. Using a sharp knife, remove the plastic residue at the inner hub, which is present due to the initial press fit.
7. Glue the plastic disc back together:
a. Although there are glues which provide a better bond for plastic, super-glue may be the best choice here, since it is quite liquid and can therefore fill all cracks. An examination of the inner hub will probably reveal the start of additional cracks, which can/will lead to an additional failure within a few months if not addressed.
b. Apply glue to all broken surfaces and additional cracks.
c. Fit broken portions together and apply pressure with rubber bands around outer hub.
d. Allow to "dry" overnight.
6. Remove rubber bands (since they are too thick for the clearance between plastic disc and "electric eye").
7. Apply tape to peripheries of outer hubs. I recommend two wraps of Scotch brand reinforced shipping tape. Wrap in the direction such that outer end of tapes will not rotate into the electric eye.
8. Gently tap repaired disc into correct position on right-hand end of forward roller. If disc should again fracture, repeat from step 7 above. If disc is loose on roller, apply glue.
9. Re-install bolt at right-hand end of forward roller (and re-tighten the one on other end if needed).
10. Re-tighten walking belt tension using adjustment bolts at back end of unit. (Note: This is a good opportunity for lubrication.) If returning these bolts to original position results in a skewed belt, adjust per Sportcraft's instructions.
11. Re-install lower front cover, plug in the line cord, and enjoy!
Dean, the engineer
August 2014
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