Question about Precor Exercise & Fitness
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The speed sensor is a hall effect sensor that emits a pulse when a flywheel lobe passes between
its transmitter and receiver. The speed control circuit processes the pulse train emitted by the
speed sensor. The speed sensor signal is a real time representation of the operating speed of
the treadmill. The speed control circuit compares the real time speed (speed sensor output) with
the speed that it expects the treadmill to be operating at and acts accordingly to control treadmill
speed or initiate an error code sequence, if necessary. Typically, if a problem exists with the
speed sensor the drive motor will operate (perhaps only briefly) before a speed related error
occurs (errors 20-26).
1. Set the treadmill circuit breaker in the “on” position. Using a DC voltmeter, measure
the voltage between terminal 3 of J2 (green wire) and terminal 4 of J2 (black wire) on
the lower PCA. Slowly, rotate the drive motor flywheel. The voltage should read
approximately 5 Vdc when a flywheel lobe is between the speed sensor “legs” and
approximately 0.25 Vdc when a flywheel lobe is not between the speed sensor “legs”
2. If the voltages in step 1 are correct, go to step 5. If the voltage in step 1 is 0 Vdc or
significantly low when a flywheel lobe is between the speed sensor “legs, continue with step
3. Measure the voltage between terminal 1 of J2 (red wire) and terminal 4 of J2 (black wire) on
the lower PCA. The voltage should read approximately 5 Vdc.
Sensor C954, C956 Treadmill
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4. If the voltage is missing or significantly low, disconnect the speed sensor plug from the lower
PCA. Measure the voltage between pins 1 & 4 of the J2 plug on the lower PCA. If the
voltage is approximately 5 Vdc, replace the speed sensor. If the voltage is missing or
significantly low, replace the lower PCA.
5. At this point the speed sensor output is good, but a speed error occurs. There are two
potential causes for this condition. They are upper PCA or lower PCA. There are no good
means of troubleshooting these components other than substituting known good
components. Replace only one component at a time. If the component that you replaced
does not correct the problem, replace the original component. Try substituting the lower
PCA first then the upper PCA, if necessary.
tips extracted from the technical manual Precor956
Posted on Sep 14, 2010
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