Precor C842 Service Manual page 29

4. Connect a DC voltmeter across resistor R25, See Diagram 6.5, and pedal the bike for a
minute. Stop pedaling the bike. Slowly rotate the secondary pulley by hand until the magnet
mounted on the flywheel passes the speed sensor. The DC voltmeter will read 0 Vdc when
the magnet is away from the speed sensor and 5 Vdc when the magnet is near the speed
sensor. If both voltage readings are correct, skip to step 6.
5. If either voltage reading in step 3 was incorrect, set the on/off switch in the off position.
Connect an ohmmeter across capacitor C24, See Diagram 6.4, and pedal the bike for a
minute. Stop pedaling the bike. Slowly rotate the secondary pulley by hand until the magnet
mounted on the flywheel passes the speed sensor. The ohmmeter will read open (∞) when
the magnet is away from the speed sensor and approximately 100 Ω when the magnet is
near the speed sensor. If both ohmmeter readings are correct, skip to step 7.
6. If either ohmmeter readings is incorrect, perform the same ohmmeter readings using a
strong external magnet instead of the magnet on the secondary pulley. If the ohmmeter
readings are still incorrect, replace the speed sensor. If the ohmmeter readings are correct
using an external magnet, adjust the gap between the magnet, mounted on the secondary
pulley, and the speed sensor to approximately 1/8 inch. Repeat the ohmmeter
measurements in step 5. If either ohmmeter reading is incorrect, replace the secondary
pulley (with magnet). Skip to step 10.
7. While pedaling the cycle, measure the voltage across the C16 capacitor with a DC voltmeter
(See Diagram 6.5). The measurement should be approximately 8.9 Vdc ± 0.5 Vdc.
8. If the voltage is missing or significantly low, disconnect the lower interconnect cable from
connector J4 on the lower PCA. Repeat the measurement in step 7. If the voltage is still
missing or significantly low, replace the lower PCA.
9. If after disconnecting the lower interconnect cable in step 8, the voltage across the C16
capacitor was correct, check the upper, lower interconnect cables and junction block per
Procedure 6.1.
10. If one of the interconnect cables or junction block is not the problem, replace the upper PCA.
11. If you have performed all of the previous tests and have not been able to locate the trouble,
call Precor customer support.
12. The C842. C846i and C846 version 2 do not use a speed sensor like the C846 version 1
units. Instead the system monitors one of the three phase generator windings. The system
monitors AC zero cross. The monitoring system notes every time the generator AC voltage
passes through zero volts. By counting the zero cross rate, the system knows how fast the
generator is turning. The system calculates the user RPM from the generator speed. If the
system does not see a zero cross rate, it assumes the bike is not being used and the display
will not illuminate when the bike is pedaled.
13. Disconnect the generator leads from terminals M3 (red) and M4 (black) on the lower PCA.
Connect and AC voltmeter to the leads removed from terminals M3 and M4. Pedal the bike
at about 60 RPM (1 rotation per second), the voltmeter should read approximately 120 Vac.
If the voltage reading is absent or extremely low, replace the generator.
C842, C842i, C846, C846i Upright and Recumbent Cycle
Page 29