This error monitors the treadmills power bit reading when the treadmill was operating at speeds
above 1 mile per hour. Power bits indicate the relative time that the motor controller drive circuit
is turned on. Therefore power bits is an indication of the amount of power the load is demanding
from the motor controller. Error 21 indicates that at a speed of greater than 1 mile per hour an
excessive amount of power is being demanded from the motor controller.
1. The running bed and/or running belt is badly worn and the error 21 occurs while the treadmill
is being used..
2. The drive motor brushes are badly worn and not making sufficient contact with the drive
motor commutator. The error 21 occurs while the treadmill is being used. The treadmill may
also bog down when the load or speed is increased.
3. Some lower PCAs require a jumper when installed in 120 V.A.C. treadmills.
4. On treadmills utilizing an SCR motor controller, a leaky or shorted drive motor filter capacitor
could raise the current demand sufficiently to cause the error 21.
5. On treadmills utilizing an SCR motor controller, a leaky or shorted drive motor inductor could
raise the current demand sufficiently to cause the error 21.
6. A shorted or de-magnetized drive motor is causing the high power demand.
1. A clamp-on A.C. ammeter must be used to determine the amount of A.C input current being
drawn by the treadmill under no load and loaded conditions. The current readings can be
used to determine the condition of the running belt and/or running bed. These same readings
should be taken on a similar unit with a known good running belt and running bed. Those
readings can then be used as a benchmark for future use. Replace the running belt and/or
running bed as required. Remember, many running beds are double sided and the bed can
be flipped over rather than being replaced.
2. Replace both drive motor brushes.
3. If the lower PCA requires the 120 VAC jumper and the jumper is not installed, the treadmill
will typically display an error 21 between 7 and 8 M.P.H. Install the lower PCA jumper to
correct this problem. WARNING: Be sure the treadmill is a 120 V.A.C. unit before installing
the jumper. Installing the jumper on a 240 V.A.C. will cause the lower PCA to fail.
4. A clamp-on ammeter should be used to measure the A.C. input current at no load. The filter
capacitor should then be electrically isolated from the drive motor circuit. The drive motor
leads must be kept intact so that the drive motor will operate with the filter capacitor removed
from the circuit. The no load A.C. input current should be measured again, if the A.C. input
current is significantly lower, replace the filter capacitor.
5. Use the same procedure as in step 4 above, except remove and isolate the inductor from the
drive motor circuit instead of the filter capacitor.6. A known good drive motor must be substituted for the existing drive motor.